Sagittronics : Charlie Slick

Potentiometer as a voltage divider, when does the value of the pot make a difference?

noreply@blogger.com (Charlie) — Wed, 02 Sep 2015 00:17:00 +0000

Knowing what you can and cannot change about a circuit can make projects much easier There have been several times in the past, in which I've found a circuit I liked, but been annoyed because it had bizarre potentiometer values, and I've wondered, "can I just use whatever pots I want?"

For example, the yu synth oscillator has 22kΩ potentiometers as well as some other, what I would consider harder to find trimpot values. When I breadboarded the circuit, I decided to just use more common values for the pots (I used 100k) and trim pots and it all seemed to work just fine.

Then, this last term in my circuits class, I made the blanket statement that for pretty much any voltage divider, the pot values don't really matter because of the voltage division rule...

We show that Vout is really just a ratio of Vin based on the position of the pot. Unfortunately this is not always true as I found out when I started considering the voltage divider as part of the various circuits it is usually implemented in.

Consider the case when a voltage divider pot is used to scale the voltage of an incoming signal to a simple op amp inverting amplifier/mixer....

If you do the node voltage method to solve this function for Vout, you will find that....

This equation right above tells the whole story. RB (and therefor RP) must be considered with respect to Rin. To understand the equation, lets consider a few cases...

The simplest case is when RB << Rin (note: << reads as "much less than" and allows us to do some mathematical magic to simplify our equation; basically we are going to say that Rin = ∞ with respect to RB).

We can say that RB << Rin when Rin is at least twice as large as RP(the pot value). This math is hardly a "proof" as I skip steps like taking limits. It is only meant to give a feel for what is going on.

From the above, we can say that when Rin is at least twice as large as RP, the circuit works as a classic linear voltage divider (we're gonna show that with a graph in a minute).

Now lets consider another case when Rin = RB. When Rin is larger that Rp, like in the above example, this can never be true. So, now we must assume that RP is larger than Rin

So, this is just a snap shot of when the pot is in a position such that RB = Rin, but we can see that it isn't the same equation as the simple voltage divider. Vout will be smaller at this pot position that it would have been when RP << Rin.

I decided to graph a few different values in wolfram alpha to express this idea. I choose to evaluate this with Vin=5, Rin = 1000, x represents RB,

This first graph is the case when RP is 10 times smaller than Rin. as you can see, the output is very linear.

How about Rp being just half the size of Rin (as we defined in some of the math above). As RB approaches 500, you can see the transition becomes less linear and more exponential (I guess we were a bit liberal with our assumptions.)

Now lets look at a graph where Rin = RP. This exponential response kicks in sooner.

Finally, lets look at the case when Rp is 10 times greater than Rin

Wow, totally un-linear now and it appears to no longer reach 5 volts at the output.

In summation. If you are looking for a linear response, Potentiometer voltage divider values should be chosen such that their value is at least the same if not less than the value of the Rin resistor. So for the Potentiometers in the yu synth oscillator, replacing a 22k pots, it would be better to use 20k or even 10k rather than 50k.

One last thing to consider is the amount of current you are allowing through your pot. replacing a 100k pot with a 100Ω will probably mean much higher power consumption and should probably be avoided. Replacing a 22k pot with a 10k pot should be fine.

Sound activated LED PWM circuit

noreply@blogger.com (Charlie) — Wed, 01 Jul 2015 19:58:00 +0000

Although I've doing a lot of electronics, I haven't written about it in a while. I'm in school for electrical engineering and most of my projects have taken place over 2 or 3 months, so by the time they are finished, it is hard to remember my thought process through the whole project. This project was pretty quick and so it was easy to write about.

This is a simple Sound/voltage Sensitive LED circuit. LEDs are dimmed most efficiently with pulse width modulation. For LEDs, this means turning the LED on and off faster than our eyes perceive while varying the ratio of "on time" to "off time" to change the perceived brightness of the LED. unlike lightbulbs, LEDs have a fixed voltage drop and changing the voltage across an LED does not directly effect the LEDs brightness.

I designed this simple circuit to convert changes in voltage at the input to changes in PWM on LEDs. I achieved this with a 555 and a few op amps. Once I built a the basic Voltage to PWM circuit, it was easy to add a sound input, mic, and "afterglow"(slew circuit). I designed the system but each of the elements were simple circuits that I've encounter in a lot of different analog projects.

Voltage controlled PWM basics:
simple voltage controlled PWM shows up a lot in modular synthesizers. If you have access to a triangle wave (or can create one), you use an op amp to compare a triangle wave to some input voltage(this could be a mic signal). This will create a square wave and the duty cycle (on vs off time) will be dependent on that voltage signal.

Virtual Ground
Because my circuit uses 5 op amps and a simple 12vdc supply (6 op amps including the virtual ground circuit), I opted to build a virtual ground circuit rather than just a voltage divider at each of the non-inverting input. Speaking of all this ground/virtual ground stuff. I spent an few minutes the other day with some 9v batteries and my arduino and a DC adapter and the basic question "when am I allowed(electrically) to connect the grounds of two separate systems. We take for granted that when we plug our headphones output into other circuits, that we are doing just that...connecting the grounds so that the voltage potential between the systems has the same reference. Through my experiments with the batteries, it seemed safe, so long as neither circuit has a reference to the other (electrically isolated through transformers or by being battery powered), you can choose any point in either circuit to equalize as ground reference. For this circuit, incoming signals are reference to the virtual ground.

Getting a triangle wave from a 555:
If you probe around a basic astable 555 setup, you can find that a triangle (or triangle-ish) wave is available from the charging capacitor on the 555. Because we are using PWM in a more qualitative way, it is not necessary for the wave to be a precise triangle wave. If we were really picky, we could use 2 op amps to create a very nice triangle wave oscillator without the 555.

I calculated my frequency using this 555 calculator. In order to get a reasonable triangle wave from the capacitor on the 555, you should shoot for a 50% duty cycle on the 555.

555 calculator

After-glow:
This is a slew-limiter circuit. The diode allows the circuit to only control fall time. When the potentiometer is set to a low resistance state, the capacitor is allowed to fill and empty at a reasonably fast rate. This filling and emptying only happens on the potentiometer side of the circuit because the non-inverting input doesn't sync any current. When the potentiometer is in a high resistive state, the diode allows the capacitor to fill very fast but drain at whatever rate is determined by the resistance of the pot. This essentially creates a controlled "fall time". For the LEDs, it basically means "after glow".

Electret Mic circuit:
This is about the simplest electret mic circuit you can find. The 1M resistor is working as a feedback resistor. Because we are not particularly interested in precision or supplying power, we are using capacitors to separate the DC from AC signal and so we don't need to bias the transistor.

Input Mixer/Offset:
This is the input buffer/amplifier section of the circuit. It takes my incoming signal and adjust it to a reasonable magnitude and voltage range such that it can be compared to the 555 triangle wave. If you've ever worked with op amps as summing amplifiers, you kinda take for granted that the non-inverting input is usually held to ground. One of the best upsides to having the non-inverting input tied to ground, is that you can calculate each arm (or channel) of the mixing amplifier separately and the voltages at the output will add. This is still basically true for the op amp when the non-inverting input is tied to some other voltage but the math is a little trickier. For example, when the non-inverting input is tied to ground, unconnected inputs to the mixer act pretty much like 0v and "fall out" of the node voltage equations. This will become more clear if you sit around doing node voltage on some op amps for an afternoon.

*note that the "kill all positive voltage diode" actually only kills voltage above the voltage drop of the diode, around .7v. We do this because we want our voltage swing to be 0 to -3v and AC signals, depending on our offset value, can end up greater than 0v after the inversion of the op amp.

555 triangle conditioner:
This circuit adjusts our 555 triangle signal into a range and magnitude that will easily be comparable to our adjusted input voltage. I made a note that the original waveform (pictured in the box) has a magnitude of around 5v and is off center from our virtual ground. Again, I did node voltage to calculate my resistor values. I used a 270k resistor instead of the 280k shown in the diagram.

This is the final comparator circuit before which creates our PWM wave. One thing of note is the LED and resistor after the op amp and before the 2n2222 transistor. Because the op amp does not swing "rail to rail", the output from the comparator would never actually turn out because its emitter is tied to -6v and the maximum negative voltage for the op amp is around -5v. The LED greats a voltage drop which eliminates this problem. The resistor which isn't labeled was a 1k.

The node labeled "L" represents the cathode of some series of LEDs (plus a resistor). my LEDs had a 3.2v drop, so I used 3 in series with a 68Ω resistor. Because the 2n2222 can handle 800mA of current and each set of 3 LEDs only draws 20mA of current, I designed my light to use 90 LEDs(30 sets of 3).

Basically, thats it.

MIDI Distributor Redux

noreply@blogger.com (Charlie) — Sun, 07 Dec 2014 18:31:00 +0000

I recently finished my version of the YU SYNTH oscillator, I made quite a few convenience changes to the schematic which I' not totally sure how to write about that. I designed a new PCB and built 4 single width VCOs with those changes.

The panels were made using a subtractive Laser printing (just made that up). Basically I painted the modules black and I used a laser to removed the paint to create the image. because the modules are painted, they are far darker than the etched modules.

I'll have some more to say about these VCOs later.

I recently designed a MIDI distributor module which splits up incoming polyphonic MIDI commands into monophonic MIDI commands on separate channels. I designed it with the intention of turning my modular into a polyphonic synth. I used the Arduino atmega328. I recently rewrote the code to utilize the <MIDI.h> library.

Main code
MIDIbuddy.h

the code uses the MIDI.h library but you also need to add my MIDIbuddy.h file

What I know about etching single sided PCB's

noreply@blogger.com (Charlie) — Mon, 15 Sep 2014 03:23:00 +0000

Because I get so many questions about my PCB etching technique, I decided to dedicate a post to what works best for me. I've divided my advice into a few different sections.

Designing the trace: There's a few things to consider while designing your PCB that will make the whole etching/transfer process more successful. Keep your traces nice and fat. I use Eagle Cad and I try to stick to .032" and above. You can certainly go smaller, but smaller traces are harder to repair if the transfer process results in an imperfect transfer (and it almost always does). Along the same lines, use large pads whenever possible. In Eagle, you can change global pad sizes with the "restring" parameter. Give yourself plenty of space between traces and if you use a "ground pour", make sure the isolation is around the width of a trace( .032" ).

Transfer medium: I use Press-n-Peel blue transfer sheets (search "press peel blue" on ebay). They are prices but I have yet to find anything which can transfer as well as they do. You will need a laser printer in order to print on them. Laser printers use a plastic toner which, when heated, can stick to the copper clad PCB board. Wash your hands with dish soap before working with the transfer. To save as much of the transfer paper as possible, print your design without the transfer paper, cut out a piece of the transfer paper slightly larger than the design, use scotch tape to adhere the transfer paper over your design, reload in printer and print again. cut out the Transfer as close to the design as possible, this is make it easier to place it on the copper. Touch the transfer as little as possible.

PCB material: I buy this stuff off ebay too. Look for single sided using keywords like "copper clad" or "PCB". If you want a flexible or more transparent PCB, try to find something around .030" or thinner. I always prepare the board with a green scowling pad, even if it already appears to be prepared. if you cut the PCB down to a smaller size, you're gonna want to make sure it doesn't have any raised edges, use a file to get rid of them. When my board is prepared, I wash it with dish soap to make sure the surface is grease free.

Heat Transfer Process: I use a griddle to do my transfers but you can use a Iron or whatever. The temperature is very important. I tend to set my griddle to around 270 degrees F. Unfortunately, the griddle is not a precision machine, so you may find that you need more or less heat. Too much heat will cause the transfer image to smear. So will to much pressure. I like to start with the griddle cool.

The transfer is plastic and can collect static, it's good to blow it off before you place it on the copper to clear away any dust that may have stuck to it. For my setup, I place the copper clad material face up on the griddle with the transfer paper face down on the board. Then I place a piece of aluminum over the board to apply pressure. Then I place a book (or a box) on top of that, something of appropriate weight for the amount of surface area the transfer has (I know that is vague but I guess some of this is from practice/intuition). Then I plug in the griddle and wait for the little warm up light to turn off. if you're using something with a heating element similar to a griddle, do your best to keep your material/transfer from being directly over the heating coil.

Moment of truth: After you are sure that the material as reached the right temperature, remove the aluminum/weight arrangement and check out your board. I have this nice little speedball print roller I can use to make sure the transfer as made full contact with the copper clad board. DON'T PRESS TO HARD! After you've done a few boards, you'll get a feel for how the transfer paper looks when it has made a full transfer. Turn off the griddle and use an oven mitt or something to removed the board. I like to cool my board by holding it to the window. When the board is cool, use your finger nail or something to start peeling back the transfer, anyplace where toner was, should be almost completely clear. If, as you are removing the transfer, you notice it has not fully transferred, you can stop and place it back on the heating element and try again.

Making repairs: I've only had a few transfer go well enough to not need any touch ups. Use a very sharp(new) sharpie to touch up any places in which the image didn't completely transfer. This is where having nice large traces can come in handy. There were a few of bigger errors in this transfer because I wasn't careful about blowing the dust off the transfer when I placed it on the copper. If you get any smearing action, or just want to clear up a trace, you can use the tip of a screw driver ( I use a dentist tool ) to scratch away any excess toner.

Ferric Chloride Etching: You can buy ferric chloride at Radio Shack. You'll need a tub of some kind to do your etching. I use a piece of tupperware. Before placing the board in the tub with the ferric chloride, run it under some water and lightly rub/tap your thumb across the surface. This will break any surface tension on the board and allow the etchant to get into all the tiny holes and lines. Now place the board in the tub, pour enough Ferric Chloride to submerge the board. For the next 30 minutes, agitate the Ferric Chloride by gently rocking it back and forth, I use a pencil and make a "see saw." You can tell when the etching has finished when the board is completely transparent in all places not covered by the toner/transfer. Keep in mind that the edges etch before the center.

Cleaning: When your board has finished etching, pour the ferric chloride back into its container. You want as little ferric chloride as possible to end up in the drain. I usually rub clean the board with a paper towel, then rinse it off with water. Now you need to remove the toner from the copper. I like to use acetone to do this.

There you have it! Ferric chloride seems to last for a really really long time. I've done more than 40 etches with mine and it still does the job (even though it's super dirty).

Polyphonic MIDI on a single channel to Monophonic MIDI on separate channels

noreply@blogger.com (Charlie) — Tue, 26 Aug 2014 03:15:00 +0000

UPDATE! 9/19/14 I'm working on a new version of the sketch for this project which uses the midi library.

It's been a while. Since my last post, I've taken two C++ programming classes and hopefully it will show in my coding. I've been working on several projects over that past few months but all of them have been big and though they have working prototypes, they remain unfinished.

I'm working on a simple MIDI controller that works like a flute/guitar. The left hand does the fingering to select a root note and the right hand can "pluck" variations of that root.

combinations of buttons on the headstock choose a root note. for example, when no buttons are depressed, the root note is "E". When only the first button is depressed, the root note is "G". The arcade style buttons on the body actually trigger a note to play. The yellow button will play the root note. The red button will play one step down from the root.

In addition to my MIDI controller, I've been working on a Robot Drummer. This project has entailed building a MIDI to Solenoid "brain" and the actual solenoid drumming mechanisms. I chose to design a simple bracket which screws on to quick clamps that I bought at Harbor Freight. This project also has a working prototype but I am continually finding things that need to be changed/updated.

I have a nice video of this in action

So, I've been working a lot with MIDI lately.

My modular has a pretty simple 4 channel MIDI2CV DAC. I've been wanting to build a new one that could handle polyphonic messages and thus allow my modular to be more polyphonic. Instead of building a whole new MIDI2CV DAC, I thought, as a start, I'd build a little MIDI box that could take incoming polyphonic MIDI and distribute it to a selected number of channels as monophonic MIDI messages. Here is what I came up with.

so, below is all the code needed for the distributor box. because the Arduino IDE doesn't allow you to define a class in a sketch, I had to write my own header/library files. I decided against the MIDI library because I couldn't really understand all the implementation. You can copy and paste the code into text edit or whatever but you need to save the files as charlesMIDI.h and charlesMIDI.ccp, then in the Arduino IDE, past the main sketch into the main coding window and then under the menu labeled "sketch" you can select "add file", then choose charlesMIDI.h and charlesMIDI.ccp.

MAIN SKETCH
charlesMIDI.h
charlesMIDI.ccp

This PCB is different from ones I've done in the passed because I decided to etch the TOP copper instead of the BOTTOM. Normally, components go through the board and and soldered onto the bottom. I decided I wanted components and the copper on the same side. this is why the numbers in PCB image bellow are backwards.

I did a few alterations after I created the PCB. The JP1 in the bottom right corner of the schematic should be collected to the other leg of the priority switch. the diode near the power hook up(bottom left) is a 5v zener diode for power protection. the optocoupler chip is a 6n137. that's just about everything.

Because I have access to a laser cutter, that's how I made the box. I'm not really sure how to post a vector file on my blog so if you are interested in the box, I can send it to you. there is no label for mono-mode because it was an after thought.

Here is a little demo of it working. It's a little bit ridiculous, the size of the box and circuit board I created for this project, but the whole project was a bit of a prototype for other projects in which viewing the circuit board is the focus of the device.

Well, that's all for now folks.

Simple Arduino baby 8 sequencer with reverse and random mode

noreply@blogger.com (Charlie) — Sat, 08 Mar 2014 07:03:00 +0000

UPDATE!!!!! 9/18/14 I did some modifications to the PCB and here it is for those who would like to etch it.

UPDATE!!!! 8/27/14 -- I apologize for the sloppy coding below. It was written before I'd learned any standards for C++. From now on, I'll name variables and functions in a way to indicate how they are used (not after my favorite movie shit). I'll probably do a follow up to this sequencer fairly soon but as I've been using it now for many months, I can say that it has performed flawlessly.

I've been getting into coding lately and so I thought it would be cool to come up with a modular project in which I needed to code. This is a very simple sequencer similar to a baby 10 but instead of using a CD4017, I used an arduino programmed atmega chip. I feel like this project was in the spirit of the modular.

Getting the atmega chip to respond both to clock inputs and reset inputs that are triggered at the same time was the most difficult part of this project. Unlike CMOS chips which respond instantaneously to changes at inputs, the atmega must read each input in cycles. The cycle happens very fast but for things like clock signals in which timing is important, getting the arduino to reliable check the clock input at the correct time is difficult.

In order to "catch" the clock inputs rising edge, I initially put and if statement inside of a while statement like....

While(clock pin is low)

{

if (clock pin goes high)

{ x = x +1;

}

The above general code worked ok but every once in a while, like when the cycles matched up with the speed of the clock, the sequencer would lose a step. I ultimately solved this by using an attachInterrupt();

The interrupt will interrupt the main code to execute code specific to a change to one of the two interrupt pins. I set it to interrupt on the rising edge. I did the same for the external reset input. unfortunately when the external reset and the clock input go high at the same time (which tends to happen often), it is somewhat unpredictable which code will take precedent, either the clock code or the reset code, and for my original code, I would get different results depending on the order. I resolved that by rewriting the code so that it didn't matter which happened first.

int dataPin = 4;

//data pin for shift register

int latchPin = 6;

//latch pin for shift register

int clockPin = 5;

//clock pin for shift register or "shiftout"

int togglePin = 7;

//toggle pin for direction read

int randomEnable = 8;

//source enable pin

volatile byte count;

//4 digit variable

byte countArray[8];

//4 digit array with 8 spaces

boolean reset = 0;

//boolean reset toggle variable

boolean toggleDirection = 0;

//boolean direction toggle variable

volatile int j = 0;

//variable for counting through count array

int k = 0;

int l = 0;

//for making random non repeating

volatile int x = 1;

//variable for counting

volatile boolean bishop = 0;

//create a variable that can be used for clock

boolean hudson = 0;

//create variable used in clock function

boolean hicks = 0;

void setup(){

pinMode(dataPin, OUTPUT);

//set shift register pin to output

pinMode(latchPin, OUTPUT);

//set latch pin to output

pinMode(clockPin, OUTPUT);

//set clock pin to output

pinMode(togglePin, INPUT);

//set reset pin to input

pinMode(randomEnable, INPUT);

//set sourceEnable pin to input

attachInterrupt(0, sigourney, RISING);

//when pin 2 changes (rising edge) move to "sigourney" reset loop

attachInterrupt(1, alienClock, RISING);

//when pin 3 changes (rishing edge) move to "alienClock" clock loop

randomSeed(analogRead(0));

//read analog pin 0 for start of pseudo random sequence

countArray[0] = 1; //0000 0001, step 0

countArray[1] = 2; //0000 0010, step 1

countArray[2] = 4; //0000 0100, step 2

countArray[3] = 8; //0000 1000, step 3

countArray[4] = 16; //0001 0000, step 4

countArray[5] = 32; //0010 0000, step 5

countArray[6] = 64; //0100 0000, step 6

countArray[7] = 128; //1000 0000, step 7

}

void loop(){

if(bishop != hudson){

//limites access to this loop, once per external clock cycle until random is enabled

hicks = digitalRead(randomEnable);

//check to see if random mode is enabled

if(hicks == 1){

//if random mode is enabled then do the following

l = k;

k = j;

//creates a history. k is j last cycle and l is j from the cycle before

do {

j = random(8);

}

while (j == k || j == l);

//generate random value for j and make sure it does not match previous 2 value

}

else {

j = j + x;

// add 1 to j

}

hudson = !hudson;

//prevents function from returning to this loop before another cycle of the external clock

}

//toggle hudson

if(j > 7) j = 0;

//when j reachers 8, go to startpoint

if(j < 0) j = 7;

//when j is less than 0 go to startpoint

}

void sigourney(){

j = 0;

count = countArray[j];

// set count eaqual to present state of starting point

digitalWrite(latchPin, 0);

//ground latchPin and hold low for as long as you are transmitting

shiftOut(dataPin, clockPin, MSBFIRST, count);

//serial output count

digitalWrite(latchPin, 1);

//bring latch pin high to end transmission

}

void alienClock(){

count = countArray[j];

// set count eaqual to present state of j

digitalWrite(latchPin, 0);

//ground latchPin and hold low for as long as you are transmitting

shiftOut(dataPin, clockPin, MSBFIRST, count);

//serial output count

digitalWrite(latchPin, 1);

//bring latch pin high to end transmission

bishop = !bishop;

toggleDirection = digitalRead(togglePin);

if(toggleDirection == 1){

x = -1;

}

else{

x = 1;

}

The schematic is large and hard to read as a single pictures so I broke it down to three.

quad ADSR simplified yu synth ADSR.

noreply@blogger.com (Charlie) — Tue, 17 Dec 2013 01:24:00 +0000

I am an aspiring electrical engineer. Circuit design inspires me in the same way that songwriting once inspired me. In electronics as in songwriting, one often imitates until he can create on his own. When modifying another person's circuit, it's hard to say exactly when one can claim a circuit. How much needs to be different? What kind of changes are considered more than arbitrary and therefore justify claiming ownership (my circuit)?

A majority of the circuits I've worked on for my synth started as either yu synth designs or MFOS designs. The designers of these circuits have far more electronics knowledge than myself and clearly execute a higher level of intention in their circuits. Though I've learned a lot since I began my modular project, I still often find myself in the "shit, lets try this resistor" process. The designs available on these sites are sometimes built upon older designs in which the newer design only varies in peripherals (like input/output buffer impedance, trigger method, resistor value, LED indicator), keeping the core function identical. In all cases, these designs are based on simple electronic processes which were discovered by someone else years ago-- a fact to which these sites openly acknowledge. As participants, we cannot ignore this chain of influence.

I take the postmodern view when it comes to circuit design. No one owns the function in which these circuits are designed to perform. No one owns the function of a filter or the function of an oscillator. These simple electronic functions can be performed in a variety of ways and as we get further away from the tree trunk of an idea, the branches become thinner and closer together. The things I change about these circuits--however arbitrary--make them more suited to my purpose and therefore are as "mine" as anyone's claim to a recipe for homemade nachos.

That being said, I would never directly clone a person's circuit or disregard the chain of influence. I don't believe that is in the spirit of sharing knowledge or creative engineering. In circuit design as in songwriting, my goal is to participate, not "steal"(whatever that word even means anymore).

That diatribe was meant to address the fact that "my" quad ADSR circuit is really nothing more than a simplified version of the yu synth ADSR. By reducing the number of functions it performed and therefore reducing the number of components, I was able to squeeze 2 simple circuits onto a PCB using only 2 chips (quad op amp and LM556). I have no need for an inverted ADSR output because most of the cv inputs on my synth were designed with attenuverters. This ADSR is a sort of a simpler compromise between the two yu synth designs.

This is likely one of the last PCB I will layout in photoshop. The circuit repeats 4 times and so it made sense to do it in photoshop as eagle cad will not allow you to simply copy a section of your PCB layout and stamp it around.

The transistors are 3904's and the collector is the square pad. ha ha. except the very bottom one that controls the led. it's backwards and so the emitter is the square pad. That kind of mistake is easier to make in photoshop. the arrows point to the negative side of the diodes. I doubt anyone will try and build this based on my minimal instruction but posted the PCB just in case. comment any questions, I respond pretty fast.

since I began building modules, I find myself planning more. I like to print version of the panels and lay the components out on them in order to insure that they will fit correctly.

a little DEVO joke for you.

I managed to take a million pictures of my build, except for one showing all the panel wires.

Ms. Twenty module

noreply@blogger.com (Charlie) — Mon, 16 Dec 2013 22:03:00 +0000

The MS20 is a excellent beginner filter because it sounds awesome and there is tons of documentation available for those interested in how it works. Generally when I implement a circuit, I like to find a few different version of it. The MS20 has been cloned about a thousands times and so there are a variety of schematics in which you can compare and contrast component values. I primarily used Tim Stinchcombe's page but I printed and consulted tons of other MS20 filter schematics available online.

There are only a few things which need to be changed in order to switch the filter between lowpass and hi pass functions. I implemented a switch to move between the two functions. The lowpass filter output volume is much lower than the hi pass filter volume so I also incorporated a gain circuit which switches with the filter function.

In retrospect, my method for switching the gain circuit is pretty sloppy and wasn't really seeing the whole circuit when I designed it. The next version would switch the non-inverting buffer at the audio signal input to an inverting buffer, thus the gain amplifier (located at the end of the circuit) could also be inverting (returning it to the correct phase), then I would simply have it switch between two different "Rin" resistors to adjust the gain of the inverting amplifier. There is an audible bleep when switching between filter modes.

also, it is definitely NOT 1v/octave.

I got the boards made at OSH Park. This was one of my first projects in eagle cad. There are things I like about it better than photoshop and things I like less. Unfortunately, when a circuit board has repeating parts, it's next to impossible to copy and past PCB layouts.

Initially I was going to use a picture of Martin Sheen (MS pun) from Badlands on my panel but I couldn't find one that fit the panel layout. In the end, this picture of young Steve Martin (Still MS but backwards) won out. After all of the knobs and jacks are put in, it's hard to tell it Steve but it's still fun for me to know he's on there.

In my earlier modules, I've generally been pretty lazy and just done all my panel wiring in one color. My modules have become a lot complex and so I had to implement the multicolored "twist" method. Since doing so, I do enjoy the final "wire up" process a lot more. less stress.

messing with the MFOS variable state filter -- Sagittronics -- Charlie Slick

noreply@blogger.com (Charlie) — Tue, 17 Sep 2013 01:51:00 +0000

I will start this post with a modular confession. I have yet to utilize, on any filter, the ability for it to act as a sign wave oscillator. I mean, like in a performance, I mostly like to use filters as filters and oscillators as oscillators. That being said, I've been questing for a nice sounding, versatile, simple filter and I don't care so much about 1v/oct tracking.

One of the really amazing things about the MFOS website is that Ray sometimes has the same circuit in 3 different stages of complexity. As a person trying to learn as much as I can about circuits, this is an unmatched resource! I like to look at the early versions of circuits and compare them to the later more complex circuits, to try and understand why things were changed.

Earlier this year, maybe as earlier as February, I built the 12db state variable filter from Ray's "Oldies but goodies" section, on a breadboard. I liked the filter but the filter had some problems. The first problem was that the filter didn't self-oscillate. The second problem is a bit harder to explain. It seemed that when the CV input voltage and Cutoff voltage combine to more than about half a volt, the filter would self-oscillate at a full 30v spread. I likened these problems to the fact that I was using +/-15v rather than +/-12 and could be solved by some small resistor tweaking. I took video of my oscilloscope to demonstrate the problem.

it happens at about 10 seconds in, then it happens a bunch more times.

I was unable to solve the problem then, so I decided to shelve the project for a later date.

After 8 or so months, I figured I'd learned enough to attempt to correct this problem. I assembled the circuit on a breadboard and ran into the same problems. No self-oscillation and whatever you call what is happening in this video.

I toiled over it for a whole day, trying to set a limit to incoming CV but it never truly felt like I was attacking the problem at the source. Finally, right as I was about to give up for the day, I decided to change R27 and R28 to 100k and the problem in the above video went away. I'm not sure how this change affected the topography of the filter but I did notice that the bandpass output got quieter which I can't really explain why.

At this time, I decided to try and implement the darlington transistor pair inside the LM13700 that Ray mentions trying to integrate on the "oldies but goodies" page. I guess I wanted to simplify the circuit even more and I was in a general electronics exploration mood. He presents a circuit in the MAKE: Analog Synthesizers book that unitizes the transistors in this way, so I had a nice guide to work from.

I was able to to do it, but not without some trouble. I now had the opposite problem, when the incoming CV and Cutoff voltage was so low that it turned of the Darlington transistors, causing the outcoming voltage to swing all the way to -15v. I solved this with the 2m2 resistors connected to ground, they are intended to keep the transistors on. I'm sure this affects the 1v/oct tracking but again, I can't even get the filter to self oscillate.

In the end, I'm not even really sure what I have here. I ended up with a similar circuit to the one in the MAKE: Analog Synthesizers book but with a Hi-Pass Filter and slightly more precise CV input.

I'm not happy enough with the circuit to build a module, and I'm so burned out on it, I can't tell if it even sounds good anymore. I guess I will shelve it again for a while and let the ideas stew. I did benefit from toying with the filter in my attempts to tame/simplify the design. Comment with any suggestions. I guess I'm moving on the the YuSynth Steiner filter next, or perhaps this MS20 design I found.

Attack Decay LOG LIN Gate controlled Portamento --Ziggy Stardust Rise and Fall module

noreply@blogger.com (Charlie) — Tue, 17 Sep 2013 00:55:00 +0000

This circuit is primarily based on a Harry Bissell design. I changed some values in order to make the input impedance 100k and I added a gate controlled switch, which I borrowed from the YuSynth portamento. The comparator circuit to control the LEDs which indicate the state of the portamento was my own design. This circuit allows you to adjust Attack slide separate from decay slide. It also allows you to adjust the portamento between linear slope and a slope resembling logarithmic.

above is the schematic. I know you are probably thinking, when is this guy gonna get a fucking scanner? I'm sorry, I'm broke right now.

I'm not gonna spend a lot of time how how to assemble this one. For me, I got lost somewhere along the assembly. It was just too complex and I had to rewire a bunch of connections I made. In the end, I can't remember what I got right and what I got wrong on my PCB labels. With 12 panel mounted knobs, 12 jacks, and 12 leds, it made for a lot of hook up wires. Below is the PCB without labels for hook up wires, to be amended at a later date.

So, I started etching aluminum with Copper Sulfate instead of Ferric Chloride. From what I've read, it's safer and better. I like it better too.

this is my class transfer griddle, I was attempting to make a nice transfer press out of it. It will eventually happen.

basically, you mix equal parts Copper Sulfate with table salt and add that to water. My solution was very strong because I basically mixed in as much as I could get to dissolve into the water.

This is a 2 bath system. Copper Sulfate on the left and just regular water on the right.

I believe what happens, is the copper and aluminum trade places. The copper leaves the copper sulfate mixture and solidifies, while the aluminum takes its place in the mixture, becoming Aluminum sulfate.

Super Simple Linear Asymmetric Portamento -- Glissando -- Slew Limiter -- Glide

noreply@blogger.com (Charlie) — Fri, 30 Aug 2013 19:24:00 +0000

FYI, this is not the schematic for the Attack Decay Gate controlled portamento I just built, I will be posting that build/schematic very soon. Thanks! (that schematic incorporates aspects of this schematic, so if you're at all into understanding analog circuitry, this post will help you understand the upcoming post)

I just finished designing a far more comprehensive portamento module but I'm waiting on a few parts in the mail to complete it. While that's brewing, I thought I'd take the time to show an extremely simple and awesome linear portamento circuit. It's similar to a portamento modules I worked out in an earlier blog post, this one has the proper resistors to give it a 100k input impedance and a 1k output impedance which I find ideal for modular synthesizers.

For those who don't know: Portamento, glissando, glide, and slew limiter are all different names for the same musical concept. It's basically sliding between notes. Since Modular synthesizers are analog, their "musical note information" is represented by a voltage between 0 and 5v instead of a digital number.

An overly simplified example: a C note might be represented by 1v and a D note might be represented by 1.5v. If we wanted to slide between these notes, we would alter the rate at which it the circuit could move from 1v to 1.5v. We do that with an RC Circuit. The R and C are resistor and capacitor.

The two main types of portamento circuits for modular synthesizers are exponential(logarithmic) and linear. For linear portamento, the slide time is dependent on the difference between the voltage(note) values. There is a longer slide time to get from C to G than from C to D.

In exponential portamento the slide time is not dependent on the difference between voltages(notes). The slide rate is based on internal resistance, so it is consistent no matter the distance between voltages(notes).

The circuit below is linear portamento. There is a potentiometer labeled 1M in the middle of the circuit. This is the main R in the RC circuit and determines the amount of portamento. The more resistance we add with this Potentiometer, the more portamento we get. By adding a switch and diodes, we give can voltage a path through a diode and around the potentiometer. The diodes allow either positive or negative voltage through dependent on it's orientation. This gives us the ability to have slide only on ascending notes or only on descending notes

The left side is the input and the right side is the output.

Parts
2 X 100k resistor
2 X 1k resistor
1 X 1m potentiometer

2-3uF non-polar capacitor
2 X diodes 1n914 variety or similar will work
1 X spdt (center off) switch

2 X op amps. either 2 X 741's or a single TL072 or half of a LM324 or whatever

I've tested this circuit on a breadboard and it works great but I didn't build a module based on it. It's simple enough that it could be easily done on prototyping board. ENJOY!

AttenuVCA mixer -- Auto Panner --Simon Pegg

noreply@blogger.com (Charlie) — Sun, 18 Aug 2013 23:11:00 +0000

I recently moved to Portland,OR from Ann Arbor MI. A little before the move I was working on a newer version of my 10 step sequencer but I ran into a bunch of problems and although it turned out OK, I won't do a post on it until I get it figured out completely. That being said, my first project after my move was to build a simple 4 Channel VCA to replace my earlier VCA.

There were a few things I wanted to improve on the older, modified MFOS VCA I built. I figured it would be cool to design in a simple Mixer circuit to allow the module to be used as voltage controlled mixer. I also thought it would be nice to be able to invert the individual channels CV so I could use the module as an auto panner or subtractive VCA. To accomplish this, I include attenu-verters on all the inputs. The VCA I designed is mostly based on the MFOS VCA and the VCA that Ray put in his MAKE book, which came out this year. I decided to skip the whole LIN/LOG aspect of the VCA and just make it a simple LIN VCA. This kept the overall circuit much less complex.

There is a mistake in the schematic above. the NPN transistor was switched out for a PNP. the LED connects positive side to ground and negative side (shorter) to the emitter of the PNP. the collector is connected to -15v via a 2k4 resistor. the base is the same, connected via a 100k resitor to pin 7.

the build...

I never know how much time I should spend explaining how to assemble this stuff because I'm not sure that anyone actually builds it besides me. Below is the etchable PCB and a PCB Parts layout. One thing that is not on the PCB parts layout is the 4 x 3906 PNP transistors, so there are four sets of 3 open pads near the bottom. these are for the PNP's. The square pads are collectors.

The panel mount pots are all 50k. The leads that should be soldered to the circuit board are labeled on the PCB. For example, on the volume pot, the CW(clockwise) and C(center) pads are labeled. the remaining pot pin CCW (counter clockwise) should be grounded. same goes for the inverter pot, CCW and C are labeled, the CW pin should be grounded

I used switching jacks for the Input and the CV input. I connected the jack in such a way that if you plug an audio source into channel 1 and nothing in channel 2, then the signal will be repeated in channel 2. the same goes for the CV input relationship between channel 1 and 2. I also wired channels 3 and 4 this way. Makes it easier to use the module as an auto panner.

the four separate VCAs are arranged in columns on the PCB.

There are 3 trim pots per column. the near the bottom, (50k) is for adjusting the attenuverter. use an oscilloscope connected at the output of the attenuverter to compare the normal signal versus the panel mount pot all the way left and all the way right. they should have equal amplitude, adjust the trim pot accordingly. *pin 7 and GND or 8 and ground on the TL074 are where you should connect your oscilloscope depending on which VCA you are trimming

The middle trim is to set the DC offset of the CV input on the VCA. plug an audio source into the input. leave the CV input unconnected and make sure the panel mount volume knob is all the way left. connect your oscilloscope to the output. adjust the trim pot until the audio source just barely disappears.

The top trim pot is used to adjust the DC bias of the output. leave the oscilloscope connected to the output. disconnect the audio source from the input and adjust this trim until the oscilloscope reads 0 volts.

do this for all the channels.

I forgot to mark the polarity on power supply capacitors below. the left one is negative towards ground and the right one is positive towards ground. that should be everything.

I did a Panel layout with Simon Pegg. if you want to etch it, consult my earlier blog posts about etching aluminum. the image below will need to be inverted and flipped horizontally for etching. the PCB above is ready to transfer.

These are some photos from the process.

I was using an iron to do my transfers but I recently started working with a presto griddle. It will eventually be more like a sublimation press but that's a project I'm still working on. The griddle is an excellent heat source though.

This isn't my best panel etching. The ferric chloride was very fresh and etched a lot faster than I anticipated, that being said, it still turned out cool and gave Simon "zombie eyes" which isn't out of theme from the picture, which was borrowed from Shaun of the Dead.

I came up with an idea to use those like right angle brackets for soldering all the wires and panel parts.

After I finish soldering, I can remove the brackets and mount the panel without much fuss to the stand off bolts.

And finally, here's a video of it in action.

Rick Moranis 10 Step Baby Gate Sequencer module based on the CD4017

noreply@blogger.com (Charlie) — Fri, 31 May 2013 04:13:00 +0000

I Just finished my newest version of the "baby 10 sequencer". It has control voltage and gate switches. I found some problems with it, and subsequently this module. I will be posting some modifications in the next few days.

In preparation of improving my baby 10 sequencer, I've been coming up with things to do with the CD4017. A couple weeks ago I built the sub-oscillator out of the CD4017. That introduced me to the 2 transistor Schmitt Tigger which I borrowed from the Yusynth clock divider. I also borrowed from that same clock divider, a diode "and" gate which I modified for this project. I also chose to incorporate a "gate to trigger" circuit similar to Ken Stones Gate to tigger circuit for my reset sync input. I'm not sure how much of this module you could actually call mine, but I guess this is how you learn at first. Working out this circuit will be a big help when I move onto my all encompassing 10 step baby sequencer. possibly my next project.

I did a mock up on a breadboard of my idea to make sure they would work. here is a video.

then I drew up a schematic incorporating all these different ideas

I came up with a cool idea too as I was trying to do the panel layout. I hate rotary switches! they are expensive and I find them to be panal hogs. There just wasn't enough room to incorporate all the inputs, outputs, switches and LEDs I wanted in a single module width while still having that clunky 10 position rotary switch. So I came up with an idea of using a SPDT(on/off/on) switch to control the gate as well as the reset. the positions work like this (gate one/gate off/ Reset). One thing to be noted is that having more than a single switch in the reset position will cancel the reset out. This could be fixed by adding diodes but I felt that would be mostly unnecessary and would add 10 diodes the PCB, when really, all you have to do is not have 2 switches set to reset at the same time (something you don't have to worry about with a rotary switch)

I'm also proud to say that this single sided PCB layout has no jumper wires!

parts....

1 X CD4017

1 X TL072

1 X 741

4 X NPN transistors ( I used 3904s)

7 X Diodes 914s or 4148s

10 X SPDT (on/off/on) mini toggle switches

11 X LED's

4 X 1/4" jacks

1 X .0015uf cap

2 X 22uf Cap

12 X 2k4 Ω

3 X 1k Ω

1 X 15k Ω

3 X 22k Ω
~~1 X 220 Ω~~ 100Ω

1 X 47k Ω

8 X 100k Ω

2 X 10 Ω

1 X 4k7 Ω

I guess they only thing I really have to clarify is how the switches and LEDs are wired. The "switch&led sends" should be connected to the center of the SPDT switch. the Positive leg (longer leg) of the led should be connect to the bottom switch lug (so when the switch is in the up position, it connects the LED and switch send) and the top switch lug should be connected to the "reset return". I panel wired all the reset turn lugs together. The negative side of the LED should be connected to the "switch&led returns" bank. Then of course the labeled outs and ins should go to their designated 1/4" jacks. The last LED is the final gate LED which is labeled on the top centerish of the PCB. that should be connected to the positive side of the LED and the negative side to ground.

I did this kinda fun .gif of me designing the PCB. I changed a couple things from this version to the final PCB layout which you might notice if you look carefully.

These PCBs are ready to etch, print them and transfer them.

I noticed that an extra hole ended up on the PCB just below the right side of the diode on the left bottom, ignore it.

For the panel layout, I went with Rick Moranis because I'd just watched Ghostbusters. if you want to etch this, you should flip in horizontally and invert it in photoshop.

And last, a video. ENJOY!

Square wave sub oscillator based on the CD4017

noreply@blogger.com (Charlie) — Tue, 21 May 2013 02:58:00 +0000

Wouldn't it be cool, to be able to mix in different sub-octaves of a frequency, similar to an organ or my old Korg poly800, without using up a bunch of oscillators? NOW YOU CAN! This module is in the realm of wave folders and saw tooth animators. an oscillator augmenter.
I got an idea of how to do that with the CD4017 when I was looking up schematics for building a Gate sequencer and a clock divider.
Essentially, how the module works is, you feed it a very high frequency from an oscillator. it creates a square wave version of the original signal and the 3 octaves bellow it. you can access any of the signals directly, or mix them via potentiometers to a mixed output jack.

Below is a schematic I drew up that shows the basic idea. This schematic only shows one sub-octave, not all three.

below is a drawing I made of the schmitt trigger used in the Yusynth 4017 clock divider. I used the same basic set up in my module also.

Below is some notes I made when working out which pins should be connected to each op amp. I also made a note to put caps on the outputs to keep the DC current from leaving the circuit.

This is the PCB I came up with. I threw in a picture of Brock Samson for good measure. most of the inputs and outputs are labeled on the pcb. The Transistors have "c"s on the pcb to indicate that is the pad for the "collector". The three unmarked pads in the center of the PCB are for the 100k trimpot used to offset the the square waves to make them AC signals. On the left near the bottom are the outputs for accessing each sub octave separately(the leads with the caps), and the sends for the mixer pots (the 10k resistor)

The pots (and pretty much all volume pots) should be wired with the "sends" coming off the 10k resistors the the Center of the pot. CCW pot lug should be connect to ground and CW pot lug should be connect to one of the pads labeled "return" on the PCB.

Below is a picture of my test circuit. usually these test circuits don't include all the features of my eventual modules, just what I need to make sure works....

This is a little video of me testing the circuit.

Now for some etching.

You may have noticed that this PCB has a lot of jumpers. Having a bunch of jumpers in your PCB looks hackneyed but this was the best I could do without having the PCB be double sided.

I created a panel design also, which I etched. this is lenna. If you want to etch this, make sure you invert it and flip in horizontally in photoshop, otherwise, it won't turn out like mine....

I didn't do a great job show how useful this modules is in my video. It makes a really awesome bass sound, like of like nintendo sounding.

All finished. email me with any questions.

Midi2CV module via Midimplant board

noreply@blogger.com (Charlie) — Fri, 26 Apr 2013 17:26:00 +0000

UPDATE 8/19/13 -- I'm working on a new version of this module with buffered outputs. Stay tuned

This is a module I built based on the Midimplant board. They are capable of different configurations which you can upload via midi Sysex. The website has a configuration widget here, which makes things incredibly easy. One of these options will convert midi to CV and Gate signals for 2 independent midi channels. My eventual goal is to have a 4 channel midi to CV module, so I hope to be getting another board when they are available. With that in mind, I designed the module and the PCB to be ready for my future configurations.

Here's the board. I soldered a header on it, to make it easy to play with.

Here's the pinout. Something to keep in mind, is the gate signal is whatever the Positive voltage input is. my system is a standard Synthesizers.com/motm +/-15V. All my modules seem to work fine with 15v gate, so I didn't really worry about adding a voltage regulator, but it would be easy to implement if that was a requirement.

I like LEDs on everything. Why else build a big monster synthesizer if it's not going to be covered in tons of blinking lights. I added simple 3904 LED buffers to the circuit aswell.

I didn't do a schematic and I didn't label the pads on the parts picture either but I will name the now.

It's clear where the chips go. the chip should be facing you.

LEFT SIDE of the PCB

Midi input (pin 4 and 5 on your DIN jack) it doesn't matter which of the 2 pads on the PCB.

RIGHT SIDE of the pcb

(from top to bottom)

CV2

LED2

GATE2

Gate1

LED1

GND

CV1

(chip 2)

CV2

LED2

GATE2

Gate1

LED1

GND

CV1

It should be set up so that the thru is already connected correctly to the second chip's midi input, but I am unable to test this because I only own one chip currently. You will need to configure the chips seperately using the first chip socket.

The artwork from this module is a nod to Twin Peaks. I also did a front panel design.

I use a more diluted mixture of Ferric Chloride for etching Aluminum. basically I mix in the same amount of water as etchant (I got this etchant at radio shack). I have no idea if etching aluminum is toxic or not, wear a resperator if you are considering this. I leave it in there for about 5 minutes.

Korg Mono/poly polysix SSM2044 Low Pass Filter chip module

noreply@blogger.com (Charlie) — Fri, 12 Apr 2013 03:48:00 +0000

UPDATE!!! 8/19/13 I'm not sure how I feel about this project. I've had the module for a while now and I'm not a huge fan of the end result. I guess it is what it is.

I've owned a Korg Mono/poly for 8 years now. It's an excellent synthesizer and I've never been to compelled to buy any other expensive analog synth because it's such a workhorse. I was thinking about selling it recently, because All I ever play these days, is my modular. I thought it might be cool to build a filter module based on the filter chip inside the Mono/poly--the SSM2044. Did a quick google search and found these plans.
You can find these chips for like $20 on ebay and I thought that was a minimal investment for a fun project. I ordered one and some other parts. Like all projects, I breadboarded it first to make sure it worked. I had a hard time finding a tempco 1k PTC thermistor. All I could find was NTC thermistors, so I used one of those. That was probably a mistake. I finally found some PTC 1k thermistors which I ordered today. When they come, I will replace the NTC.

So, this wasn't the most satisfying of all projects. The first thing I didn't like was the range of the Cutoff knob, so I played with that for a while. I also didn't like how the Resonance knob only seems to kick in--in the last 30 degrees of rotation. I messed with values and I just kept getting farther and farther from a solution. I realized later that it probably has more to do with the fact that I was using a log pot instead of a linear.

I did some more research and turned up a few more values to try, which is the primary source of the modifications above. A modification that I made, which I was surprised hadn't been made before has to do with which input you use on the SSM2044 chip. It has a + signal in and a -signal in. I determined that the - signal in was an "inverting input". I chose this to be the main input because there is an inverting amplifier on the output. This makes the output signal the same phase as in input signal. I also switch out the 150k resistor for a 120k. I did this because I was having a horrible time trying to tune the thing to a 1v/oct. I never really got it to a place I was happy with, but it's good enough I guess.

I also chose to use attenuverters at in the CV inputs for both the Cutoff Frequency and the Resonance level. I found the basic design for it on another Fonitronik design. I sketched it out for my own purposes below.

I designed a PCB for the whole project, which you are welcome to use, or you can use the one on Fonitronik

Alright, lets go over some of these labels.

TOP LEFT

QCV: resonance attenuverter input

CW: resonance attenuverter clockwise pot pin

Center: resonance attenuverter center pot pin (the CCW pin is grounded)

TOP RIGHT

CCV: cutoff attenuverter input

CW cutoff attenuverter lockwise pot pin

Center: cutoff attenuverter center pot pin (CCW pin is grounded)

ALL THE REST

OUT: filter ouput

Qcenter: Resonance pot center

QCW: resonance pot clockwise pin (CCW pin is grounded)

180 in: inverted input

1v/oct: 1 volt per octave input

Freq center: Cutoff pot center pin

Freq CCW: Cutoff pot counter clockwise pin

FreqCW: cutoff pot clockwise pin

In: regular input (CW pin of input attenuation knob, CCW to ground)

Therm: 2 points to connect thermistor

Setting the trim pots can be tricky. you need a duel channel oscilloscope to set the trim for the attenuverters. connect a sine wave or triangle wave to the attenuverter input. connect one channel of the scope to the same signal. clip the leads to the other channel on ground and pin 7 of the TL072 for resonance, then pin 1 for cut off. adjust the trim pots so that the inverted signal is equal in amplitude to the source signal. I would consult Fonitronik or the rest.

Here's some pictures of etching and assembly. The transfer turned out really good.

As you may have seen in other posts. I've started etching my aluminum front panels. This project has ben Total Recall themed.

and finally a video. enjoy.

Simple MFOS LFO & Acid Etched Front panel

noreply@blogger.com (Charlie) — Mon, 01 Apr 2013 03:30:00 +0000

After all the trouble I was having with the 8038 Chips, I decided to build a new LFO module based on a different design. Early on, I tried building the MFOS super simple dual LFO but I couldn't get it to work. I decided to try it again, now that I'm better with electronics and it worked fine. In retrospect, the mistake I made the first time-was most likely my interpretation of the schematic. Notice the inverting and non-inverting inputs on IC1-D and IC1-A are flipped, so if you are not looking carefully, you may wire them incorrectly.

I always breadboard my projects first and especially when they might need to be modified because they supply voltages are different. This schematic worked well but I changed a few of the values based on what kind of components I had around. I changed out R7 with a 20k resistor to bring the square wave output up to +/-10v, so I can use it as a clock signal. I changed R90 to a 2k4 resistor because I didn't have any 3k resistors. I also changed out R8 with 1K resistor because when the frequency knob was at it's farthest left point, the wave would stall out, I don't know if this had something to do with using +/-15v vs +/-12v.

I made my own PCB for it, but I'm not going to share it because the one on MFOS works perfectly well. I only did mine because I like the challenge of creating PCB layouts and I wanted to use a 1m and 2m resistor in series instead of a 3m because I didn't have any around. I also wanted the LEDS to be connected to the triangle wave because I think it looks cooler to have LED's fade on and off instead of just be on or off.

There was another thing I really wanted to try with this project. I've been acid etching PCBs for a while now, and it seems like a cool idea to acid etch a front panel too. If you're only creating one or 2 modules, the idea of going through the whole process of creating a silk screen seems like a waste of time and money. I made the layout in photoshop just like I do my PCBs. I did a nice halftone of Sigourney Weaver from Alien.

I used steel wool on the aluminum panel before I did the transfer. The transfer process was extremely painstaking, I had to go back with the iron several times and reapply the transfer. I also burned my fingers trying to pick up the panel in order to hold it against my window (a method I use to rapidly cool it off).

I put it in a nice big tub and went all willy nilly with Ferric Chloride. One thing I learned was that Ferric Chloride works a hell of a lot faster on aluminum than copper. It kinda freaked me out the way it starting fizzing and spewing out(probably poisonous)gas. The container got really hot too. I found that if I ran around my yard with it, shaking the tub back and forth, it kept the bubbling down-and it seemed like it might not explode into flames. After about a minute, or at least I assume, I dumped the whole thing out in my yard and sprayed it off with hose.

I was almost positive that it didn't work, but after I washed it off and rubbed it with steel wool again, I realized, IT LOOKED AWESOME!!!

I think next time, I will thin out the acid with a little water and leave it in the acid for a shorter amount of time, like 45 seconds or something. Down near the bottom, it over etched a little, but it still turned out really cool.

I drilled all the holes and put the parts on and it looks great!

Here's some photos of me assembling my PCB too

Those two circled points are mistakes I made in my PCB design. Luckily I noticed them early on and it didn't take much to fix them.

I use angled aluminum for my mounting bracket. I had to cut and file this one down a bit in order to make it fit between my components.

Here's a video. It's the module on the top right.

"Gate keeper" MorphLag Portamento and envelope generator

noreply@blogger.com (Charlie) — Mon, 25 Mar 2013 02:16:00 +0000

UPDATE!!! 8/19/13 I just finished a newer version of this module. I changed some component values and ended up with a better version of this design. I also added in a gate activated on/off switch. it will be posted soon.

I was super excited when I found the Schematic for this simple but versatile portamento circuit. I Had an idea similar to this, a little while back when I was building the Ian Fritz AD/AR generator. I noticed then, even the Fritz AD/AR was similar to a simple lag circuit, and it put the idea in my head for a simple portamento with seperate controls for up(attack) and down(decay) slide. Nerds will notice right away that this can also be used as a simple envelope generator.

The original circuit can be found here. Below is the version I printed and made some modifications to. Also, I clearly spilled coffee on it. Since the schematic already used three op amps, I decided to go ahead and use a forth for the indicator LED, which is probably unnecessary, but turned out really cool. I thought it would be cool to have one led correspond to the attack and another correspond to the decay. I tried a differentiator op amp set up, comparing the input voltage to the output voltage. That schematic is in the bottom right hand corner.

I breaded it up and everything worked great except for, when the shape knob was at its most ccw point. It was doing this weird self oscillation thing. I rectified that by adding a 240Ω resistor.

I also added a bypass switch.

I design my PCB's in photoshop. I've been playing around with inserting pictures in the background of my PCB's, and I guess it's kinda my thing now.

PARTS:

1x LM324 (or any quad op amp)

2X 22uF electro caps

4x 1uF Tantalum caps (or any other higher value non-polar)

4x 1n914 diodes (or any switch diodes)

2x 10k pot

4x 1M pot

4x 1/4" jacks (6 if you include the inverted output)

2x spst switch (4 if you include the "long" switch)

4x regular leds

Resistors

4x 10k

5x 50k

6x 100Ω

4x 100k

4x 470k

2x 240Ω

2x 1k

4x 20k

This is a Dual circuit.

I used 1uf Tantalum caps in my circuit because I had a bunch laying around, but you should be fine using any larger non-polar cap. I put an option in for adding a "long" switch, which would add more capacity and give you longer slide time but I ultimately found it unnecessary, but still the option is there. My final module has two 1uF caps for each of the two circuits. I also skipped the inverted output jack because I ran out of room on my module face.

I'm not gonna spend a lot of time explaining how the pots should be wired. if you can't figure it out by the schematic, then it's a skill you should learn. For the attack and decay pots, you add lag by adding resistance, so you'r going to want to solder one point marked "A" on the PCB, to the CCW pin of the pot and the other point marked "A" to the S (center) pin of the pot. Do the same for the Decay. The bypass switch points are labeled "b" on the PCB for bypass.

so, I've been doing this transfer thing for a little bit now and I get my best results when I use steel wool on my copper first. Also, don't have the iron on too high. I set the iron to just barely higher than the "polyester" setting. Even when I get a really good transfer, I still usually have to do some minor touch ups with a marker.

I also have this method for doing the acid bath. I put the board in a shallow tupperware container, add the acid, and put a pencil under the container. Then I use my finer to tip the container back and forth, causing the acid to wash over the board in a regular motion. I usually have a fan on too.

Try it, it work pretty well.

nothing to adjust once it's built. if you're super worried about tuning over several octaves, I'd use 1% resistors. I didn't, and I noticed the CV for pitch get's a little skewed at the far end. Call it character.

there's the PCB

Hit me up with any questions or if you spot any faulty information. I am an amateur. Here's a video of it in action. You're probably gonna want to full screen it, if you want to see the LEDs in action.

4017 "baby sequencer" 10 Step Sequencer

noreply@blogger.com (Charlie) — Thu, 21 Mar 2013 21:21:00 +0000

UPDATE 6/1/13!!! After playing with my sequencer for a little bit, I've noticed some stuff I'd like to change about it. A redesign in the near future which will include a switchable gate almost identical to the Gate Sequencer I built around the 4017 in this post. I also noticed that you need to convert the incoming clock signal to a very very short square wave, I am probably going to use a "gate to trigger" circuit similar to ken stones, which I think is basically a differentiator. Otherwise when the square wave (clock signal) falls from High to Low, the output voltage of the 4017 changes just enough to make the notes flat. expect a newer design soon!!

This is my first attempt at a sequencer. It's built around the 4017 Decade counter chip. It's my first foray into using CMOS's chips (unless you count the CMOS 555 in the ADSR). The design I came up with is an amalgam of the Baby Sequencer and various sequencers on MFOS. I was trying to get away with as little circuitry as possible. This version of the sequencer doesn't include a gate output. So you can sequence control voltage only, you can't skip steps. My plan was to build a seperate gate sequencer, which I thought would stretch the 10 steps farther.

I did a mock up of my design using little trim pots, just to test the basic concept, it seemed unnecessary to do this for all 10 channels.

So, it's really straight forward design and I never even made a schematic for it. I went straight from breadboard to PCB. so, I don't have a schematic to show you, but the PCB is incredibly easy to follow, so we'll work from there. Read the whole post before you build anything.

Parts list

1x CD4017

1x TL072

10x 3904 NPN trannies (or equivalent)

10x 100k Pots

1x 50k Pot

2x 1/4" jacks

1x Rotary switch (10 or 12 position)

2x momentary switch (you want ones with a throw, not just open and closed)

22x 100k resistor

10x 680Ω or 1k resistor

1x 10k

1x 100Ω

2x 10Ω

2x 22uf electrolytic cap

100K POTS: Lets start with how the pots should be wired. I found this little picture online so I can refer to the pot pins without people getting confused. The pot output from the board for each channel should be soldered to the CW of each of 100K pots. The Center pin (labeled S) should be wired to one of the many returns above (the returns are all the points with 100k resistors, it doesn't matter which one, they all get mixed together). the CCW pin should be soldered to ground.

50K POT: you need one 50K pot for the "Scale Knob". Solder the CCW pin to one of the two scale pins on the PCB. Solder the Center Pin to the other point. Doesn't matter which one.

LED: The LED point on each of the Channels should be soldered to the positive pin (longer pin) and the Negative side to GND. I listed 680Ω resistors, but I ended up using 1K resistors with green LEDs.

next up is the clock input and reset and all that junk. this can get confusing.

CLOCK: Solder clock point from the board to the tip of a 1/4" jack, with Gnd to Sleeve. I found later, that depending on what you use for a gate signal, you may want to solder a diode from sleeve to tip (positive end toward ground and negative end to tip), this will stop all negative voltage from flowing into the clock. So, if you use a square wave from an oscillator as a clock signal for example, it will eliminate the negative crests, which I noticed causing the CV voltage to change when the wave swung from positive to negative.

RESET: Solder a wire from the CW pin of each channel pot(except for channel 1) to a pin on a 12 or 10 position rotary switch (in order), any remaining points on the rotary switch should be soldered to ground. Solder the common pin of the rotary switch to the Reset point on the PCB.

OPTIONAL RESET BUTTON: you can also add a push button if you'd like to be able to reset the sequencer with a button. Disconnect the Common pin of the rotary switch from the Reset point on the PCB and Solder it to the Normally Closed pin of the momentary switch. Solder the common pin of a momentary switch to the reset point on the PCB. Solder the +15V point from the PCB to the Normally Open point of the switch. essentially, when you push the button, you disconnect the rotary switch from the Reset point on the PCB and Connect the Reset Point to +15v, causing the sequencer to reset.

CLOCK ENABLE: This allows you to pause the sequence. Connect the Clock Enable point on the PCB to the common pin of a momentary or toggle switch. Connect the Normally closed pin of the switch to Ground and the Normally open pin to +15v.

In retrospect. i think it would be nice to have a reset input. that would be added in parallel with the reset button, but with a diode to keep voltage from flowing backwards through the rotary switch to the channels.

let me know if you noticed any mistakes. I am a novice.

Here's a video of it in action with my yu synth wavefolder

and here's the PCB

8038 Triple LFO module

noreply@blogger.com (Charlie) — Wed, 06 Mar 2013 19:18:00 +0000

I would avoid building this module. I ran into so many problems trying to find 8038 chips that I liked. I decided instead to build a different BETTER LFO module. that post is HERE. If you have some 8038 chips laying around with the correct numbers on the, then, this could work for you.....

I recently built a pretty simple but very useful LFO circuit with the ICL8038 chip. I decided to go ahead and build a triple LFO module in a double wide panel. I took the time to make a nice PCB for the circuit with fat traces and solder pads. When I finished and assembled my module, I was surprised to find that two of the three circuits didn't seem to be working correctly. They had a limited range. after checking all my traces, I realized that the two which were not working correctly were newer chips from a different batch/seller. The one that was working was from the first module I built. ultimately, I decided that the different chips did not work with my circuit.

this chip works with the circuit
ICL8038CCPD
P0306BDVZ

and this chip doesn't
ICL8038CCPD
P1106BDVZ

I tried ordering more chips with the correct numbers based on the picture of the chips on ebay and they sent different chips that didn't work. I'm really annoyed with the 8038 chip situation. So, I'm going to revisit this LFO project with a different circuit, one that doesn't utilize the 8038.

So, go figure. Anyway, here's the PCB. I'm not going to spend a lot of time explaining this circuit because I did so in an earlier blog, HERE

So, I've included the single LFO parts reference because it explains the how to wire the two potentiometers.

The triple LFO is on the right hand side. In the center is my sequencer which will be included in the following blog.

YuSynth ADSR module

noreply@blogger.com (Charlie) — Wed, 27 Feb 2013 18:05:00 +0000

So, A little while back, I built the Ian Fritz dual AD/AR module and it works pretty good but after using it for a few weeks, I decided to upgrade to full ADSR modules. I have an ADSR envelope generator from Synthesizers.com but my goal with this project is to teach myself stuff and eventually replace any ready built modules with ones that I've put together.

I can't link directly to the project page because of how their website is set up, but you can find it on YuSynth by navigating through a few menus. If you are going to build this module, you will find the all the necessary information on that website including PCB's and component layout. Consider this blog post, like a DIY builders epilogue.

I built the improved ADSR module and in fact, I actually built two of them into one double wide module. why not do two individual ADSR modules? well, double wide modules have more space than two single wide modules because they share two edges. They are also more rigid, and since I'm only using simple panels instead of module blanks, that's also a benefit. I also have limit power plugs and this way, they can share a power plug too.

I breadboarded this schematic before I built it and it's a good thing I did. because, or at least with the components I used, the LED didn't seem to work. I tried a few different resistors but it was only after I tried switching the orientation of the Diode and the LED (D5 & LD1) that the led worked. I'm not sure if this was a mistake in the Schematic or just circumstantial, but anyway, its work just fine now, reversed.

There was one modification I made to the PCB before I etched it. In the instructions, there is an optional 150K resistor which changes how the inverted output works. it essential shifts the inverted output into positive voltage, subtracting from +10v instead of 0V. I decided to put in another junction allowing for a switch, to switch between these two options.

So, here's the PCB I ended up etching. It's a dual and it has the mod for the switch I mentioned above. You will find all the component placement and stuff like that on yusynth, as well as the original single module PCB. My modification is in the bottom left corner of each of the two circuits. the two holes closest to ground in that corner are for the switch.

BE SUPER CAREFUL ETCHING THIS PCB! because the 3 traces that go under the CMOS 555 chip are extremely close together, I had to scratch away a little between the traces and put it back in the acid to make sure they weren't connected, this is where having an LED pen light can come in handy, making sure traces are not connected.

when transferring I always double check all the traces to make sure they are nice and solid, I fix whatever looks weak with a sharpie. They make etch resistant markers, but this seems to work fine. I also like to fill in big open spots, so there is less to etch.

Laying my stuff out on the panel to make sure it will all fit nice.

When my spots are all chosen, I tap them with a nail and a hammer so they don't get erased. then I circle them with a marker and label them. Makes drilling the holes to the correct sizes harder to screw up.

Then I choose the placement of the PCB and put those holes in.

now for the build.

I know other people use jumpers and connectors and crap, but I just solder my wires directly on, I ain't got money or time for all those jumpers. Something I've learned to do though, is prepare all my wires before I start soldering. By that, I mean, cutting them to the correct length, stripping them, and tinning them if need be.

by the end of a bigger build like this, my patience gets worn down as well as my soldering iron. I pretty much went start to finish on this project but it's more likely a two day project. I find it helpful to change tips often too. I use a file to make them nice and pointy again, or I just put a new one in.

When I finally finished this project at 11pm last night, the left ADSR worked great and the right one didn't! OH NO!!!! I went back over everything, checking all my pot and switch connections. It still wasn't working. Then I went over the PCB with an LED again to make sure nothing was making accidental contact. I found a hair thin piece of solder connecting to pads, I scratched it away and it worked great! BE CAREFUL and dont panic.

THINGS TO KNOW FOR THIS PROJECT! definitely use a CMOS555 chip and not a tradition 555. I used Tantalum capacitors for C7 and C8 like the instructions said but I tested it with Electrolytic caps when I had it breadboarded up and it seemed to work fine. DOUBLE CHECK ALL YOUR TRACES, especially under the 555.

a little demo.

Ultra Simple 8038 LFO circuit & PCB

noreply@blogger.com (Charlie) — Wed, 20 Feb 2013 18:58:00 +0000

UPDATE!!!! I recently built a triple LFO version of this build and ran into some problems with the new set of 8038 chips I purchased, they don't all work the same, The amazing range I got were specific to my first batch of chips. keep your eye out for this set of numbers, because they worked.
ICL8038CCPD
PO306BDVZ

and the following set of numbers did not work with this set up.
ICL8038CCPD
P1106BDVZ

I tried ordering more chips with the correct numbers based on the picture of the chips on ebay and they sent different chips that didn't work. I'm really annoyed with the 8038 chip situation. So, I'm going to revisit this LFO project with a different circuit, one that doesn't utilize the 8038.

For my modular project, I'm trying to keep it simple, at least in the beginning, so i can learn what I can from each circuit I build. A simple LFO circuit, is something I've tried to build a few times, with limited success. It wasn't until I was clicking around on YUSYNTH (my new favorite website. It's loaded with projects and information), that I came across this ultra simple implementation of the ICL8038 chip.

I wired up the circuit almost exactly how it is here and it worked pretty good, But I didn't have the necessary switch for all the cap and resistor combinations--which led me to experiment with different combinations of resistors and caps to cover the range I wanted. I put in a 1uF Tantalum cap at pin 10 and a 1M pot (replacing R5, R6, & R7) and was able to achieve the ultra low oscillations I was looking for. The 1M Pot basically working as a Coarse tune, and the 10K pot working as a Fine tune. I also found that the voltage input was basically useless to me, it seemed to hardly affect the frequency and when i hit it with higher voltages, it would stop oscillating altogether. I decided to skip that aspect of it, at this time anyway.

Theres some extra chips on there because I was testing to see if the square wave output would work as a clock for the a 4017 decade counter chip. it does.

Above is the schematic that I came up with and ultimately built into a module.

Electronics is one of those things, where I don't exactly understand, at what point you can call a circuit "my circuit". I mean, how much do you need to change and does it really matter if you're giving away the plans for free. Anyway, I felt like I changed enough to call it my circuit, but it's really just a modified version of the circuit I found on Yusynth.... It's like a remix

I decided to just draw the PCB.

I made a little mock up of the traces

I thought it might be easier, especially with the chip, to drill the holes first, using a perf prototyping board to set the spacing. I guess that helped, though drawing little traces with a fat tipped permanent marker can be kinda stressful.

I realized, after I started etching the pcb, that I forgot to put the transistor rate indicator on there, so I added that. Strangely, I found that drawing on the partially acid etched board was easier, and the ink stuck to it better, probably because the acid made the surface less smooth. It made me consider dipping my boards in acid for a second before I apply transfers to them also. who knows?

The board came out good and so i put the components in there.

In the end, I opted for a switch between Sine and Triangle waves. The square wave gets it's own output, so I can use it as a clock.

KICK ASS!

so, I spent some time this weekend and made a PCB in photoshop which everyone is welcome to use. let me know if there are any problems with it, because, I hand drew mine. It's designed to be transfered, so you should be able to read the writing correctly after it's transfered.

So, things to know about this circuit. Both the .1uF cap and 1uF cap are bipolar. The Transistor is a 3904 but you can use an equivalent NPN. You can change the 680Ω resistor that is connected to the transistor according to the LED you choose. The negative side of the LED should be connected to ground (I panel wired all of that stuff). I forgot to mark the orientation of the two 22uF caps, but that's something you should be able to figure out. The left cap is for the positive rail, it should be oriented with the positive side of the cap connected to the rail and negative side to ground. The right cap should be opposite, positive side to ground and negative side to negative rail. You will probably need an oscilloscope to tune the 3 trim pots. you may be able to do it by ear. One of the 100k pots is responsible for offset, adjust it to center the wave over ground. the second 100k is for shaping. The 100Ω is also for shaping, do that one last because it's more of a fine shaping. The shape of the wave changes depending on what frequency was when you set the trim pots, as you get farther away from that frequency, the waves begin to distort. I set the trim pots to be most accurate when the LFO was at lower speeds because that's when you'd be able to hear it most clearly. so, the wave becomes a little mis-shaped at high frequencies.... enjoy.

In the video, I have the 8038 LFO hooked up to the cut off frequency of my Synthesizers.com State Variable Filter. Enjoy.

MFOS VCA for MOTM +/-15v take 2!

noreply@blogger.com (Charlie) — Fri, 15 Feb 2013 21:23:00 +0000

You may want to consult my earlier blog about the MFOS DUAL VCA. I wasn't totally happy with the results from that build, so I went back and made better, more informed modifications to the circuit.

I don't want to take credit for doing anything except changing some values to get the circuit to perform better with my +/-15v system. If you're at all interested in building this circuit, I suggest you start by checking out the original VCA on Rays website. There you can find the earlier version for +/-12v along PCB layouts for etching.

This is the circuit and the values I ended up using for the VCA.

These changes gave gave both Log CV and Linear CV similar volumes, which was a problem I was having with the original circuit. It also brought the overall output volume up in the range of my Synthesizers.com VCA which was nice.

Somewhere along the line, I accidentally used a 220K for R18 instead of 220ohms. I didn't notice until I hooked it up to my Oscilloscope to compare it to my Synthesizers.com VCA. Basically, The mistake over drove all the incoming signals and turned all my waves into Square waves. After hunting around, I found my mistake and fixed it. It goes to show, that not all mistakes like that, will make the circuit totally un-useable. Sometimes those simple value mistakes can take a little while to manifest.

Variable Inverting to Non Inverting OP AMP amplifier

noreply@blogger.com (Charlie) — Thu, 07 Feb 2013 18:53:00 +0000

This is a pretty simple but useful circuit I put together. It's basically a variable inverting/Non-inverting amplifier. When the pot is all the way left, the signal is Non-inverted. All the way right, it's inverter. the center has no output. I designed the circuit to mimic a property on my Synthesizers.com State Variable Filter module. From I can tell, it works exactly the same. I was surprised when I tried searching for an op amp set up that would do this, I couldn't find one. I probably just don't know what its actually called. Anyway, here's the design I came up with.

I used a 741 to test it out.

In this video, I used it on my Filter with a triangle wave. as you turn the knob, the signal attenuates all the way to 0, which is about center, then it begins inverting

MFOS Dual VCA (Quad VCA) module for MOTM

noreply@blogger.com (Charlie) — Fri, 01 Feb 2013 23:13:00 +0000

UPDATE!!!! 2/13/13
I recently took another look at this module and did some more adjustments to it, the following blog was written during an in between stage. You may want to look ahead in my blog for a more current version of this build. HERE

Basically, the best resource for getting started in building Modular Synthesizers is Music From Outerspace. Most of my modules came from this site, as well as a bunch of core ideas I applied to other modules. The only thing that can get in the way with building modules from this site, is, most of the schematics are for a +/-12v power supply. My Modular is the MOTM style with +/-15v. a lot of the projects are scaleable and don't require any modifications but some do. The next project has a couple small modifications I made to the MFOS dual VCA project which I found, made it better for a +/-15v system. REMINDER: I am an amateur and I don't guarantee anything.

so, if you feel inspired to build this circuit, I encourage you to visit the MFOS page where you will find more information and PCB layouts for the project.

So, like all projects, I breadboarded it up first and tried it out. It worked well but there was a huge volume difference between Log and Linear CV response. Also, I own an Synthesizers.com VCA and it had a noticeably lower volume over all. using my Synthesizers.com VCA as a standard I decided to mess with the resistor values and see if I couldn't get a similar volume. Well, as you can see above, Ray actually made some modifications to the circuit in red, and I thought, not knowing exactly what I was doing, I would try reverting those values back to their orignal values to see what effect they would have. At least then , I could understand how they improved the circuit. I Found that going back to the original values for R15 and R16 gave me more overall volume. I liked that. R18 I left at 220ohms and R14, I ended up using a 27K resistor because it's what I had.

I still had this problem with the volumes between the modes being really different. so I played with some of the other resistor values trying to make this better. It occurs to me now, after looking at the schematic again, I would approach this problem differently. What I ended up doing was changing out R9 from a 120K to a 1K. That allowed a lot more current through and brought the volume up. If you've got this schematic breaded up and you feel like trying some stuff, I would try changing the R3 and R4 to 10K resistors and see how that affected the circuit. I wouldn't be surprised if I wrote another blog about this circuit in the future with other changes.

Overall, the circuit works quite well, so I went ahead and etched 2 of them into a pcb to make a quad version of this module.

I built this handy circuit board holder for the project. Made soldering a whole lot easier. I pretty much always use those chip sockets because my soldering iron doesn't have a temp control and I've been known to burn up chips in other ways too.

Making sure my parts would all fit on my double wide panel

I decided to add some leds to my amplifier. flashing lights make everything cooler. I built this simple 3904 led buffer circuit on a hand drawn PCB. basically, the Base of the 3904 is connected via a 100k resistor to the signal output of the VCA circuit. and the correct resistor value for the LED of your choice should go between the collector and +15v, and the LED should go between the emitter and ground. I always use a heat-sink when soldering transistors

I didn't have enough spdt switches, so I've got one dpdt switch in there.

I added a jumper area to the left of the original layout. I found it's nice to have all the wires leave the circuit board from the same area, makes things cleaner but also adds to the work. That's also where I've got my power hook up (top left)

All finished!!!

This video is on the boring side, but I didn't really know how to effectively show the VCA in action without becoming convoluted with the operation of other modules. so basically, I change the envelope on 3 channels and also switch between Log and Linear VCA.