Theremin World Recent Forum Posts

Can’t turn off post notifications? (by trymeinchesss)

You could always just have your gmail or whatever block emails from theremin world. I don't know if that is what you are looking for but if you can't find anything else I'm sure it will work.

Can’t turn off post notifications? (by clararox)

My husband had been using my account (since he got locked out of his device after our home caught fire) and was trying to contact Jason to update/change his password because he never signed out of his account and so had forgotten it. Somehow he must have subscribed to post notifications where he’d been posting using “clararox” and I’m still receiving them in my email even after he has stopped using my account. There aren’t any settings that I can find to turn them off. Should I just change the email for this account to his?

Let's Design and Build a (mostly) Digital Theremin! (by André)

Hi,

Today, I just finished the translation of the D-Lev user manual in FRENCH.
You can find it on the support page of the D-Lev site.
Direct link

Je viens de terminer aujourd'hui la traduction en FRANÇAIS du manuel de l'utilisateur du D-Lev.
Vous le trouverez sur la page support du site D-Lev.
Lien direct

Let's Design and Build a (mostly) Digital Theremin! (by dewster)

AFE Progress

I've been futzing around with the AFE circuitry again and feel like I've made some progress.

Above: The schematic. The stuff on the left is my rail-to-rail buffer, the middle is the coil and antenna, the right is attenuation, filtering, and squaring of the quadrature and in-phase signals that go back to the FPGA.

In particular, it would be highly desirable to roll off high frequencies from the antenna to the quadrature output, and this is supplied by R2/C2, R3/C3, and R4/C4. High pass filtering is supplied by C1/R1. The difficulty in doing this is obtaining a flat-ish phase response around the nominal operating range of the coil and antenna resonance. Previously I tried more or less identically filtering the in-phase leg to match the phase response of the quadrature leg, but this lead to excessive attenuation of the in-phase signal. I got the idea that all we really care about is matching the phase response around the operating zone, and after a bit of messing around with the simulation I found the simple C6/R6 high pass and C7/R7 low pass combo was entirely sufficient to do this, and with very little resulting attenuation.

Above: AC analysis from the coil drive to the quadrature filter output. Resonance is clearly around 440kHz, with significant roll-off on either side. Note the notch at ~1.4MHz.

Above: AC analysis from the antenna to the quadrature filter output. +/-3dB @ 55kHz / 4.2MHz; -10dB @ 10MHz; -47dB @ 100MHz; -16dB @ 10kHZ; -35dB @ 1kHz.

Above: AC analysis of the in-phase filter output (top red) and quadrature filter output (bottom green). You can see here that the phase responses of both overlap from 1kHz up to about 1MHz.

Above: AC analysis of the combined responses, again showing no phase deviation up to about 1MHz.

In simulation, the coil LC resonance Q is reduced by approximately 5% compared to the previous simple capacitive divider. Some Q reduction is to be expected due to the presence of the quadrature filter resistors, as they dissipate electrical energy as heat. 5% is negligible and a very good tradeoff.

Above: AFE circuit running on the bench. Breadboard is at the "cold" end of the 8mH coil, "hot" end is connected to a piece of aluminum flashing material. You can see the string of 10pF caps running down the center axis of the coil. So far, this super messy setup is running quite stable, even with scope probes attached.

How does it perform in real life? I've had it running on the bench now for several hours this morning, and it is very stable and very quiet in terms of phase noise - probably the best I've seen of any oscillator I've tested. It could just be that today is quiet in terms of environmental RF and ground noise, so I'll keep it going for a few days and report back. If all goes well, the main unresolved issue would then be how to adjust the amplitude of the quadrature filter output - I'm thinking of a few 10pF caps on the AFE PCB in series with the 10pF axial string that could be shorted out via jumpers.

[EDIT] A frequency dependent phase difference between the two legs can likely cause issues. The obvious one is reduction in antenna voltage. If the phase difference is non-linear then one would probably also worry about this impacting the linearity of the pitch field, though I'm not sure how to quantify that.

[EDIT2] If I touch the plate with a finger the DPLL locks to 1.5MHz, which is 3x the nominal. I believe this corresponds to the anti-resonance notch in the second image. The bad part is that it says locked there until I power cycle it. This is likely aggravated by the fact that the FPGA is running a load optimized for the smaller inductors. I need to extend the lower range and see if that helps. Some kind of false lock detector in the DPLL circuitry would be nice, but I'm unsure how to implement that without interfering with normal behavior. I think limiting the low end of operation is a mistake.

[EDIT3] Today, 24 hours later, the DPLL phase remains super quiet, so it seems filtering is a keeper. Playing around with touching the plate, it remains correctly locked with a slow press of my thumb. A quick press causes the 3rd harmonic lock. So it's not the range limitation that causes the false lock, it's the gestural bandwidth of the DPLL not tracking a really fast change in capacitance. I'm currently looking into ways to sense and recover from false lock situations.

Let's Design and Build a (mostly) Digital Theremin! (by André)

Problem: she doesn't speak english! Maybe her boy friend does...

Let's Design and Build a (mostly) Digital Theremin! (by dewster)

"Today I updated the front panel of my nr 1 which will soon become the property of Charlotte Dubois." - André

Sweet! Please let Charlotte know that I'm always available for field setup and such. It would be nice to meet her too.

Let's Design and Build a (mostly) Digital Theremin! (by André)

Today I updated the front panel of my nr 1 which will soon become the property of Charlotte Dubois.
It look like nr 2 doesn't want to let nr 1 go...

Let's Design and Build a (mostly) Digital Theremin! (by dewster)

Thanks much for the pix André! I went ahead and posted a couple of them to the D-Lev web site. Your build is really beautiful, inside and out!

"In fact, what is important is the distance between antennas." - André

True that.

"the volume antenna is located in the middle of the left side."

Not saying you should, but if you similarly located the pitch antenna, the unit would then be 100% ambidextrous.

"Again, thank you Eric, for this wonderful instrument and for your help!"

My pleasure, I very much appreciate your skilled involvement in this project!

Let's Design and Build a (mostly) Digital Theremin! (by André)

Here are the pictures: My D-Lev nr 2

And the prototype: My D-Lev nr 1

As you can see, the prototype was tilted 22.5° on its tripod for better visibility of the display.
(Why 22.5° ? Because the PL259 antenna connectors have positioning increments of 22.5°.)
In fact I don't like it because the audience can only see the bottom of the instrument and its retractable feet. Not very pretty.

Finally, the display and the LED are perfecttly visible when the instrument is flat.

The enclosure is made of teck wood (recuperated from a boat deck).
The front plate is covered with a special cloth used in book binding (called "Relon" in french).
The D-Lev logo is laser engraved on the cloth. I wasn't sure how the cloth would react. It's looks surprisingly good.

About the size of the enclosure, I tried to make it as small as possible for transportation.
Eric, you said that the wider width of Carolina's unit is somewhat non-ergonomic for her.
In fact, what is important is the distance between antennas. Carolina's build is larger but the pitch antenna is installed in a hole of the front plate.
On mine the antenna is on the right side with a PL259 connector and a 90° bend with a radius of 50 mm. So the antenna is probably around 100 mm to the right, compared to Carolina's.

Another difference with my prototype : the volume antenna is located in the middle of the left side.
This allows me to play farther from the instrument.

Again, thank you Eric, for this wonderful instrument and for your help!

Let's Design and Build a (mostly) Digital Theremin! (by Trymeinchesss)

Stop making me jealous with that museum!!! Next time I’m over in that part of the states I’ll have to check it out.

Let's Design and Build a (mostly) Digital Theremin! (by dewster)

"I was inspired by Carolina's but it is more compact. 440 x 190 x 90 mm. I think her's is (are!) about 100 mm longer." - André

Good, I believe the wider width of her unit is somewhat non-ergonomic for her.

"I will post more pictures when it is fully functional."

Yes please! Then I'll post them to the D-Lev site (if that's OK with you).

"Well, I decided I couldn't sleep without solving the problem. There was a transistor leg not soldered. Shame on me!"

Yay!

Let's Design and Build a (mostly) Digital Theremin! (by André)

Looks really beautiful!

Thank you. I was inspired by Carolina's but it is more compact. 440 x 190 x 90 mm.
I think her's is (are!) about 100 mm longer.
I will post more pictures when it is fully functional.

It made its first sound today, thanks to your great help, Eric!
I had eeprom initialization problems and Eric help me out with patience and a lot of back and forth mailing.

Now I have to understand why the display back light doesn't work!
Tomorrow is another day. It's 9:30 PM here.

Edit: Well, I decided I couldn't sleep without solving the problem.
There was a transistor leg not soldered. Shame on me!

Let's Design and Build a (mostly) Digital Theremin! (by dewster)

"I like the sofa!" - André

I thought it was pretty cool too!

"Sweet couch, Eric. You feelin’ any oscillations or them ‘Good Vibrations’ with your booty?" - ILYA

No booty action whatsoever!

A better view of it, it's a "miniwoouf":

There's a nice painting of Bob above it:

Even the front door mat has a synth theme going:

The allowed pictures to be taken in the gift shop, but not inside the museum proper, though you can see a few on their web site.

Let's Design and Build a (mostly) Digital Theremin! (by dewster)

"Almost finished my second D-Lev." - André

Looks really beautiful!

Let's Design and Build a (mostly) Digital Theremin! (by ILYA)

I like the sofa

Sweet couch, Eric. You feelin’ any oscillations or them ‘Good Vibrations’ with your booty?

Let's Design and Build a (mostly) Digital Theremin! (by André)

Some life but not much...

I contact you by email.

Let's Design and Build a (mostly) Digital Theremin! (by André)

Almost finished my second D-Lev.
I don't expect any hum problems since it is fully identical to my first build, except the case!

Will come to life tomorrow morning...

Let's Design and Build a (mostly) Digital Theremin! (by André)

I like the sofa!

Let's Design and Build a (mostly) Digital Theremin! (by dewster)

Moogseum

Back from vacation, we hit the Moogseum in Asheville, NC:

The best part was reading Bob's biography via the touch screens. Many of the interactive exhibits could use some TLC. Two Etherwaves to play with, only one sorta in tune, the knobs were behind Plexiglas. A video igloo thing that didn't respond very well to the knob twisting. A couple of Minimoogs to fiddle with in the back that weren't really Minimoogs. There was an Ethervox on display, as well as some of his very early units.

Nitpicking aside, it was definitely worth the pilgrimage, particularly so if you find yourself near the area!

Let's Design and Build a (mostly) Digital Theremin! (by dewster)

"I thought it was good to let you know that all Prozor's are not equal." - André

It is good to know, thanks!

The V2.2 looks like it has fewer components around the output driver, not sure what that means. The PROZOR DACs I buy have a volume control on the side, yours appear not to. Looking inside, there is an inductor near the input power jack that is populated. Some have reported hum issues, and there is a hum problem on the unit I just built. It seems hooking the DAC power to the D-Lev power causes it? I can use an external stereo line level isolation transformer to get rid of it, but that impacts low frequencies at high volumes. I never experience hum when powering the DAC and D-Lev via separate AC chargers.