DIY Audio Projects - Hi-Fi Blog for Audiophiles

Hi-Fi Chip Amplifier (chipamp) with TDA2050

2009-07-05T11:48:00.005-05:00

Thomas from Germany has put together a build log of his recent DIY TDA2050 Hi-Fi Chip Amplifier (chipamp) build. The chipamp project is built around a single chip - the TDA2050V integrated circuit (IC) which is produced by STMicroelectronics. The TDA2050 chip is capable of producing about 25W of output into 8 ohms with 24V power supply rails. Like most chipamp projects, the circuit is very simple and can easily be constructed on perfboards.

The power supply is also constructed on a perfboard. For the power supply Thomas uses a 120VA torroidal transformer with dual 18V secondaries and generally followed the "snubberized" Gainclone power supply design by CarlosFM with 10,000 uF per rail.

For the enclosure Thomas used a Hammond satin black steel 12" x 8" x 3" chassis (Model 1441-24). The amplifier controls including a headphone output are on the front.

Thomas reports that the chipamp produces very good sound and that the small amp can hold it own against various high quality amplifiers that he has used. For complete project details, see the DIY TDA2050 Hi-Fi Chip Amplifier (chipamp) page.

These chipamps are simple to build, low-cost and when properly implemented can deliver very good fidelity. If you are looking for a project to try out, give one a try.

Additional Chipamp / Gainclone Projects:

Mark's Nano LM3875 DIY ChipAmp (gainclone)
Bruce's LM3875 DIY Chip Amplifier (Gainclone) Kit
Mark's LM3875 Gainclone Chip Amplifier in a Roasting Pan
Gio's LM3886 DIY Chipamp Project Kit
Mark's Point to Point LM3875 Gainclone / ChipAmp instructions

What's Playing: Natalie Mechant - San Adreas Fault

Prototype Boards for DIP Chips (op-amps)

2009-06-14T21:57:00.013-05:00

There are several printed circuit board (PCB) manufactures who cater to hobbyists by offering small quantity orders of PCBs. Some of the larger manufacturers offer free PCB design software that makes it very simple to come up with your own PCB designs. This is all great until you see the price estimate for that pair of simple boards can be in the order of $50 to $100US. Well, when I am spending that much money on parts it is generally for vacuum tubes, an enclosure or perhaps a transformer - a simple PCB, no thanks! Fortunately for simple circuits a prototype board (protoboard) will often suffice and they are generally inexpensive and commonly available. This post examines some of the low cost protoboards that are available for use with an integrated circuit (IC) that comes in a dual in-line package (DIP) - such as an operational amplifier (op-amp).

The noted costs are from 15 June 2009
Dual General-Purpose IC PC Board - Radio Shack 276-159 - ($2.49US)
This general purpose board is perforated and can be split into two pieces. Each piece will accept up to a DIP20 package or a couple of smaller DIPs can be fit on a board. The overall dimensions are 1-3/4" x 3-3/8" and when split apart each board measures 1-3/4" x 1-3/4".

The board is constructed from phenolic which is generally flimsy, but given the small size of the boards that is not an issue. Be careful when mounting using the screw holes as it is easy to break a corner off the board. The board is easy to work with but the small size will limit it to small projects. One problem with the board is that the solder pads are fairly thin and as a result with rarely survive desoldering and re-soldering if you need to make changes to the circuit.

What is nice about the boards is that they are often locally available and their low cost. The boards are available from Radio Shack in the US for $2.49US:

Dual General-Purpose IC PC Board - Radio Shack Catalog # 276-159

Here are a couple of DIY Audio Projects that use the boards:

Mark's CMoy / Grado RA1 Headphone Amplifier
Mark's DIY Op-Amp Hi-Fi Preamplifier

Multi-Purpose PC Board - Radio Shack 276-150 - ($1.99US / $4.99CDN / $2.96AU)
The Radio Shack 276-150 is a popular multi-purpose protoboard. The overall dimensions of the protoboard are 1-7/8" x 2-7/8" (48 x 73 mm). There are 417 holes on the board and up to a DIP50 package or a few smaller ones can be fit on the board. Two traces run down the center of the board which can be used for grounding or power rails.

Like the previous Radio Shack protoboard it is also constructed from phenolic. On the 276-150 board the mounting screws are very close to the edge and it is very easy to break a corner off. Also, the solder pads are thin and will lift off the board if too much heat is applied. The boards are a good size and very easy to work with. There is plenty of space to get three DIP8 op-amps on a board.

These boards are very common and available in the US ($1.99US) , Canada ($4.99CDN) and Australia ($2.69AU):

DIY Audio Projects that use these boards:

CMoy Mint Tin Headphone Amplifier

D-4 Prototype Board - audioXpress PCBD-4 - ($4US)
Darren of DH Labs was kind enough to send us a sample of his prototype board design. The board measures about 2-1/4" x 3-1/4" and can hold a DIP50 package with space left over. A ground trace runs down the center of the board and there are also two power supply traces on either side. The board is constructed from fiberglass and the pads are tinned.

With the ground and power traces the D-4 Prototype Board is ideal for use with op-amps. There is plenty of room to fit up to four DIP8 packages on the board. The fiberglass construction and distance of the mounting screws from the edge make it unlikely that the corners will break off when mounting. The soldering pads are fairly durable and will survive desoldering and re-soldering if you need to make circuit changes. Considering the cost of the 276-150 boards in Canada, the switch to the D-4 boards is an easy one for me.

The D-4 Prototype Board is available online through audioXpress ($4US):

D-4 Prototype Board - audioXpress Item# PCBD-4

The photo below is a DIY Phono Preamplifier that Darren put together using the board.

Please let us know if you have a favorite protoboard that you use with op-amps.

What's Playing: Rebecca Pidgeon - Grandmother

OddWatt Audio - Tube Amplifier Kits

2009-06-08T20:03:00.008-05:00

Our friends Bruce and Rodney sent a message informing us that their website - OddWattAudio.com is now active and that it should be fully functional in the next few days or so. Some of you will will recognize the term "OddWatt" which is the name Bruce gave to his scalable push-pull amplifier projects. The DIY versions of the OddWatt tube amplifiers are documented on the DIY Audio Projects website and are listed below.

The OddWatt tube amplifier project pages provide full details of the amplifiers as well as instructions on how to build the amplifier.

The OddWatt circuit is failry simple and consists of a SRPP driver stage which feeds a self-inverting push-pull (SIPP) output stage. The output stage operates only in Class-A mode and the bias is set using a LM317HV regulator that is configured as a constant current source (CCS).

Currently OddWattAudio.com is offering KT77 and KT88 OddWatt amplifier kits as mono-blocks. However, their website indicates that stereo EL84 OddWatt kits should be ready around July. The OddWatt site also indicates that a stereo preamplifier and a headphone amplifier kit may be available in the future. Photographs of the KT77 and KT88 tube amp kits are shown below.

Photograph 1: OddWatt - OddBlock KT77 Push-Pull DIY Tube Amplifier Kit Parts

Photograph 2: OddWatt - OddBlock KT88 Push-Pull DIY Tube Amplifier Kit Parts

The photos below show a the finished OddWatt KT77 and KT88 tube amplifier kits.

Photograph 3: OddWatt Audio - OddBlock KT77 Push-Pull DIY Tube Amplifier Kit

Photograph 4: OddWatt Audio - OddBlock KT88 Push-Pull DIY Tube Amplifier Kit

Photograph 5: OddWatt Audio - OddBlock KT88 Push-Pull DIY Tube Amplifier Kit

The finished mono-block kits look great. Based on the information on the site, the kit comes complete with all the parts required to build the amplifier. I've been meaning to build an OddWatt amplifier for some time now so the timing was good and I placed an order for a pair of KT88 mono-blocks last week. My kits should arrive in the next few days. When they do arrive I'll post an update complete with photographs.

Cheers,
Gio

What's Playing: Tracy Chapman - Give Me One Reason

DIY Hi-Fi Cable Projects

2009-05-19T21:23:00.004-05:00

We have added a couple new DIY Hi-Fi Audio Cable Projects to the website.

DIY Belden 89259 RCA Cables
A couple of weeks back we added detailed instructions that were put together by our friends at auDIYo.com to construct the popular Belden 89259 line-level RCA interconnect cable design by Jon Risch. The cables are a simple unbalanced RCA interconnect cable design that uses the high-quality and low capacitance Belden 89259 coaxial cable. Through the use of TechFlex Expandable Sleeving, shrink wrap and good male RCA plugs, a novice can put together a very nice looking set of Hi-Fi interconnect cables that will deliver the performance and not set you back a few hundred dollars. For full details, see the Belden 89259 DIY RCA Interconnect Cable project page. The photo below are DIY Belden 89259 RCA Cables put together by Paul from Kent, UK. Click the image to enlarge.

DIY Low-Inductance Speaker Cables
We have also added instructions to construct simple DIY low-inductance speaker cables. Adam has put together these fine looking speaker cables for his DIY 3-Way Hi-Vi Tower Loudspeakers. The cables are very simple to construct and consist of plain 16 gauge wire that is twisted together in alternating directions. The alternating cable geometry results in a speaker cable that has a very low-inductance and the equivalent wire gauge 10 and thus the cable resistance is also low. For that Hi-Fi finish, Adam uses a set of high-quality gold plated banana plugs, TechFlex Expandable Sleeving and a custom laser etched decorative oak sleeve. The results are a sharp looking speaker cable that rivals the performance of commercial speaker cables at a fraction of the cost. For full instructions, see the Low-Inductance DIY Speaker Cable page.

What's Playing: Roy Orbison - In Dreams (live)

Coldplay - Left Right Left Right Left [2009]

2009-05-16T11:20:00.008-05:00

While not DIY, I thought I would let you guys know that Coldplay is offering a free album download.

Quote from Coldplay.com:

"... The free download of Coldplay's new live album, LeftRightLeftRightLeft, is now available here on Coldplay.com ...

Today [May 15, 2009] is also the day of the band's first North American tour date, in West Palm Beach, where the first copies of the LRLRL CD will be given away.

The CD will then be handed out to all fans at every remaining Coldplay live show in 2009 (apart from Festival shows). The free download will also be available from Coldplay.com until the band play their final 2009 show."

The download is a 54.5MB .ZIP archive containing 9 .MP3 tracks which are recorded live. The MP3 tracks are 192 kbps and sure they are not the pinnacle of sound reproduction, but it's music and FREE.

Here is the link to download Coldplay's Left Right Left Right Left live album [54.5 MB].

Track Listing:

Glass of Water [4:43]
42 [4:52]
Clocks [4:40]
Strawberry Swing [4:16]
The Hardest Part / Postcards from Far Away [4:15]
Viva La Vida [5:24]
Death Will Never Conquer [1:39]
Fix You [5:38]
Death And All His Friends [4:22]

The images of the album cover are and a screen shot of the track information is included below. Click on the images to enlarge them.

What's Playing: Coldplay - 42 (mp3)

DIY Lightspeed Passive Attenuator

2009-05-11T19:40:00.005-05:00

Alps Blue Velvet, Bournes, TKD, Alps Black Beauty, DACT Stepped Attenuators ... If you are familiar with some of these names, you likely have an interest in high quality passive attenuators and you should continue reading. The noted items have a few things in common - first off, they are potentiometers that are often used as attenuators or volume controls in audio equipment. As a volume control, they also have another thing in common - they all used some form of "contact point" to attenuate audio signals. In the case of a potentiometer, this is typically a "wiper" which slides along a conductive material forming an adjustable voltage divider. If you are passionate about audio reproduction, you are fully aware that these "contacts points" can be the source of unwanted noise. Now it certainly does not make sense to spend money on high quality interconnect cables only to run the signal through a dirty potentiometer that you infrequently spray with with a contact cleaner like Deoxit.

When people talk about the "sound of capacitors" someone will inevitably say that the best sounding capacitor is "no capacitor" - that is if it can be eliminated. So following that principle, one could argue that the best sounding attenuator is one with no contact points in the signal path. Enter the Lightspeed Passive Attenuator.

The Lightspeed Passive Attenuator uses optocouplers to establish the level control and this is done with no "contact points" through the attenuator. The optocoupler is a LED and Light Dependent Resistor (LDR) is one housing. The operation principle of the Lightspeed is simple - by adjusting the intensity of the LED you can change the resistance of the LDR. By using a series and shunt combination of matched optocouplers the attenuator produces a constant input and output impedance, regardless of where the voltage control setting is. Hmmm, an attenuator with constant input / output impedance and no contacts points - great idea!

Uriah has put together a detailed set of instructions to build a DIY Lightspeed Passive Attenuator. I've built one of the attenuators for myself (photo below) and I think it's great! It is a remarkable improvement over all the passive potentiometers that I have tried. The attenuator is very simple to build, so if you have an interest in higher quality volume controls take a look at the instructions.

The attenuator design could easily be scaled upward to include support for multiple channels and used as an effective way of controlling several of channels for a Home Theater setup. For full information, see the DIY Lightspeed Passive Attenuator.

What's Playing: Marta Gomez - Canta

Simple DIY Monitor Speakers

2009-04-13T21:24:00.009-05:00

We recently received an email asking for some clarification about the difference between line-level and speaker-level Baffle Step Correction Circuits with a reference to the DIY S.E.Xy Speaker Project over at Bottlehead.com. This message brought our attention to a very simple speaker project that we thought we would point out to our readers. A photograph of the S.E.Xy Speaker Project is shown below.

In short, the small sealed monitor speakers are comprised of inexpensive Fostex FE166E fullrange drivers and housed in prefabricated Dayton Audio 0.25 ft^3 cabinets from Parts Express. This is a very simple speaker project and the only woodworking required is a couple of holes through the front baffles for the drivers (electric drill and a hole saw should do).

What caught my attention with this project was the fact that the 6.5" Fostex drivers actually fit in the small prefabricated speaker cabinets. While I have used the great looking Dayton Audio speaker cabinets in the past, I never bothered to check if the 6.5" Fostex drivers would fit.

Fostex FE166E vs FE167E
Of course some of you may prefer to use the Fostex FE167E fullrange speaker driver in place of the FE166E and that should not pose any issues. The FE167E has the same efficiency of 94dB but with it's higher Qts it will be able to produce more bottom-end which will allow you to lower the crossover point and possibly even allow you to get away with just one subwoofer. The figure below shows the modelled frequency response of the two drivers in a 0.25 ft^3 sealed enclosure.

The modelled response shown above uses the T/S Parameters noted on the Fostex data sheets. However, based on our experience with measured T/S Parameters from other Fostex drivers, expect Qts to be a little larger than noted on the data sheet. This means that we can expect a little more bass than what is shown on the plot. In addition to getting more bass out of the FE167E, you may also prefer it as it does not exhibit the rising frequency response of the FE166E which some may find too shouty.

Baffle Step Compensation: Line-level vs Speaker-level
This speaker project was meant for use with the 2W Bottlehead Single Ended eXperimenter's amplifier and therefore Line-level Baffle Step Compensation is the most practical choice as it won't waste the precious power of small tube amps. If power is not a concern, you can use the Baffle Step Circuit Calculator to come up with suitable speaker-level circuit.

For those wondering about the line-level BSC I have run a couple of simulations. I did not know the input impedance of the Single Ended eXperimenter's tube amp so I assumed 100k-ohms.

It would be a good idea to try the BSC on a protoboard and adjust the values to suit your room and personal taste. I would start without the 1.2nF (0.0012uF) capacitor, especially with the FE166E.

The inexpensive Fostex drivers work well in sealed enclosures. I am still very happy with my Sealed Fostex FE127E Bipole Speakers. For those of you afraid of woodworking, the prefabricated Dayton Audio cabinets are for you. Also, for the time being PartsExpress is offering free shipping on most orders over $98 (limited to USA).

More DIY Bookshelf Speaker Projects:

What's Playing: Emilie Mover - That Song

Giveaway #2 - MyRefC LM3886 Chipamp Kit

2009-03-25T22:38:00.004-05:00

Back in January we had Giveaway #1 and gave away a copy Building Valve Amplifiers by Morgan Jones to Bill in Georgia. Well, with Spring just around the corner we are in a good mood and are having another giveaway. Once again the giveaway will be held on the DIY Audio Projects Forum and you will need to be registered on the forum in order to enter for the giveaway.

The giveaway is for two mono kits (which will make one stereo pair) of the MyRefC LM3886 chipamp. The kits were recently put together by Uriah and Peter as part of a large groupbuy. The groupbuy was a very large effort so thank you very much guys (I got a kit for myself that I will build shortly). Also included in the giveaway are two 160VA (120V primary, dual 24V secondaries) transformers for use with the amplifier modules. This will allow you to build two mono-block amplifiers if you like. To finish off the amplifier kits, you will need to supply your own audio and power hookups (RCA, Speakers, IEC, power switch, wire ...) as well as a suitable heat sink and chassis (or two). A photo of the kit contents is shown below.

The chipamp design is by Mauro Penasa and it has been well received. A schematic of the amplifier is shown below.

In order to enter for the giveaway, you need to post a message in the Giveaway #2 - MyRefC LM3886 Chipamp Kit thread with one or more photos attached and a brief description of the photos. Complete details and giveaway rules are provided in the message thread. The giveaway ends April 10, 2009 at 18:00 (CST) (UTC-6) and the winner will be chosen at random.

Good luck.

What's Playing: Feist - Secret Heart (180g LP)

Return of S-5 Electronics K-12 Tube Amp Kits

2009-02-18T19:28:00.006-06:00

The most common questions we get from our website visitors are about the inexpensive and simple K-12 Tube Amplifier Kits by S-5 Electronics. These little tube amp kits have generated a lot of interest over the past few years, but for a little over a year now the question has been ... "The K-12 tube amplifier kit is no longer available - can you suggest a comparable kit?" Back in December 2007, Bruce tried out the new S-5 Electronics K-8LS Tube Amplifier Kit to see if it would make a suitable replacement for the K-12. Unfortunately the performance of the K-8LS was poor. So for over a year, we have not been able to suggest a simple to build and inexpensive tube amplifier available as a kit.

A couple of days back, Lofton posted a message on the DIY Audio Projects Forum letting us know that the S-5 Electronics K-12G Tube Amp Kits are once again available (Thanks Lofton). Well, this is great news and now we have an answer to a very common question that we get.

The photo below shows the contents of the recent K-12G Tube Amplifier Kit.

The contents are very similar to the previous kits which came with the 10GV8 tubes. One thing that I did note is that the power transformer appears to be larger than the one which came with my K-12M Tube Amp Kit. This should be an improvement as my K-12M power transformer runs hot, but in fairness, has not failed even after several years of use. The K-12G kits are modestly priced at $189.95 and available from Tube Depot. Right now (Feb 2009) Tube Depot is offering a free 3.5mm to dual RCA cable that you can use to connect the tube amp to your portable music player. It's not clear if this is a limited time offer.

Please note that these kits do not come with an enclosure. Instead they come with a pine board which will allow you to mount all of the parts and put together a fully functional amplifier. However, this will not be practical and possibly unsafe for most environments. There is high voltage present on the board and the tubes get very hot, so you don't want little fingers or paws poking around the amplifier. So be prepared to construct or buy a suitable enclosure for the kit.

Update March 2009: Here is a finished photo of Lofton's K-12G Tube Amplifier Kit.

If you do pick up one of these simple and fun tube amp kits, here are a few links that will give you some enclosure and modification ideas.

S-5 Electronics Tube Amplifier Kit Resources:

S-5 Electronics Tube Amp Kit Photo Gallery
Bruce's Modified K-12M Tube Amp Kit
Mark's K-12M Tube Amplifier Kits

If you do build one of these kits, please send us photos so we can share them with our readers.

What's Playing: Steely Dan - Aja (LP)

Jean Hiraga's Super Class-A Amplifier

2009-02-08T20:59:00.007-06:00

Dan has completed a follow-up project to the Jean Hiraga - "Le Monstre" 8W Class-A Amplifier that he built back in July 2008. Impressed with the result of the 8W Hiraga, Dan set his sights to another Jean Hiraga design - the bigger "Super Class-A 30W" which also had previously appeared in the French magazine "L'Audiophile".

The original driver transistors were used, but seeing that the original power transistors are no longer available, Dan opted for Toshiba 2SA1943 and 2SC5200 transistors. The new transistors allowed the use of a higher rail voltages (35V vs 24V), resulting in a measured power output of 58W of Class-A power.

The amplifier enclosure was constructed using aluminum channels and plates. As one would expect with a Class-A amplifier delivering this much power, the heat sinks are huge and so is the power supply (500VA transformer and 1.2 Farads of filter capacitors.

Dan reports good sonic results from this amplifier. "Jean Hiraga's deceptively simple and pure circuit topology once again shines through. The sound seems effortless and gives the impression of a much higher power amplifier yet still being able to produce all the low level details, the sound which Class-A is renowned for."

For full details of Dan's project, see the Jean Hiraga's Super Class-A Amplifier project page.

Additional DIY Solid State Audio Projects:

What's Playing: Sarah McLachlan - Adia

Seas Drivers and Granite Loudspeaker Box

2009-01-08T21:40:00.005-06:00

I've seen some pretty sharp looking diy speaker projects on the net, but these guys take the cake.

The enclosure for these great looking and unique speakers is made out of 20 mm thick black granite. Yup, granite. Once finished, each loudspeaker checks in at about 35 kg so you don't want to drop these. The speakers were put together by Radoslav and his friends in Slovakia. The speaker enclosure is a 15L bass reflex design that is tuned to 45 Hz through a rear firing port. The drivers were sourced from Seas and consist of a G17REX/P woofer and 27 TFFC tweeter. The dividing network is second order at 2500 Hz.

The measured frequency response is very flat and shows surprising low end response despite that enclosure size is relatively small size. Radoslav reports that the finished speakers sound and look great.

See the DIY Granite Speaker project page for full details. Obviously there are very few of you that will have the resources to replicate this project, but it is nice to look at and there is no reason why it should work well using more practical enclosure material like wood.

What's Playing: Diana Krall - 'S Wonderful

diyAudioProjects.com Giveaway #1

2009-01-04T10:54:00.003-06:00

We are a few days late, but Happy New Year and all the best in 2009.

To kick in the new year, we are having a Giveaway on the DIY Audio Projects Forum. The giveaway will be for a the book Building Valve Amplifiers by Morgan Jones.

To enter for the giveaway you will need to registered on the DIY Audio Projects Forum. Yes you will need to enter your email address and no we won't be giving it away or sharing it with anyone.

To officially enter you need to upload one or more photos attached and a brief description of the photos in the diyAudioProjects.com Giveaway #1 thread. Details and giveaway rules are provided in the message thread. The giveaway ends January 15, 2009 at 18:00 (CST) (UTC-6).

Good luck.

What's Playing: Joe Jackson - Go For It

Moving Magnet Phono Preamp Kit

2008-11-30T23:45:00.006-06:00

Mark in Australia has put together a moving magnet phono preamplifier using a electronics hobby kit. The phono preamp kit provides everything you need except minus an enclosure and a power supply (AC walwart). The circuitry is contained on a printed circuit board (PCB) and consists of operational amplifiers (opamps) with up to three equalization compensation circuits which can be selected with jumpers or a switch. The kit comes with LM833, but you can use which ever opamp you prefer. The power supply is also on the PCB and uses 7812 / 7912 regulators. The design supports all of the common compensations and several 78 compensations as well.

The enclosure and power source need to be provided. For the power supply Mark used a walwart (15VAC) and the circuitry is contained in a plastic (ABS) enclosure. The inputs/output were moved to the rear.

Mark reports that the kit is dead quiet, performs well and can hold it's own against the popular Pro-Ject Phono Box SE preamp. See the project page: DIY MM Phono Preamplifier Kit (Moving Magnet) for full details.

Other Phono and Turntable Information:

Lundahl Moving Magnet Phono Step-Up Transformers

What's Playing: Cocteau Twins - Pandora

Simple Low Resistance Measurement

2008-11-26T20:02:00.008-06:00

This is a question that we get often:

I measured the direct current resistance (DCR) of xyz using a multimeter and the result is higher than what the data sheet says it should be!

Since most of our readers are audio enthusiasts, xyz is typically a speaker, but it could be any low resistance device such as a resistor, switch or relay contacts. When trying to make a resistance measurement of low resistance devices using a common multimeter, the results are often high and almost meaningless. The reason for this is that the test currents generated by most common multimeters are very low, typically much less than 1 milliamperes (mA).

A simple way to measure low resistance is to use a "4-wire resistance measurement method". Ohm's Law states that V=IR. Resistance (R) is what we are interested in determining. Since we already have multimeter that is pretty accurate at measuring voltage (V), all we need to do is fix the current (I) and we can calculate the unknown resistance.

Figure 1 (click to enlarge) shows a schematic for a very simple low resistance measurement jig. Basically it is a LM317 voltage regulator that is set to deliver 100 mA of test current.

Figure 1 - Low Resistance Measurement Circuit

In the circuit, a fixed 12 ohm resistor is used to set the current of the regulator to about 100 mA (a 12 ohm resistor actually sets it at 104 mA, use the voltage regulator calculator to check).

Building the Low Resistance Measurement Jig
The test jig is very simple to build. The photos below show the measurement jig that I built. The LM317 was recycled, a 12 ohm resistor, a couple of alligator clips, a project box (Radio Shack 270-1802) and an old 5V 300 mA cell phone charger. For the power source something in the order of 4 to 6 V capable of more than 100 mA will work fine. Batteries can also be used - as little as three AA batteries will work. Note that a 9V battery will not work as it cannot deliver enough current.

Photo 1 (above) – Low Resistance Jig Parts (click to enlarge)

Photo 2 (above) – LM317 and Set Resistor (click to enlarge)

Once you have built the jig, it is a good idea to check the test current to make sure it works. Mine produces a constant current of 105 mA. Anything between 95 and 105 mA will be fine as we will see later.

Photo 3 – Finished Low Resistance Jig (click to enlarge)

Using the Low Resistance Measurement Jig
Using the jig is very simple. Set your multimeter to read voltage. The lower you can set the voltage scale, the more accurate your readings will be. To determine the unknown resistance, simply connect the constant current across the device you want to measure. Now measure the voltage across the device you want to measure. Once you have measured a voltage you can apply Ohm's Law to determine the unknown resistance.

A 100 mA current was chosen for a reason - to make the math easy. With a 100 mA test current you can multiply the measured voltage by 10 to determine the unknown resistance. If you need very accurate low resistance measurements you can use the exact test current of your jig and an Ohm's Law Calculator to determine resistance.

Here are a few examples using the DIY low resistance test jig and a Wavetek Meterman multimeter:

0.1 ohm resistor measured 0.0112V (11.2mV), multiply by 10 and you get 0.112 ohms. In contrast, using the multimeter set to the lowest scale (200 ohm) 0.4 ohms was measured.

0.22 ohm resistor measured 0.0217V (21.7mV), multiply by 10 and you get 0.217 ohms. In contrast, using the multimeter set to the lowest scale (200 ohm) 0.5 ohms was measured.

0.47 ohm resistor measured 0.0481V (48.1mV), multiply by 10 and you get 0.481 ohms. In contrast, using the multimeter set to the lowest scale (200 ohm) 0.8 ohms was measured.

As you can see, for small resistance a common multimeter is very inaccurate. Of course you can spend a lot of money on a meter that can measure low resistance, but where is the fun in that? One should be able to put this jig together for less than $10.

DIY 12AU7 Tube Preamplifier

2008-11-24T20:18:00.006-06:00

This is Alan's mini-tube preamplifier.

It is a very simple tube preamplifier project that will work with the 12AX7 or 12AU7 vacuum tubes, both of which are fairly common. The preamp is built using primarily parts that Alan had on hand. To make a real frugal build, the preamp can be built using 12V transformers and placed back-to-back in order to get the required high voltage and for the heater supply. Total costs for this project ran Alan about $30, with the majority of those costs going towards the enclosures and RCA jacks.

The power supply is housed in a separate enclosure, also from Hammond. For full information, see the project page: DIY 12AU7 / 12AU7 Tube Preamplifier.

Related Tube Preamplifier Projects:

What's Playing: Ingrid Michaelson - The Way I Am

6T9 Compactron Push-Pull Tube Amp

2008-11-08T11:19:00.005-06:00

Steve has sent us details on his latest vacuum tube amplifier project.

Steve tells us that this great looking vacuum tube amplifier project was inspired by the Spare Time Gizmo single-ended 6T9 tube amp kit from 2004. The circuit ideas for the push-pull output stage came from his EICO HF-81 and RCA Receiving Tube Manual. The preamp stage uses 12AX7A tubes.

All of the connections are point-to-point. For the enclosure, the combination wood and brass chassis consists of a small sheet of brass and Poplar wood. The brass sheet was polished to a shine and the Poplar wood stained with Minwax Red Mahogany stain and finished with an Amber Shellac.

Steve is very impressed with the performance of this tube amp. He notes that there is plenty of gain and a nice rich sound.

For full information about this project, see the 6T9 Push-Pull Amplifier Project page.

Great work Steve!

Related 6T9 Compactron Tube Amplifiers:

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KT88 Push-Pull Mono Block Tube Amps

2008-10-29T20:48:00.007-05:00

Bruce from the USA has completed his second follow up to his original OddWatt tube amplifier project (a EL84/6BQ5 Push-Pull Tube Amplifier) with the Odd Blocks. The Odd Blocks are a pair of KT88 Push-Pull Mono Block Tube Amplifiers. Like the Oddwatt 225 (a KT77 SIPP (Push-Pull) Tube Amplifier), the Odd Blocks are also scalable and will work with a number of octal tubes such as KT77, EL34, 6CA7, 6L6GC, KT88, 6550 and KT90. A photograph of the finished mono block tube amplifiers is shown below.

Like the previous OddWatt tube amp projects, the topology of the driver stage is an SRPP this time using 12SL7 tubes. This feeds a self-inverting push-pull (SIPP) output stage operating in Class A Ultra-Linear (UL) mode. The output tubes are Gold Lion KT88. LM317HV regulators are used to form the constant current source (CCS) on the output tubes. An underside view of the amplifier is shown below.

Like the precursors to this project, the KT88 provides very good performance. The SRPP and SIPP output stage combine to produce a very low noise floor. The design can be scaled for use with other tubes by simply adjusting B+ voltage and cathode current.

For complete information about this project, see the Odd Blocks project page - KT88 Push-Pull Mono Block Tube Amplifiers.

Related DIY Tube Amplifier Projects:

Alex's KT88 Single-Ended Tube Amplifier

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Fostex FE167E Bass Reflex Speakers

2008-10-19T16:45:00.012-05:00

by Mark Houston

The very first pair of speakers I put together some thirty-eight years ago was a pair of single-driver loudspeakers using 8” Kaltro twin cone drivers. As I type this, I find myself once again listening to speakers using a single full-range driver. This time it is the 6.5” Fostex FE167E fullrange driver. I had recently completed a small low wattage 6T9 valve amplifier, and asked Gio for some suggestions on speakers to match the amp. He suggested the Fostex FE167E. When I saw they were 94dB efficient I ordered them instantly. Packaged with the drivers were two enclosure plans - a floor-standing unit as well as a bookshelf enclosure. I opted for the smaller bookshelf speaker box. The Fostex Recommended Standard Bass Reflex Type Enclosure is 15L with a 50 by 50 mm port that can exit from the front or rear. The enclosure plan is shown below.

The speaker boxes were put together by a neighbor using 18 mm MDF. The boxes were clamped during the gluing process and the inside joints were sealed with additional glue. The back panel had heavy speaker sound absorbing vinyl glued over its surface and the box was lined with a single layer of thick Dacron (tontine).

The binding post block was fitted and oxygen free copper speaker wire was used for the connections. Sealing sticky back foam was placed under the connecting block and also under the drivers which were screwed in place. The boxes were pre-sprayed with paint. Later grills were added by cutting the center out of a piece of MDF, stretching and stapling speaker cloth over the frames. The grills were attached to the speakers using Velcro.

The baffle step correction / compensation (BSC) calculator can be used to determine a BSC specific to the width of your baffle. The amount of attenuation required will be subject to your listening room and amplifier as well as personal taste. Typically about 4 to 6 dB of attenuation is good. You can experiment with the component values shown below and select a BSC to suit your room, amplifier and personal preference. I am using L=1mH and R=2.7ohms.

Out of the box the first thing you notice about the speaker drivers are the ultra-light the cones and very stiff suspension. The first few days of playing will see the drivers settle though expect to put in twenty to fifty hours before they settle completely. If you are not use to listening to single-driver loudspeakers you may be a little shocked at first. I was, but it doesn’t take long to recognize the all the good qualities of a single-driver speaker system. At a recent Melbourne Audio Club night held at my residence the Fostex FE167E speakers were auditioned with a small 6T9 tube amplifier and they received many accolades from the very discerning listeners. When compared with small 2-way bookshelf speakers the Fostex FE167E produced more bass and equal treble response. Most members could not choose one pair of speakers over the other. Voices however do appear forward on strong vocal tracks. This is not unpleasant just obvious.

When teamed with the 6T9 tube amp, for which they were intended, they really come into their own. They are LOUD with only a few watts driving them, produce good bass and excellent mids and highs. The Fostex recommended enclosure design works well with the drivers and produces some excellent violin and cello gritty earthy notes in the instrument's resonance and character. Piano sounds soft, rounded and musical. Voices tend to come forward a little of the rest of the instruments as do some upper-middle frequencies. This adds some extra dimension to your listening.

Update: 4 May 2009
The plot below shows the measured near field response of the speaker system. The upper line on the plot is the measured response with no filters in place. The lower green line is the response with a baffle step compensation circuit of about 3dB.

See the Fostex FE167E Fullrange Driver page for more information and enclosure ideas for this driver.

More DIY Bookshelf Speaker Projects:

DIY Jordan JX92S Tower Speaker

2008-10-13T15:08:00.001-05:00

Gary from the United States has put together a fantastic looking pair of tower loudspeakers. His speaker project uses the Jordan JX92S Fullrange Driver which I have used myself and is a fantastic fullrange driver.

The fullrange JX92S speaker is housed in a vented enclosure with a volume of about 1.3 cubic feet and a box tuning of about 35 Hz. As you can see, Gary has done a great job with the finish on the DIY speaker cabinets. The enclosure is constructed using Baltic birch plywood and finished with maple and walnut veneer and a tung oil stain.

Gary reports that the Jordan JX92S drivers can deliver a lot of bass which is uncommon for fullrange drivers of this size class. He also indicates that the speakers sound great, open, tight, fast and as expected, image like crazy. The nice thing about these drivers is that they can also handle all types of music without any signs of strain.

For additional information, pictures and enclosure design, see the Jordan JX92S Tower Loudspeaker Page.

Additional Jordan JX92S DIY Loudspeaker Projects:

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Isobaric 6th Order Bandpass Subwoofer

2008-10-12T11:24:00.006-05:00

Dan McGrath (from Great Britain) sent an email with a link to his recent DIY Subwoofer project. For the subwoofer project, Dan decided to use an Isobaric Sixth Order Series-Tuned Bandpass enclosure. The basic layout of a 6th order isobaric bandpass enclosure is shown in the figure below.

The enclosure was constructed using Medium-Density Fiberboard (MDF) which is inexpensive and easy to work with. To make the enclosure rigid, Dan doubled up the MDF as shown below (click photo to enlarge).

For the subwoofer project Dan used two Eminence Beta 10 drivers. The Eminence Beta 10 is an 8 ohm, 10 inch bass driver with a power rating of 250W and a sensitivity 97 dB. With the very high efficiency of these drivers, the subwoofer will be able to produce high SPL with only modest power. The Eminence Beta 10 is readily available (often locally) and it is relatively inexpensive. The photo below (click to enlarge) shows the two drivers in the baffle.

The finished subwoofer enclosure is shown in the photo below (click to enlarge). Dan has been using the subwoofer for a few months now and is very pleased with the results. That should not come as a surprise considering the level of effort he put in to this build. Very nice work Dan.

Dan has compiled a very detailed build log of his subwoofer project on his website and there are plenty of photographs. Take a look at his page for more information on this project.

More DIY Subwoofer Projects:

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Swans Tempus Bookshelf Speakers

2008-09-25T21:04:00.007-05:00

Daniel Bolduc (from Canada) sent us an email informing us that he has finished a another set of DIY Speakers. His latest project is two sets of Swans Tempus Bookshelf Speakers by HiVi Research. The Tempus speakers were featured in the German sound magazine KLANG+TON in their June 2002 issue which commended the excellent acoustic response of this bookshelf speaker.

HiVi Research offers the Swans Tempus speakers as a kit, but in true do-it-yourself (DIY) fashion, Daniel sourced the parts himself and built the bookshelf enclosure. The Swans Tempus bookshelf speaker uses the HiVi Research F6 Mid-woofer which features a Kevlar/paper curvilinear cone, phasing plug, and alloy basket. The tweeter is the HiVi Research TN28 which is a silk dome tweeter in an open-air housing. The photo below shows Daniel's finished speakers.

Technical information, enclosure dimensions and measurements of the Swans Tempus Bookshelf Speakers is available from the manufactures website. The bookshelf speaker enclosure plan and crossover are shown below (click to enlarge).

For the speaker enclosure Daniel used 1" thick laminated maple. The finish on the cabinets is four coats of transparent spray lacquer. The photo below shows a rear view of the finished bookshelf speakers (click to enlarge the photograph).

Daniel had the following comments about the Swans Tempus Bookshelf Speakers

"After about 80 hours working on the project, the Tempus speakers are finally done and I can assure you that they are sounding great. Bass frequencies are deep and clean while the highs are well balanced. But, due to either the limitation of the TN28 to 20 kHz or the crossover network, high frequencies are not as well defined and crisp as on the 1.618 speakers I built few months ago."

"Even with this little lack of highs, I'm very satisfied of the sounding of these speakers and the pair that is hooked on my computer performs much better than all computer speakers systems I've ever heard (I didn't hear a lot of systems but you have to start somewhere!)."

The 1.618 speakers that Daniel is comparing the Swans Tempus speakers are a DIY speaker design by Adam McCall - 1.618 - 3-Way Hi-Vi Tower Speaker Project.

Daniel has put together a detailed build log of the Swans Tempus speakers on his site with plenty of photographs.

More DIY Bookshelf Speaker Projects:

What's Playing: Dire Straits -Sultans of Swing

DIY Jordan JX92S Open Baffle Speaker

2008-09-22T11:33:00.005-05:00

Martin J. King of Quarter Wavelength Loudspeaker Design has added a new DIY open baffle loudspeaker project to his site. Martin's loudspeaker project uses a Jordan JX92S full range driver mounted on an open baffle in conjunction with a Goldwood GW-1858 woofer which is mounted in an H-frame. The picture below (click to enlarge) shows the new open baffle speaker design set up next to his Lowther DX3 ML-TL speakers.

As you can see, the enclosure is fairly simple and relatively compact (for open baffle speaker systems). The two-way dipole speaker systems covers most of the 20 Hz to 20 kHz frequency range. The H-frame configuration is used for the bass below 200 Hz and the small Jordan full range driver are for the frequency range from 200 Hz to 20 kHz.

As with all of Martin's loudspeaker projects, his latest is also very well documented and very informative. For full details about this loudspeaker project, see Martin's writeup: Jordan JX92S Open Baffle and Goldwood GW-1858 H Frame Two Way Speaker System - (PDF 1.68MB).

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Ultra-Linear 6T9 DIY Tube Amplifier

2008-09-04T16:47:00.004-05:00

It was always my intention to build two 6T9 vacuum tube amplifiers. For the first one I used a baking pan for the chassis and I was interested to hear just how good these simple single-ended (SE) tube amps could be with just basic components. From the first hour of play I was very impressed with just how musical they are when matched with the right speakers. My second build of this amplifier incorporated a lot of the original parts but this time more attention was paid to the construction and small upgrades to capacitors and the power supply. I also found that the sound could be further improved by converting the kit to operate from Pentode mode to Ultra-Linear (UL) mode. Both amplifiers are Class A.

The schematic below shows the tube amplifier circuit (click to enlarge). The items in red are the changes that are required for the conversion to UL mode.

To change the output section to UL the screen grid resistor (R107, 1k) was removed and the UL tap (tap 3) from the Edcor audio output transformer (OT) is wired directly to the screen grid (pin 10). Other changes I made to the amplifier circuit were to replace the input capacitor C101 (and C201) and the coupling capacitor C102 (and C202) with 0.22 uF metalized polypropylene types. This helps improve the bass response slightly.

The power supply schematic is shown below (click to enlarge). On the power supply I made the following changes which are shown in blue on the schematic. 0.01 uF polyester capacitors across the rectifier diodes. 0.1 uF polypropylene capacitors across all the electrolytic capacitors. One additional 100 uF electrolytic capacitor in the power supply.

Tube Amp Construction Notes
I wanted the amp to look cool (very black) and minimalist with its gold connections hidden and all hardware neatly tucked under a black enclosure. Two coats of Epoxy Enamel spray paint was used on the case once all drilling had been completed.

The amp is designed to deliver music well, to be unassuming in appearance and have a high wife acceptance factor (WAF). The OTs are slung under the top plate where the power transformer is mounted. Once again the power transformer and the OTs are rubber mounted. Multi-core shielded cable is used to connect the rear gold insulated RCA connectors to the 50k potentiometer and to the printed circuit board (PCB). The power switch was conveniently placed at the front of the amp and a captive power cord was used.

The potentiometer should be connected to the signal ground. Also keep the chassis earth and signal earth separate. Use the shielding on the input wiring to distribute the earth to the input RCA connections, potentiometer and PCB.

6T9 Tube Amp Measurements
The photographs below show the sine and square wave response of the amplifier. There is little to no change in the response compared to pentode operation.

Sine Wave Response - 1kHz @ 6.2V P-P, 8-ohm load

6T9 Tube Amp Sound
I played the new amp without NFB and with to determine the best sound. I found the amp sounded much better with NFB. The UL version of the 6T9 tube amplifier sounds better than the Pentode version. Because so many of the components are the same in both amps the improvement in sound is likely due to the UL operation mode.

Mark Houston

Additional 6T9 Tube Amplifier Links

DIY Home Theatre Speakers

2008-08-25T15:13:00.006-05:00

Back in September 2007 Adam constructed a pair of 3-Way DIY Tower Loudspeaker using all HiVi Research drivers. Well, as most of us in this hobby know - once you start building, you just can't stop! The photo below shows Adam's HT setup up in 2007 sporting his new DIY tower loudspeakers.

And here is a more recent photo of his HT setup.

In the photo are a couple of new projects. A DIY HiVi SP10 10" subwoofer and a DIY HiVi home theatre center channel. Consistent with his previous tower loudspeaker build, only drivers from HiVi Research were used and all of the speaker enclosures are constructed using MDF with a black oil based epoxy paint finish and red oak trim.

Adam reports excellent results and seamless integration with his HT setup. His only complaint is that he needs matching rear channels now. I am sure it will only be a matter of time before we see those. See the project pages for full information about these home theater loudspeakers:

What's Playing: A Flock of Seagulls - Telecommunication

Hybrid (12AU7 / IRF612) Headphone Amplifier

2008-08-05T22:01:00.008-05:00

Over the past few years, headphones have come long a long way. For $70 to $150 you can get a great sounding pair of headphones. Best of all, headphones allow you to get right into the music anywhere you are and you do not have to worry about annoying things like room modes and reflections. And for you do-it-yourself (DIY) audiophiles, there are also a number of great DIY headphone amplifier projects that you can choose from. Well, here is another one.

Rogers has put together a very simple hybrid headphone amplifier for use with 32 ohm Grado SR125 headphones. His hybrid head amp uses a vacuum tube voltage gain stage which feeds a MOSFET follower output stage. The tube is a the 12AU7 (ECC82) and the MOSFET is an inexpensive IRF612. The IRF612 is configured in a typical single-ended class A circuit using a passive constant current source (CCS).

What's best about this project is the power supply. Both the 12AU7 tube and IRF612 MOSFET are set up to operate at low voltage (~12-13V). Power for this project is supplied via an external switch mode power supply (SMPS). All of the project parts are readily available and one can easily put together one about $40. Rogers has reported very good results from this very simple project. For full project details, see the 12AU7 Tube / IRF612 MOSFET Hybrid Headphone Amplifier Project.

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