Monday, October 25, 2010

Brown Turds

I have used what has been euphemistically referred to as Brown Turd capacitors on the Hellfire board. I had to laugh when I saw then called that at a local website, Evatco. The pace is slowly picking up after the holiday. I didn't really plan for Nick to be peering at you through the wires it just turned out that way...

Tuesday, September 21, 2010

Hellfire Front Panel

Slowly getting there... Off on holiday in a couple of days so this won't get finished for a while... did stuff up the hole for the switch...
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Wednesday, September 8, 2010

Power Supply of Doom!

This is my dual 6V transformer. It was actually cheaper than one... Not really as neat but does the job. Got the LFO to arc up -- three more valves to go! Probably need the front panel to be in place for safety before we go too much further...

Friday, September 3, 2010

Thar she Glows!

Well got the rectifier going! It's a start anyway... only 4 more to sort out!

Sunday, August 29, 2010

Hellfire on PCB!

The PCB is moving foward at a bit more of a pace. Still need to fit all the passives and source the main transformer and sort out the front panel.
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Monday, August 23, 2010

Hellfire here we come!

My Valves arrived today! These are to go ito the Metasonix TS-21 Hellfire clone. The amazing, in more ways than one, Eric Barbour, has very kindly let Cat Girl Synthesizers put up the schematics of a few of his TS era designs. I have done most of the PCB and have one of the transformers but there is still a fair way to go...

Sunday, August 8, 2010


This is the Temco attached to the X-4046 VCO...
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Friday, August 6, 2010


I have never really got into getting the 1V/Octave tuning exact before and so I have decided to get a bit more serious about it all! This is the first experimental cut with the MIDI board (on the left) driving the X-4046 VCO (on the right). I then have a Ruby script that steps the MIDI interface and then queries the Digital Frequency Counter for the current frequency. I then do some maths and work out the slope for what would be a 1V/Oct and tweek to suit. A sweep takes about 3 or 4 minutes so the turn around is pretty good. I have also done an overnight run without a Tempco and plan to do another with to see the difference!
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Friday, July 23, 2010

X-4046 VCO

Hmmm another VCO as well! Have tweeked in a couple of other oddities...

Wednesday, July 21, 2010

Mutant VCF

This is the almost stuffed Serge Mutant VCF -- it is an attempt to be a Serge VCF with voltage controlled Frequency, Resonance & Slope. Not really sure that having all three parameters Voltage tweekable will work but it is easy enough to drop back to just two, as in the originals... I have used That Coporation quad transistors for the gain cells in a hope that it will be both quieter and more stable than the original. I have also used silver mica capacitors in the analog path. Looks like and intersting filter, from reading a few reviews on the net. It's not like I really need another filter...

Thursday, July 15, 2010

XFade Vactrol

Not the typical Buchla Vactrol but still seems to work OK...


Part of the Buchla Music Easel wavefolder clone. This is a VCA/Mixer that originally mixed between two wave shapes in the VCO. Here it has been just used as a VCA for a sinewave. The sawtooth used to modulate the signal gives a bit of an idea about the response but there is an enormous lag in the response time.
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Tuesday, July 6, 2010

That's Spoilt it's Looks...

Found the problem with the Sync Circuit... the Transistor Array got some of it's pins changed along the way and whilst they are correct there is a special pin that is tied to the substrate... This is supposed to be at the lowest potential of all the transistors on the device... in theory... So we end up with this to get around some of those problems! We do now get s signal through to the output of the OTA and the transistor beyond... seems to get a bit lost after that though....
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Monday, July 5, 2010

VCO Basket weaving...

The Sync circuitry on this thing has got knobs on it...

Monday, June 28, 2010

Sinewave Fun...

Well slowly more and more of the 921B VCO comes to life. I am having fun with the Sinewave shaper today and getting a reasonable shape coming out but there are still quite a lot of harmonics... It seems like the amplitiude of the Triangle wave is just too low to get a good Sinewave. The non-linearities of a transistor curve are exploited to get the shape and there is an input amplitude adjustment but I have it hard at maximum to get the best output. The other two adjustments in the circuit balance the two sides of the sinewave and both mimize the harmonics within their travel... I am also getting a fair amount of high frequency "hash" on the waveform from a lack of decoupling capacitors! Will try and clean that up tomorrow then on to the really intersting part -- the Sync section... Not like any sync circuit in any other music synth that I have seen before! As I progress through this I am really tempted to make a clone of this which is more 21st century, use better matched pairs and slightly less obscure parts and newer multipler etc. I suppose then it isn't really a clone... Other intersting things are the output levels. Most modern VCO's are adjusted for 10V peak-to-peak on everything where as this is a lot lower and adjusted for more of an equal audible loudness. By that I mean that the sinewave is 1.8V p-p, the triangle is 1.4Vand the pulse 2.2V -- not sure if anybody else does that? Also seems odd that the pulse is so much more...
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Monday, June 21, 2010

It Lives!

Really thought that I must get back onto the Moog 921B VCO. I was having a LOT of trouble getting a dual JFET... any dual JFET not necessarily the right one. Getting a through hole one from Mouser came in at a staggering $118 US! I then found a surface mount part that is similar in nature and managed to completely stuff up the footprint... I then did a fair bit of simulation with LTSpice and discovered that the offending section of the circuit is little more than a very high impedance buffer. Since this thing was designed long before FET input op-amps this was effectively what it was trying to achieve. I ended up removing a bunch of diodes and resistors and swapped the OTA for a CA3140 and added two jumpers --Hazaar! the result a sawtooth! I will tidy up the layout a bit so that it can be done either which way but I seriously doubt that it is going to make much sonic difference....

Tuesday, June 15, 2010

ARP Odessey VCO

Not really sure why I need another VCO... but anyway we have one now! Well actually two! The FET's were all from what was hanging around but still seem to work. I didn't get too caught up in matching the transistors as I probably need a VCO for other stuff...

Thursday, May 27, 2010

Wave Folded!

Well it works! The top trace is the sinewave in and the bottom is folded wave out!
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Wednesday, May 19, 2010

Upside Down...

This was the second PCB of the week. It is a waveshaper that has been lifted out of part of the Buchla Music Easel. The original PCB and stuff was done by Aaron Lanterman. There were a few issues with his original cut of the board but he does have quite an entertaining Video which is on YouTube. TekniK on the electro-music forum has done a layout that has repaied the errors and made it single sided. It is a pretty good job as there are a lot of bits on a pretty small board and only a moderate number of links. You can read about it here. You will probably notice that I managed to get the board etched upside down... again... Hence the OpAmps are hiding on the copper side! I have done some simulation with LTSpice and it is fairly typical Don Buchla with some fairly unusual design elements! Still got a bit of a way to go and I suspect that there are still some tweaks to get this going as per required...
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Tuesday, May 18, 2010

New Noise!

Have had another crack at the Tom Henry Noise source from the 21st Century Synth. Really pleased with how this PCB came out... Did another PCB this evening from the eleco-music forum with slightly less success... Oh Well!
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Wednesday, April 28, 2010


Revisiting the CGS65 -- it has never really worked properly...
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Thursday, April 22, 2010

Resonant Filter Module

Part of the Elektor Resonant Filter Module... Got the wrong Pot's... So close to actually going and now it will be another week or so!
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Tuesday, April 20, 2010

Not Teenagers Anymore...

Looking to build a complete metal can VCO in the not to distant future!
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Monday, April 12, 2010

DSP coding

Started down the track of getting a VCO going. It has all sorts of strange modes that I have picked up from the Buchula 259 investigation that I started a while ago. Has some extra weirdness as well!

Tuesday, March 30, 2010

Moog 921B

Well here we go; my layout of a Moog 921B VCO is into the stuffing phase... There are rather a lot of wire links... there are also a LOT of trim pots on the board... what was Bob thinking? I think that a lot of them are really there to adjust the controls on the front panel so they agree with the readings on the knobs...
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Monday, March 8, 2010

Eye Candy

Have this new (ancient) display for Forbin... it came from a B53 bomber via Texas...
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Tuesday, February 9, 2010

Through the Zero Plane

Some excitement when I got the En129 (ElectroNotes TZVCO) to work. I had a few problems etching the board (see previous posts) and then I had a few problems getting it to work. I then found a few missing resistors from the schematic when I had copied it into the PCB program. Anyway now all is good except for a couple of resistors mounted on the bottom!

Here is the board:
The layout is reasonably tight but there are a few more links that I would have liked. I probably could have juggled around the opamps between the packages to get rid of a few but I was getting a bit fed up with it all by that stage...

This is the result of some very simplistic testing. Looks a bit like some of the photographs that I have seen for the scope outputs from the Teezer and the ZeroOscillator.

Might ask Bernie Hutchins if I can post the layout for press'n'peel to electro-music or somewhere...

Wednesday, February 3, 2010

On the List "To Do"

I probably need to stop generating Boards and get them attached to some front panels! This is what is waiting for a panel & some knobs. There are about 50 boards here -- some of them will probably go into the prototyping/experimental pile but most seem to be running OK!
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Thursday, January 28, 2010

More Noise...

Well arced up the Frequency Counter and the Spectrum Analyser and had a bit of a play. The Linearity of Oscillator is pretty good as you can see that over a 10V range it is very close to a straight line -- especially for a couple of transistors that weren't even matched! The lowest frequency response is pretty close to pink and the other two show the increasing frequency response. You can see the lower level amplitude fall as the energy gets spread over a larger frequency range. The picket fence effect is, I think, due to the output being a square wave -- it is well outside the hearing range of most people anyway...

Random Success

Had some success with this board. I layed out a PCB for one of the modules in Thomas Henry's A Synthesizer for the 21st Century. This is the the Voltage Controlled Noise Source. I may put up the PCB layout but it isn't the most compact. It also didn't come out quite as well as I had hoped as the ground plane pour was too tight on the tracks. Anyway about half an hour with the Oscilliscope and a bit of head scratching tracked down the shorts and it is all working well now even if it isn't the most attractive of boards! I think that maybe turning the CMOS devices through 90 degrees might make a more compact board... I have already changed this layout to make the log converter a bit more accurate with some spare LM394's I have got so I may persist... Will try and post some pictures from the Spectrum Analyser tomorrow for some academic interest...
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