Saturday, September 14, 2013

Digital Frequency Counter 1960's Style

This is another project that is progressing agonizingly slowly... It is based upon a VERY old Digital Frequency Counter that was all old germanium transistors and small globes. I was going to try and to an authentic restoration but the globes had all corroded and kept falling off... There were also some sad things happening in the huge nest of transistors. I did find the schematic but really it was all a bit of a bridge-to-far. I have ended up making some small AVR boards and got some 5mm white LED's from Deal Extreme and it looks pretty original.

Sunday, August 25, 2013

Limping back into life...

Doesn't look all that exciting but the Hellfire Modulator is slowly limping back to life. The old sticky panel has been peeled off -- quite a task! and the holes re-drilled for two of the pots with switches and the larger hole for the PWM range switch made smaller -- quite a task II! and now we are getting back to being able to where we should have been 3 years ago...

Sunday, August 18, 2013

Asthetic has Knobs on....

This is a bit of an experiment in a number of ways. I have started on an 8 channel Envelope Generator that is based upon an enhanced DX7 style envelope control. I am also considering that really Forbin is going to be a bit big... I know that I am getting ancient and that large chicken head knobs are easy to see and that it all looks a bit Emerson circa 1974 but 40 years later I don't really have the space! Come what may the OctoEnvGen will be useful however it is packaged. It was a bit interesting to see though, how small a Euro synth actually is! I need to finds some knobs without markers on them though... These aren't pots but continuously rotating switches which control a TFT display which draws the waveform...

Thursday, August 15, 2013


Well a bit more daydreaming and have been experimenting with a few ideas. I have always been fascinated by the MOTM 520 Cloud Generator VCO. It is a bit of an expensive beastie having an original price of $500 and no DIY option. That has become a bit easier with a DIY option for the E340 being offered but still $270 + postage and the $US Vs $AU is not in my favor at the moment... Anyway the aesthetic behind Forbin is not to spend much money, just to be unique and learn a bit so this represents my experiment with similar ideas. I have no real idea how they do it internally but I have prototyped up 4 sine wave oscillators with separate Brownian noise sources that modulate the 4 oscillators. The Brownian rate of change (well frequency I suppose -- Chaos Bandwidth in E340 parlance) and amount that it is tweaking each of the oscillators (Spread on E340) seem to all work fine. I want to make the number of oscillators also continuously variable rather than just stepped. I also need to do some thinking about a soft clipping arrangement Vs a an amplitude compression technique. I plan to rework this in Assembler after some of the prototype parts in C have been bashed out. The nice thing about the CortexM4F is that there are truckloads of floating point registers -- actually 32! so it is possible to leave a lot of the parameters in the CPU rather than loading them in and out of memory all the time... The sample frequency of this thing should be around ~150kHz to 200kHz so hopefully not too many artifacts will get through. It is pretty impressive what you can get out of a $7.99 evaluation board + a simple DAC!

Tuesday, August 13, 2013

Wavolver ii+

Made a PCB for Ian Fritz's Wavolver II but have made the Pulse Mix and the Fold Mix voltage controlled as well. I am now contemplating an 8 channel Envelope Generator to allow me to control all these elements at once... Haven't quite got it all going yet but certainly en'route to success...

Tuesday, August 6, 2013

VS Voice

A bit more prodding and pummeling and for a bit of a laugh I loaded up a sample from the Sequential Circuits VS Synthesizer. This is allegedly waveform #20 from the wavetable. I have no idea if it is correct or not but there is an interesting interview with one of the chaps, Chris Mayer, that helped designed the VS and he mentioned that he wanted the interpolated sound of a short samples. Worked out that I can get all of the factory waveforms of the VS into one 48pin QFP... Thinking maybe a 7 segment display and a digital pot to choose the waveforms. Could do the joystick thing... could also do two control voltages for up/down and left/right. Might just start out with two waveform selections and a digital mix and see how we go from there...


Well into a little bit of DX VCO... The DAC works, the FPU works, the SPI works, some fairly basic code works and we end up with this! Did cheat a little and end up using a lookup table rather than a Taylor series. Since I really don't need the resolution and when you start scratching the surface the Taylor Series is a reasonable amount more mucking around than it appears and to try and run this as fast as possible I pinched some table generation stuff that I used for the LFO a while ago and re-jigged it a little bit. This is about 400Hz and the sample rate is up around 176kHz with a 16 bit resolution. Now need to get the ADC going...

Sunday, August 4, 2013

The spider...

Oh well... What could Possibly go wrong now?
Actually looks like it might work...

Friday, August 2, 2013


Hmmm... this is the 16 bit DAC that I bought... it is hiding in the shadow of the Evaluation board and as you can see from the 0.1" spacing of the standard DIL pitch are going to make this a challenging bit of work to wire it up... hopefully more successful than earlier in the week...

Thursday, August 1, 2013

Cortex M4

New project! yep another one... Looking at building a Digital VCO, there are a couple of options here; Texas Instruments, Atmel & STMicroelectronics. I am also getting a different TI part that has the the Cortex M4F core which has floating point! Pros & Cons? Well the Atmel board has 1Mbyte of external RAM, which will be really good for my wavetable VCO. The ST chip can boot along at 168MHz. The TI one I am probably the most familiar with... There are other options out there as well, the Frescale parts (was Motorola) have a more accurate ADC but it is still really only about 14 bits really (the trouble with having sensitive analog parts on a digital substrate), the NXP parts are also quite neat in that they can come with multiple cores so one core can be monitoring the ADC values whilst the main core can be doing the calculations... What I hope to end up with is a couple of different VCO's. The wavetable one that gets the samples from an SD Card. A DX Voice one that uses FM and looks like a single voice of my DX7 but the frequency is 1V/octave. A harmonic oscillator that looks a bit like a cross between a Farlight Page 5 and a Buchla 148 Harmonic Oscillator, well at least Mark Verbos's take on it here. I would also like to do another Buchla favorite, the 259, with the whole gamut of dual modulation of phase, frequency, amplitude and timbre... All I need is a little more time...

Wednesday, July 31, 2013

CPLD says No...

Been making a Divider circuit, it is sort of an enhanced MOTM 120/CGS UNI01/Polyfusion Divider. It all went a bit wrong though when the stupid printer made the transfer about 8% smaller... I rather rashly tried to keep going, with some persuasion I had got all the DIL parts in but it was a bridge too far to get the VQ44 package to work reliably. The JTAG programmer did see it but that was about as far as it was going to go... While doing it all I thought of a much easier way than using a CPLD anyway... so i will just jury rig that onto the board to see... the new idea also dispenses with quite a lot of other cruft on the board as well...

Sunday, July 28, 2013

Sockets + Knobs

Got a parcel from  Tayda and it arrived pretty quickly and the bits are certainly cheap. I now keep thinking of extra things I should have put on the order! Anyway hopefully this will make a few panels to sort of get things rattling along. Tried getting a few knobs and the chicken heads are pretty good -- a little smaller than the ones I have used in the past but quite nice. The Davis 1900 clones I am less enthusiastic about; I cannot get the grub screw to grip on the flat of a shaft OR the normal outside...
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Sunday, July 21, 2013

921B Mk II

Well having another hack at the Moog 921B. Here we have the Mk I looking on as the MkII gets drilled and it knows that all the expensive parts are about to be removed... The buggered up transistor array layout fix, like a beacon, knows that it's days are numbered... I am planning to make a complete Moog 15 in Euro and this is really the last bit that I need to make sure works properly as a true build before we embark upon that...

Thursday, July 18, 2013

Long Time Comming...

On a bit of a whim I built this VCO. I think I have the full house of Thomas Henry VCO's now! This is the last of XR, VCO1, 21C (or LM), X-4046 & the 555. Thomas has always been amazingly adept at getting various VCO devices to perform for a synth environment. This is the 8038 VCO that is from his VCO Cookbook. I bought the chip about 4 years ago but the book has only recently became available again. This is the layout from Fonik's web site but I only built one channel. It roared into life immediately but I think it will need more tweeking as the sinewave is a bit skewed...

Sunday, July 14, 2013

Climbing the Ladder

Put togther another variation on the Moog VCF ladder design. I had some spare LM394 matched transistors to use on ALL the pairs for this one... Haven't quite got around to firing this up yet but pretty close...
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Tuesday, July 2, 2013

Entwicklung Bau VCF

Taken a bit of a break from the Bergfotron VCO and whipped up a few boards last week. I know... what about the panels... This is quite an intersting VCF uses a different sort of OTA, the LT1228 from Linear Technology. It was designed by Stephan Winter for (I think) his final year project. The entire synthesizer is written up here. I was only really intersted in the VCF as it is quite different. The layout was quite pleasing as only one link! The tempco design is also quite intersting as it uses a realtively easy to get part and a couple of tricks to get it to 3300ppm/C. I don't usually bother with temperature compensating VCF's but I may try in this case just to so how well it works. The LT1228 seems to have really quite good specifications -- I did a bit of a comparison with the LM13700 today and I notice that quite a few parameters are missing from the LM13700 datasheet compared with the LT1228 which suggests that they probably aren't to special... The LT1228 is fairly expensive though... but not as much as a CA3280!
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Thursday, June 20, 2013

So where are all the panels?

Was going through the two large boxes that constitute the rather large number of boards that have been etched, stuffed and variously debugged and qualified to some extent then abandoned... This is YuSynth's ARP VCF that actually works really well! I plan to put in an order for more of the polycarbonate panels and the Cliff sockets and the chicken head knobs and make them a bit more useable rather than twisting the odd wire together... When I look at the gloat thread of muffs and the 2013 build pix on e-m i am amazed at the finished panel quality -- particularly the very black one that someone did recently -- so it really is time to get it looking good!
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Monday, June 17, 2013

According to Jung

Typical! After berating AbeBooks on a public forum it turned up... whoops... So that Karma is dished out the damn book doesn't have a description of the circuit that I bought it for!! It must be in one of his other books and since this book ended up costing me about $100 when you include the money shelled out for the first one that failed to show last year I don't really feel that inclined to go after the other ones. Having said that this book does have quite a lot of interesting articles -- particularly a section about Norton Amplifiers. Kind of wish that they would just put them on Lulu for $15-$20 bucks. I am now thinking that I might ask Bernie Hitchens as he mentions that they did an investigation into the Jung trick with modulating the power lines of the CA3080 in Electronotes En#63 -- had a bit of a look inside a LM13700 and seems like it should also work for that, but obviously effect both OTA's at the same time (which for Ian Fritz's Wood Wind waveshaper would be fine!)

Thursday, June 13, 2013

Stay on Target....

Well more work on the Bergfotron VCO but during lunch while day dreaming did experiment with a phase modulation option for a sawtooth oscillator... seems quite simple so not really sure why people haven't provided this before... probably sounds a sub-optimal?

Tuesday, June 11, 2013

Bergo Waves

Well the waveshapers are starting to work! Sawtooth, Sine, Square & Triangle all look good. The Double Frequency Sawtooth is a bit munted but I may have a wrong component in there... Have to check tomorrow. Was a bit surprised that all the waveforms are +ve rather than around ground when i realized that the voltage controlled wave selection won't work with a -ve signal... Got to drill a couple of missed holes with the dremel and with some luck should be able to try out the wood wind shaper tomorrow!
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Thursday, June 6, 2013

The Bergo Awakens!

I have been building the Bergfotron Advanced VCO for a very long time. I am pretty sure that I started this at least four years ago and it has lain dormant and unloved in the large box of Forbin possible modules. Recently I decided that it was a badge of honor to actually get this beast to life. Any self respecting Synth DIYer would rise to the challenge that Jörgen had thrown down. Well here we are -- we have the VCO core actually doing something. There has been a fair carnage in the component count that have visited this board and a lot of head scratching. There are a few wires that seem to be missing from the overlay drawing (the -1V to the CMOS switch) and a track missing (the -ve supply stops after the ferrite bead) but for sheer mid boggling options stuffed onto one board this is pretty much the pinnacle of design and you would have to take your hat of to Jörgen to have achieved that on a single sided board! Anyway I will keep trundling along as I want to get the wood-wind waveshapers to go! I have no idea how I am going to get all this onto a Forbin front panel but wait and see... hopefully not too long!

Thursday, May 30, 2013

Drilling ahead...

While eating my sandwiches at lunch time I drew up a PCB for a popular VCF. The only real difference is that it DOSEN'T use CA3280's as I am not paying 20 Euro + some exorbitant shipping for them... I have substituted some LM13700's instead as they are cheaper and less likely to be counterfeit...

Monday, May 27, 2013

The Pink wires!

Actually been a fair bit of activity recently and I have also been trying to plough through the dozens of semi-complete boards that are littering the house. This being probably the most challenging build of the whole lot. This is the VCO board from the Bergofotron and it is a complete beast! It has one particular aspect that I am really interested in experimenting with so after a lapse of 3 or 4 years since i started it the wires are going on...

Monday, February 18, 2013

LFO Noise Spectra

Well a bit of a break again but we are back into about 3 old projects. I have decided not to start anything new unitl at least 5 of the old modules get finished and panelized! This is from the Forbin LFO that I started ages ago that uses a dsPIC to generate the waveforms. Along with the usual suspects, Sine, Saw, Ramp, Triangle, Pulse I have put in noise and it will be brownian noise and the frequency control will also effect it. I have done a reasonable amount of work on it and at the momement is seems to work after a fashion. I seem to have a bit of a problem with the dc offset in the noise sources causing the integrated signal to run to a rail reasonably quickly. I am looking at ways of overcoming this at the moment. The rest of it seems quite good. This is the spectra of the white noise source that drives the brownian integrator. It is based upon some code from the internet. My other noise source is based upon a shift register approach but the spectra is even less flat than this one... I think that I will have to incorporate some sort of AC coupling of the signal in a digital sort of way... basically a high pass filter.
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