Scott Stites Synth DIY


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TriPhase/QFG, Sample and Hold,DSC2000

Rene Schmitz Tri Phase VCLFO/Thomas Henry Quadrature Function Generator

This is the Rene Schmitz Tri-Phase VCLFO/Thomas Henry Quadrature function generator module - my first completed module.

The PCB is stripboard and the front panel is a spare Schaeffer front panel kindly given to me by a friend, for whom I built the module. The PCB is mounted to the front panel with a home-made bracket fashioned out of flashing material. It is held to the front panel by the pots.

Since it was a spare panel, there are no markings at this time. The controls are: QFG Frequency, Tri-Phase Frequency, and Tri-Phase Frequency CV Intensity. There is one input, CV for the Tri-Phase frequency. There are seven outputs - Tri-Phase 0, 120 and 240 degrees and QFG 0, 90, 180 and 270 degrees.

Here is a picture of the module with a 'proper' Schaeffer front panel designed and mounted to the PCB by Jeff Pontius. He also had to change the size of the QFG frequency control pot in order for it to fit into his rack - I'd used the full size pots, and he replaced it with a pot with a smaller body. Those Schaeffer panels are really nice.....

Tri-Phase QFG with Schaeffer Panel

Below is a sample of the Tri-Phase in action. In this sample, the Tri-Phase is set to oscillate very slowly. Its output is controlling three devices - a Rene Schmitz VCO3, a Rene Schmitz VCO4069, and a Blacet Dark Star 2000. All are using pulse output.

The VCO4069 is not controlled by any other CV other than the Tri-Phase. The VCO3 is controlled additionally by the keyboard CV, using the Thomas Henry Digital keyboard's built in exponential portamento and additionally run through a Harry Bissell linear glide circuit. On top of that, another triangle LFO is mixed into the external CV input of the keyboard encoder to give a bit of vibrato to VCO3.

The Dark Star noise generator is set so that random pulses ocassionaly 'ping' its frequency, and also the noise output is pinging a Ken Stone Synthacon filter. Those are the ocassional low and high blips that are heard throughout the sample. The Dark Star output is internally providing pulse width modulation to its output.

All three VCO's are feeding the Ken Stone Synthacon VCF, which is slightly controlled by a Ray Wilson AR EG. The output of that filter is going into a Rene Schmitz MS-20 clone VCF. The MS-20 clone low pass cutoff is also controlled by the keyboard voltage.

After that, it goes to a Ray Wilson VCA, through a short BBD delay and into the amplifier, which puts a little reverb on it as well.

It's a typically crappy recording (I'm not really optimized for recording right now) and it's musically questionable. Bear in mind that everything but the keyboard encoder, Dark Star, VCO4069 (which is on loan to me) and Tri-phase is on breadboard. I find this sample interesting because the slow sweep of the tri-phase gives almost a 'flangy' type of texture to the background.

I didn't use the QFG section of the module on this sample, BTW. Not enough alligator clips =0).

TriPhase Sample 1 (575 KB)

This next sample uses just one VCO, VCO3. One phase of the Tri-Phase is modulating VCO3 and another is modulating the MS-20 VCF clone. There is a little additional triangle modulation of the VCO for a little vibrato.

One phase of the QFG is modulating the frequency of the Tri-Phase LFO. I play a few different random notes on the keyboard to change the base frequency of the VCO.

The VCO3 sawtooth is fed to the lowpass input of the Synthacon VCF clone, and the triangle wave is fed through a Ken Stone Wave Multiplier to the high pass input of the Synthacon clone. The EG is modulating the cutoff of the MS-20 clone with each note played (slow attack and decay).

TriPhase Sample 2 (439K)

This next sample uses the same setup as above, only another phase of the Triphase is modulating the Synthacon VCF clone as well. There are different settings on the controls, of course. This is just one held note (no keyboard manipulation). No delay or echo is used. This sample rather demonstrates the interesting VCO pitch-filter frequency juxtapositions that can be obtained when using multiple phases of the same LFO waveform.

TriPhase Sample 3 (479 KB)

The next sample is again pretty much the same patch, but with the addition of one phase of the QFG modulating the MS-20 clone VCF as well as one phase of the Tri-Phase modulating it, and only the slow attack EG modulating the Synthacon clone. There is a fair amount of knob twisting done here (just the frequency control on the Tri-Phase). A few different notes are pressed on the keyboard.

TriPhase Sample 4 (523 KB)

The interesting thing about multi-phase LFO's is that trying different phases for the same control yields quite a different flavor to the sound. Ideally, with multiple phases, having a huge selection of modules to be driven with the different phases is a big plus. For example, having several VCA's, one could crossfade or pan using the waveforms. Multiple filters, phasers, and PWM in parallel are other applications one could do. I don't have that many modules at my disposal yet, but even with a limited number of modules, this module still proves to useful in producing unusual sounds.

This next sample uses the Quadrature Function Generator section, a Ken Stone Wave Multiplier, a Ken Stone Synthacon Filter clone and a Rene Schmitz MS-20 Filter Clone to produce some Munchkin like formant tones. VCO3 is fed through the Wave Multiplier, then through the Synthacon VCF low pass input and then through the MS-20 VCF in low pass mode. The two VCF's are controlled by the QFG, and the EG.

The first part of the sample plays a note sequence, then plays the same note sequence an octave up. During this portion, the same phase (0 degree phase) is modulating both filters.

The same note sequence is played again, first low and then high, but in this sequence, the 0 phase of the QFG is modulating one VCF, while the 90 degree phase of the QFG is modulating the other filter.

When listening to the two samples in sequence, one can tell that there is a different quality to the portion that has the quadrature modulated filters. To me, it sounds more 'glottal'.

QFG Sample 1 (414 KB)

Here is another 'comparison' sample. In this sample, the Ken Stone Wave Multiplier is modulated with the QFG. It is driven through the Rene Schmitz MS-20 VCF clone. In the first part of the sample, the same phase of the QFG is modulating the Wave Multiplier Folds and Offset inputs.

In the second part of the sample, the 0 degrees phase is modulating the Folds input, and the 90 degree phase is modulating the offset input. The quadrature modulation adds a thickening and 'ringing' to the tone.

QFG Sample 2 (465 KB)

Fun With Ray Wilson's Sample and Hold

I've found using a sample and hold module to be very fascinating and useful. Sample and hold modules can produce CV outputs that vary wildly in randomness, depending upon what you feed them with. A noise input will obviously give the most random output, whereas a waveform such as a sine, triangle, pulse or ramp will give less random and more predictable results. Feeding one of these waveforms into the sample and hold can give wildly random results, but you can also find 'sweet spots' where a very rhythmic and musical pattern will result by adjusting the frequency of the input, the sampling frequency, and other parameters.

Ray Wilson's Sample and Hold is quite a nice little design, and a breadboarded version was used to make the following samples. It has an internal sampling clock, provides an offset control for the output, has a glide control for the CV output, and also input attenuation. It outputs the CV, and a trigger and gate signal to synchronize other modules with the sample and hold. I've found it easy to modify to accept an external trigger input as well.

The following samples are a sequence of basically twiddling with the sample and hold. Each sample picks up from where the previous sample left off.

VCO3, which is given vibrato with a triangle LFO, VCO4069, and the DSC2000 are each fed into the Ken Stone Synthacon clone filter. The Synthacon filter is modulated with both the Ray Wilson AR EG and the CV output of the sample and hold. The signal from that filter is fed into the Rene Schmitz MS-20 Clone filter, which is modulated in the same way. The sample and hold is fed a triangle LFO waveform. It's gate output is gating the DSC2000, and it's trigger output is triggering the EG. The keyboard is not used in these samples.

This next sample is a less in-your-face example of the Sample and Hold playing a weird, off the wall little melody. It's pretty much the same patch, with the VCO's retuned and a BBD delay thrown in. As it progresses, I adjust the decay on the EG.

Sample and Hold number 4 (530 KB)

This next sample is a more percussive variation on the patch of the first three samples, with a different tuning of the VCO's and filters. There is little input attenuation on the triangle wave feeding the sample and hold. That, in combination with the VCO's using the LP, BP, and HP inputs of the Ken Stone Synthacon filter and the DSC2000 being driven linearly while VCO3 and VCO4069 being driven exponentially contributes to an effect of different 'voices' being played in sequence. It's self-running, with no knob tweaks. It's fun to listen to this patch for a long time (longer than the sample), as it evolves quite nicely.

Sample and Hold number 5 (520 KB)

And finally, this next sample is yet another variation of knob settings with the same patch. No knobs twiddled, self-evolving, weird with a definite twisted beat.

Sample and Hold number 6 (523 KB)

This next sample is of the Sample and Hold being used in conjunction with a Small Stone Phase Shifter clone that I have breadboarded and modified to accept CV. I recorded this a while back, and wasn't paying a whole lot of attention to the levels, so it tends to be a little noisy. But still, it's a good example of the Sample and Hold transforming a phase shifter into something quite different sounding. The Small Stone clone is set in 'color' mode with very high resonance, so that it is actually sounding notes and percussive sounds. VCO3 is in the mix as well as the MS-20 clone filter. I use the keyboard to change the general pitch every so often.

Small Stone with S&H (523 KB)

Blacet Dark Star Chaos 2000

Last summer, while rummaging through some chips I'd bought back in the 80's, I ran into to two SN76477N IC's that I'd bought at Radio Shack and promptly forgotten. Not much later after that, John Blacet produced a run of Dark Star Chaos 2000 PCB's just for guys like me that still had this long discontinued chip lying around. Naturally, I lunged for it, and today am the proud owner of a Blacet DSC2000. Well, of a populated PCB anyway. The front panel is still a Hershey Bar in my back pocket. Don't ask, BTW, the other SN76477 is reserved for a Thomas Henry Supercontroller module, which only now is a gleam in my eye =-D.

Back to the DSC2000 - cool module, hands down. It seems difficult to find any sound samples of it on the web, so I'm putting a couple of mine here.

This first sample is using the DSC2000 strictly as a controller. I put in the modification to output the noise generator as a separate signal. In this sample, the noise output is modulating VCO3 and the MS-20 filter clone cutoff with random pulses. Additionally, the DSC2000 VCO output is modulating VCO3 and the MS-20 Clone through the keyboard modulation input. There are two notes played in the sample. A low note that is held and then glides to a high note. The Ray Wilson AR EG is set for a slow attack and decay, and the DSC2000 EG is also set for a slow attack and decay, but a shorter decay then the AR EG. The noise output is not affected by the DSC2000 EG - it's on all the time. So the net effect is that the VCO is gradually thrown into chaos by the VCO output of the DSC2000, then that effect dies away and you have a watery, Morse-Codey (not a real word) effect towards the end. Warning: don't start off too loud -it builds up.

DSC2000 Sample 1 (418 KB)

In this sample, the DSC2000 is the sound source. It's a simple patch, with the noise modulating the DSC2000's internal VCO. Though it is by no means a V/Oct VCO (it's closer to a linear VCO), one can still improvise some twisted melodies on it with a keyboard CV plugged into the control input of the VCO, which I do in this sample.

DSC2000 Sample 2 (425 KB)

In this one, VCO4069 is the drone, VCO3 is the lead, and the DSC2000 is the bees. All go into the Synthacon VCF clone's various inputs, through the MS-20 VCF clone and on through....

DSC2000 Sample 3 (606 KB)

Coming Soon:

The story of my Thomas Henry Digital Keyboard.