rainbow bridge

MODULES with corresponding design/inspiration

Noise Generators
- MIDI Oscillator - based on MDCO-3 Chip from MIDIMUSO
- FM 'Nintendo' Poly Synth - Arcano Systems Kit with custom wrapper circuit
- CEM3340 VCO - Look Mum No Computer
- Yamaha TX81Z
- Tri-oscillator drone - inspired by Look Mum No Computer
- White Noise - Ray Wilson

Filters
- 3 * CGS30 State Variable BandPass Filter - Ken Stone
- Vactrol Controlled CGS30 Band Pass filter - based on Ken Stone Design
- Music From Outer Space LPF with LFO - based on Ray Wilson Design
- Vactrol controlled 3-Pole filter - own design Sallen-Key filter
- Vactrol controlled 2-Pole BPF Filter with built in LFO - own design.
- Manual Control 4-pole LPF - own design
- Vactrol controlled 4-pole BPF with built in LFO - own design.
- 2 * MS-20 style VCF following Moritz Klein design.
- Diode Ladder filter following Moritz Klein Design.

Sound Shaping
- 2*Low Pass Gate - Synth DIY Guy
- LFO/VCA - Nicholas Woolaston LFO in same panel as own design Vactrol VCA
- Attack-Release - Nathan Ramsden
- Reverb - 2 * PT2399 reverbs, 1 own design, 1 Ebay board.
- Sub-Oscillator ; 1 & 2 Octave Sub, based on Thomas Henry Design
- Ring Modulator - Ken Stone

LFO
- 3 * own variant of Nicolas Woolaston LFO design adapted for 'Positive Only'

Sequencer
- Baby 8 Drum Sequencer - based on Look Mum No Computer concept
- Kick Drum Synth - Ken Stone
- KORG SQ-1 Sequencer

Utilities
- 3 channel Mixer / EQ - own design based on Ken Stone
- Inverting / Non-Inverting Amp/Buffer - own design
- Splitter / Buffer - own design
- Uni-Gain Mixer - Richard Jones design
- 2 Channel Performance Switcher - own design based on Keith Emerson concept
- Portamento - based on Jesse Stevens design.

Keyboards
- Arturia Keystep 32
- Modded Casio SA-46
- Alesis Q49


FORMAT :
Voltage - plus/minus 15V
Jack Size - 1/4 inch
Power Adapter - 3 pin header
Audio Signal Level - 5v peak to peak
CV Signal Level - Positive 0 to 10V
Panel Size - Moog style 8.75 inches

In general, my idiosyncratic format has kept me away from kits or finished module purchases. As a result I think I've dived a bit deeper into how things worked with the aim of creating a playable musical device.

Suprisingly there are currently no Rene Schmitz modules in my rig right now, but I have built several of his designs over time. Reference books are Ray Wilson Make:Analog Synth and Horowitz & Hill The Art of Electronics

Synth as of September 2022
Here is my rig as of September 2022. To the right you can see my Behringer bass amp, that I currently use for the synth. The line out is used for direct recording. The vibe is definitely grungy - no attention whatsoever has been given to appearance.

TEST RIG Synth Test Box

Here is my synth test box, featuring a triangle wave LFO, a manually controllable CV with digital voltmeter, a pair of +-15v power supplies, a momentary gate button, a square wave audio output & probe and a white noise generator.


VACTROLS
A word about Vactrols; basically any CV controlled synth module normally requires a form of voltage controlled resistance, which could be a JFET, an OTA, a diode but my preference is very much the Vactrol. as you can see from my module list above.
A Vactrol in it's simplest form is just a Light Emitting Diode (LED) illuminating a Light Detecting Resistor (LDR)....thus as the LED emits more photons, the resistance of the LDR falls. So why do I like Vactrols so much ?
1- Vactrols can be precisely measured & calibrated as to their resistance when a given current is applied, thus they give nice predictable frequency response in a filter situation.
2- Vactrols are very rugged and can switch large voltages and currents, avoiding complex scaling and post-filter re-amplification.
3- Vactrols have an LED and LDR response time that to my ear is quite musical and can help smooth out the response to a jittery CV. Different choices of LED size, color and LDR type will certainly have an impact.
4- The LED circuit can be electronically isolated from the audio path, thereby eliminating any noise.

So I'm definitely a vactrol fan. I typically make mine using Red LEDs, because the forward voltage is low,about 1.7 volts and 5516 LDRs that run from from 5K to approx 800K ohms. IR Leds have even lower forward voltage so I'm about to make a batch of them and see how they work.
Here's an example of one of my vactrols - note identifier E. And also a little vactrol jam. Vactrol - note identifier E Push ME

ON PLAYING IN TUNE
I really like to just plug in and jam but with a traditional CV driven VCO it is just incredibly difficult to maintain good pitch and correct octave tracking. So my rig has a couple of MIDI audio sound sources, my Arcano NES FM synth and a MIDIMUSO MDCO-3 twin oscillator. Both are literally plug and play and the MDCO-3 in particular produces an awesome square wave that is always in tune and tracks perfectly.

However, I also really like the sound of an analog saw wave and portamento does not work with MIDI so I am planning to work on my CEM3340 VCO - Look Mum No Computer design and try to get it stable at a certain pitch with just fine tuning neccessary and maybe add a range switch for bass.






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