Which modules and general progress

What modules to build?

One decision I am facing right now is which modules and how many. The basic studio system included:

• 1 - VCO-A - 4 wave forms, sine, triangle, saw, pulse
• 1 - VCO-B - 2 wave forms, sine and saw
• 1 - VCO-C - 1 waveform user specified to be square, triangle, or saw
• 1 - VCF - selectable HP, LP, or BP, classic...
• 1 - Dual Random Voltage Generator
• 1 - VC Trigger generator
• 1 - Triple Envelope Generator
• 1 - VCA/Mixer
• 1 - Noise Generator
• 1 - Ring Modulator
• 1- Tuner/Monitor
• 1- Input pre-amp

The Synthasystem added:

• Three Octave Keyboard
• 1 - Phaser
• 1 - Frequency Divider
• 1 - Sequencer

Optional modules included:

• Peak Selector - trigger based on the signal input level
• Dual Voltage Follower - "The voltage follower does the same thing for control voltages that the Portamento doe to keyboard voltages."
• Voltage Processor - 6 input, two output mixer. DC/AC signal compatible. Outputs A and B are the same except for the phase.
• Selective Inverter - I have no documentation on this module.

I don't have all the schematics I need for a complete Synthasystem. I'm missing the Phaser, Frequency divider, Ring modulator, Pre-amp, and Tuner/Monitor. I have the others as either original Synthasysem modules or from the Synthacon.

I'm thinking the Tuner/Monitor and Frequency divider aren't really important to the sound of the system so I could cobble something together if needed. The Phaser and Ring Modulator, however, would be unique to the Synthasystem. These ones will require some thought on what to do. When I was first building this in the 70's, my thought was to mimic a Moog system 55. The 55 did not have a Phaser or Ring Modulator, so I probably would not have built them anyway, if I do build these, I'll find something "vintage" and simple and add it.

For my resurrection, and to match the general function of the Moog 55 I wanted to mimic, I've decided to build:

• 7 VCOs. All type A to give all the waveforms.
• 5 VCAs. 
• 3 VCFs. This way, I can have one LP, one HP, and one BP
• 1 Noise
• 2 Triple EGs. This gives me 6 total EGs
• 1 or 2 Sequencers

I'll probably also add:

• 1 Dual Sample and Hold
• 1 or 2 Dual Voltage Followers. I don't have a Steiner schematic for this, but I think I can find something "vintage" to use. The Synthacon keyboard has a portamento control I might be able to use.
• 1 VC Trigger Generator. I only have the Synthacon schematic which does not include any voltage control. I will have to add this, so this won't be strictly a Steiner design.
• Voltage Processor. I'm pretty sure Nyle would have used his mixer core with some Op-amps on the inputs/outputs to provide the normal and inverted signals.
• A keyboard controller. I'm not really sure on this as I don't have the Synthasystem schematic with the legato play mode. I have the Synthacon schematic. What I'll probably do is build a module that has a keyboard CV in, and standard voltage gate in and then use the Synthasystem schematic to add portamento, voltage gate to S-trigger, and keyboard S-type gate, and maybe the pitch bend. Nyle had a keyboard interface module, and this will be similar and will let me use a modern keyboard controller like the .com one.

I'm thinking of adding some modules for which I don't have specific Steiner schematics, so I'll have to roll my own:

• Tuner/Monitor. The Tellun/Dave Brown A440 tuner and monitor would be useful here. I have an extra A440 chip, and I might even add an O-Scope like I did to my other modular.
• Phaser. If I can find a simple vintage transistor based phaser, maybe with a BBD delay, I'll build it. It won't be Nyle's, but, in keeping with my original desire, I may not have done a 100% Steiner system. In fact, I know I built a cross fader because Walter (at the time) Carlos used that effect in one of his SOB renditions.

As for the Ring Modulator, I'm not too keen on them, but if I can find a design which incorporates the same controls as Nyle's did, I might build it to fill out the box.

Panels will be Euro size. Nyle used a 5.75 inch tall and 1.75 inch width multiple panels with 1/8 inch jacks, so a Euro, or Frac for that matter, size is in keeping with the original scale and I have the advantage of being able to buy ready made power supplies and racks. I'm not sure, but I expect the finished modular will probably take three or four racks.

I want to try to keep the same layout as the Synthasystem, but will depart from it if it means substantial space saving. I will use similar, but probably smaller knobs so I can be a bit more compact.

VCO layout

I have the VCO schematic entered and some of it partially simulated. The core simply isn't working and I'm convinced it is the transistor "diode" component that is the problem. So, I'm going to try to bread board it, but I'm going to lay it out so I can use discrete components, a monolithic NPN pair like the SSM2210, or use a monolithic NPN and PNP pairs like the THAT340. I'm pretty excited for that.

Envelope Generators

I'm thinking I'll get the EG boards sometime this week. I'm excited to get them and build one as a ENVDL-1 and ENVDL-2 type. I will build a few for my other modular for fun if they work well.