Last year I began my adventure into the world of modular synthesizers by building a PAiA 9700 modular synthesizer. The 9700 is a DIY kit consisting of a MIDI to Control Voltage Converter, Voltage Controlled Oscillator / Modulator, Voltage Controlled Filter and Voltage Controlled Amplifier. These are the basic building blocks of synthesizers whether modular or all-in-one units.
There are several different size formats for modular synthesizers;
Eurorack is by far the most popular. The modules are 5.06″ tall, utilize 1/8″ connector jacks (like iPhone headphones), are crammed with features and have very colourful and busy faceplates. They also run on +/-12 volt power supplies.
Moog Unit modules or MU (or 5U) are based on the early Moog Modular synthesizers. The modules are 8.75″ tall with varying widths. MU modules use 1/4″ interface jacks (like guitar cords). They tend to have a more uniform and conservative appearance as well as larger controls with more space between them. Most modules have one or two specific features. MU systems generally operate at +/-15 volts.
The PAiA modules are in FRAC format. These modules are 5.25″ tall and like Eurorack utilize 1/8″ jacks while cramming lots of features and small controls onto each module. These modules are designed for +/-18 volts but can operate at +/-15 volts with slight modification.
This is a very basic outline of the various modular formats. For more information you can follow this link.
Each of these different formats can work together providing you use the correct cable types. Each format, however, must have its own appropriate power supply.
Personally I prefer the Moog Unit format. I like the clear, clean, consistent design of the panels. I find the larger plugs and knobs easier to handle and I find their overall appearance quite impressive. Late last year I began to build a new modular synthesizer by Synthesizers.com. In addition to the Dotcom system (as they have come to be known) I also build DIY modules by Oakley Sound Systems, Yusynth, Cat Girl Synth, Moogah and others. These modules provide the basis for a very powerful sound sculpting platform.
I wanted to make my existing PAiA system part of that platform. At first I tested the two systems together by cross patching them. The two modulars work well together but what I really wanted was full integration. While surfing the web I ran across a modular builder at Guitarfool.com. He had created custom made panels for his PAiA 9700 modules and remounted the PAiA electronics into these panels as well as replacing the 1/8″ jacks with 1/4″ jacks. I got in touch with him and he outlined some of the things he had done as well as providing me with his panel graphic. Thanks for all your help Jeff!
The first module I wanted to convert was the 9720 VCO. This module is actually two Oscillators and an Attack / Release Modulator. I made some modifications to the graphic and had a panel screened. I used a Synthesizers.com Q133 quad panel. This ensured a consistent look for the modular and a proper size fit.
The next step was to prepare the 9720 to accept +/- 15 volts as output by the Dotcom’s power supply. This involved removing R1 and R2 on the 9720 and replacing the resistors with a piece of wire. You can also connect wires between the resistor points to short them out, however, leaving the resistors in place means that there will still be resistance along the electrical path. Thanks to Scott at PAiA for clarifying this info. Finally I replaced the power connector with a Dotcom compatible connector. Both ground lines from the 9720 must be connected together then connected to the Dotcom’s single ground line. With this done and tested the time had come to swap panels and jacks.
Disassembly didn’t take very long. Fortunately the potentiometers did not require having their flying wires desoldered which saved quite a bit of time. Some of the pot to pot connections had to be severed due to length constraints then reconnected once moved.
Because the jacks were all being replaced I desoldered all the flying wires connected to each 1/8″ jack.
Following PAiA’s build document for reference I first added the new 1/4″ jacks, connected the ground leads and then (after repositioning the potentiometers) began connecting the specialty connections such as the capacitors, resistors and cross connections between jacks. I then ensured that all the connections to the potentiometers were back in place. Finally I soldered the flying wires back to the new 1/4″ jacks.
With the system rewired I first tested the module on my bench power supply. I highly recommend a separate bench-test power supply to anyone doing DIY modules. In case something has gone terribly wrong the bench supply will short out rather than your modular power supply and any of your modules. Personally I think it’s worth the extra expense.
With the module tested and working it was time to install it in my modular.
My inventory of 25mm knobs was low but I plan to replace all the knobs so that they match the rest of my modular. The larger knobs are also much easier to manipulate than the tiny PAiA knobs.
I’ve already designed a graphic for the PAiA 9710 VCA which is my next conversion project. Before that though I have a few new modules to build.
EDIT: VCO with nice chunky 25mm knobs