Eurorack is a type of modular synthesiser. In a non-modular synthesiser the various functional blocks that generate and modify sound (such as oscillators and filters) are preconfigured — they are connected in a predetermined way. In a modular synth these blocks are connected manually using patch cables. This makes them harder to use but more flexible. It also makes them expandable; if you need another oscillator you just buy another oscillator module. There are several different modular synth formats. Eurorack is popular because it is open, the modules are physically small and there are many hundreds of modules to choose from, from a large number of manufacturers.
I’m going to need a bunch of utility modules to make this system usable and moderately flexible.
First I’ll need some Voltage Controlled Amplifiers. I will try to make do with two dedicated VCAs (since the Z3000 oscillator has an in-built VCA) and am going with the Doepfer A-132-3 DVCA. This is a dual VCA with separately switchable control scales: linear (for CV amplification) and exponential (for audio amplification).
A non-Dalekable modular is no use to anyone so I’m including the Doepfer A-114 Dual Ring Modulator.
It is sometimes necessary to connect an output to more than one input. You might want the LFO to affect the filter cutoff of both oscillators for example. To do this you need a “one-in, many-out” module called a Multiple and I’ve picked the Doepfer A-182-1 Switched Multiple module for this task. The simplest multiple is just a bunch of jacks that are all connected to each other to form a bus. The A-182-1 multiple has two busses and eight jacks with switches that can connect each jack to bus 1, bus 2 or disconnect it from both busses. This makes it a little more flexible than a fixed multiple.
When using more than one oscillator or other sound source the audio outputs will need to be mixed at some point. I could do this with an external mixer but I think the system will be a lot easier to work with if it has at least a simple audio mixer built-in. The Doepfer A-138b Mixer is a simple four-channel mixer which should do the job. The ‘b’ means that the pots are exponential which is what you want for audio. Consequently there is a A-138a as well on which the pots are linear and more suitable for CV mixing but I don’t think I’ll need that (famous last words).