DIY and Pre-Assembled Eurorack Products

Wish Someone Told Me...

[originally posted on ModWiggler formus by me many moons ago!] I seemed to be answering a lot of questions via PM, msn and email about real basic patching of a modular synth - the same stuff i wish someone had told me when i first started, but was afraid to ask and wasnt yet ready to cope with reading whole books on principles of synthesis. (so, for those with zero knowledge here's some slightly oversimplified, sweeping generalisations, for the sake of easy explanations to those who want to get their newly acquired/setup modular tested and working):

generally there's two sorts of input/output signal:
Audio - sound in the form of an alternating current (AC) at a frequency (pitch) and amplitude (volume)
CV - a direct current (DC) signal used to control stuff.
(These are not automatically interchangeable and hence trying to use an audio signal to control a CV input parameter or trying to hear a CV may not work. there are exceptions to this though, especially more so with some module types/manufacturers.)
- all cabling and signals in eurorack are mono - if you want stereo you need multiples of each module or dual modules designed for stereo!

Oscillators send a signal even with no input. even if there's nothing saying what pitch to play or when to start/stop - that is done by other modules such as sequencers, VCAs etc. This is true for VCOs - they'll make a constant tone and LFOs - they'll make a constant CV (dependent on settings)
VCAs need a CV to allow sound to pass through. unless there's an offset/initial control set to allow some audio through. In a most basic patch this CV is generally a gate triggered envelope.
- VCAs usually do not add positive gain ['make things louder']. They are more like Voltage Controlled Attenuators since they actually turn things down. Max CV into a VCA control input will set the amplifier to unity gain or 0dBv (no gain)['full volume']. 0v CV into the VCA will cause it to fully attenuate ie -80dBv ['silence'].
      * A VCA is Voltage Controlled.
      * An Attenuator has no voltage control.
Envelope Generators need to be triggered. This is generally done via a Gate signal, but can be a CV from pretty much anything providing enough voltage.
Filters can completely silence a sound. since on a basic level filters remove frequencies from an audio signal, for example, at certain settings a low pass filter may take all the high frequencies out of an audio signal that is just treble such that nothing remains.
Some filters can self-oscillate. Effectively, when certain settigns are cranked up high enough the filter can emit a sound even with no input, generally a relatively loud audio frequency sinewave.
VCAs and Filters can distort when fed a sufficiently loud audio signal. this can be a very fun thing - i love to feed the ASys RS-100 LPF and/or RS-180 VCA a really hot signal by putting a cranked up VCA or Filter with lots of Resonance before them in the signal path because they overdrive in a lovely, warm, fuzzy/growly way.
- Most Sample & Hold modules require an external input to sample, AND output a DC CV signal. at sufficiently high sample rate settings the CV output can be used as an audio source, but generally the output will be either a stepped sequence of CV signals if the sample is a wave or some random/pseudo-random CV singals if the input is noise or a very complex audio source.
To split a cv that is to control the Pitch of multiple VCOs you may need a Buffered Multiple. if you use passive multiples or stackcables, too many modules drawing from the same pitch source may affect the voltage causing tuning to be off. you can get away with only a few splits with a passive multiple/stackable, sometimes.
Buffered Multiples have designated ins/outs - these wont work like a passive multiple. you can't get a signal out of an 'in' or put an in into an 'out' with a Buffered Multiple.
- Some modules can be very sensitive to tiny changes in CV or settings, others can require quite big changes to get any significant difference in output. CVs and Audio signals can sometimes need attenuation or amplification as a result, and sometimes a DC offset can be necessary to allow CV's/Audio signals to be used interchangeably. some modules have controls such as 'Gain', 'CV' amount and 'Offset' built in. otherwise, a dedicated Attenuator, a VCA or an Offset module may prove a valuable, if not essential component of a system.
Audio can come out much louder or quieter than expected sometimes. there's a myriad of reasons, but to pick just one example, if you have certain wave forms being mixed together, phase cancellation can take place in certain circumstances, resulting in dead sounding quiet zones when sweeping through settings. your module isn't broken. modules like the Doepfer A-136 are absolute sods for this, and they are so sensitive i find that using attenuators in the signal path before the CV inputs can be invaluable since it's so sensitive at some settings...
- Cheaper Ring Modulators tend to be AC-coupled. this means they dont work on CVs. for this you need a DC-coupled Ring Mod.
- something i have just been alerted to: on doepfers homepage where the standards are laid out theres no mention of pitch cvs. generally pitch cvs are between 0 and +10V, but not all vcos can respond to/accurately track the full 10V range. this is why many quantisers dont accept -ve cv values!

to test and get comfortable with new modules or a new system, it helps to use this absolute basic patch:


You will require a sequencer/Cv keyboard/[computer/midi source plus midi -> CV device] to produce 1v/Oct note CVs, Gate signals and so on, unless you want to use LFO's and other modules.

This patch will give a standard 'monophonic, note follows note at given pitch, with given length' synth patch. To test other modules most effectively, try patching their cv outs to the Filter cutoff or the EG Decay time for example.

p.s. You're using a modular - rules are meant to be broken; with the exception of manufacturer warnings about specific module settings, inputs and outputs that dont like being used in certain ways, experiment! the whole point of a modular is to mess about and find unusual ways to trigger an envelope or shape a filter cut-off etc.

this link may be of interest/use to many: