DIY and Pre-Assembled Eurorack Products


[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 modular synth stuff - 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 engineering etc. (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):

its broken D:

When it all goes wrong even if i did say this before, this is worth stating clearly:

turn it off.

dont turn it back on.


not until:

i) you have found the problem, or,
ii) you have a way of testing that wont cause damage.

note, 90% of the time when you hit power and it doesnt work you have plugged a module in wrong. most of the remaining 10% of the time its a blown fuse.
if you turn power back off quick and havent got any really vulnerable modules in your setup, you can get away with plugging in upside down or offset.

Plan A: not the fastest or most fun, but is the safest, and involves checking every module on at a time to see if it works on its own in the case - i.e. unplug everything and only plug in one module at a time then hit power, if there is any problem with either the module (e.g. no sound, no lights etc) or problem with the psu (e.g. no lights or smoke etc) immediately switch back off. even if this is done starting with the latest addition/change to the case and working backwards there are risks and it increases the chances you might plug in a module wrong due to so much messing about.

[Plan B is check all the power connections, and then, once you have checked all the power connections then you can try the power, IF you havent already killed something, i.e. you managed to avoid leaving the power on too long initially. chances are you dont know this for sure so it may be wiser to follow plan A.]

Plan B: whilst you still have power off, check the power cables of everything, starting with the newest addition/change and working backwards, to make sure they have +ve/-ve correctly aligned even if any keyed headers seem to match up, and also check the pins all line up right - its also possible in some situations to transpose the whole power cable up/down/left/right by a few pins. once you are sure you have everything plugged in right hit power and be ready to turn it off fast if there is any sign of trouble such as busboard/psu lights unlit, modules smoking etc

whether you followed plan A or B, once you have decided there are no blown modules in your system, and have everything else plugged in right, if it still doesnt work chances are you have blown (one of?) the psu fuse.

if you have followed the instructions above and it still doesnt power up, again, turn it off quick! the less time there's power when something is wrong the better in general. better to search the forums/irc/ask friends/etc for help and spend a few hrs without modular than doing more damage by rushing.

its not broken but there's no sound?

after you get your modular going, at some point you're gonna be patching stuff and suddenly it wont work - i guarantee, it's gonna happen.

before you get that horrible sinking feeling in your stomach where your head is going 'halp! i blew up my best friend', read this:

although the only general rule with modulars is 'dont follow rules', i.e. be creative in an intelligent way when everything is working, when there's a problem the rule is always 'have patience and use logic'.

This post is making some general assumptions again:

i. when you installed your modules into the case you followed info from manufacturers and the stickied threads about power etc, hence plugged in modules correctly without blowing anything up.
ii. you have got the basic minimum of modules required to make a sound - i.e. bare minimum is something that oscillates at audio frequency, and most likely a set up like this

to find the trouble, it helps greatly to follow this process - basically working through the signal path step by step:

a. plug just the VCO straight out to your mixer/interface. there should be a constant tone produced (check frequency and waveshape etc - you may have it outputting below audio frequency for example?)

b. now plug your control device, i.e. whatever you use to provide the 1v/oct signal to the VCO pitch cv in. you should still hear a constant tone, but the pitch should change when you press a key or a sequence runs. (if nothing happens to the tone, try using an alternate cv source like an LFO - this will help you find out if the control device is sending a signal)

c . insert the filter between the VCO output and your mixer/interface. when you adjust the cutoff and resonance you should hear the continuous tone from the VCO change (depending on the filter settings you might get a piercing squeal with hi resonance or no sound if the filter is attenuating the frequency output by the VCO)

d. send a gate signal to your EG and the output of the EG to the filter cutoff. each time you send a gate signal the EG should shape the filter sound (a fully open LPF can't open more - nothing will happen when you send a positive envelope. also check any cv amount knobs - if they're at zero then the cv from the EG wont do anything.)

e. insert a VCA inbetween the filter and your mixer/interface. move the working signal from the EG to the VCA cv input. there should no longer be a continuous tone (if there is you probably have some gain/initial/offset /etc. knob turned up too far on the VCA). now when you send a gate signal the previously continuous tone from the VCO should, depending on your EG settings, become audible then stop again. (long attack will take time to become audible, long release will take time to die away).

if you have progressed this far, and your basic patch is all behaving then you can test any individual modules or parts of a patch in the same logical fashion - switch audio generating modules or cv generating modules with the VCO or EG etc. as appropriate and wiggle some knobs to see if they are behaving right - since you have checked everything else it should be easy to identify a problem such as one knob silencing the sound or one output/input distorting the sound etc.

this same technique applies to any patch, but be very aware, once yu progress past this basic 'East Coast Patch', you will find that often one knob affects multiple modules in the patch, there can be dead spots where the phase of a particular wave cancels out another etc. not everything works at every setting.

WARNING!!! this technique is grand for testing things/tracking down errors/investigating new modules or patches whilst in a framework you know works or behaves very predictably, BUT, please - dont take this as a setup you must use to create every sound - there's so many other ways to patch your modules!

at the very least try patching your LFOs, other VCOs, EGs, Sequencers and even VCAs into whatever cv in you can think of - and when you've explored these avenues, try FM (audio frequency oscillators as cv sources) , using envelopes to shape other cv sources rather than just supplying a cv directly etc. etc. etc.

short of patching output to output or someother module specific not to do's that manufacturers warn about, do ANYTHING!!!

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 do stuff [***dont fool with mains electric unless you know for certain what youre doing***].

these links may be of interest/use to many: