Since Coolaudio started reissuing old IC’s used in various synths I always eyed the V3340, which is a reissue of the CEM3340 chip as used in many classic synths such as the Roland SH101, Prophet 5, Memory Moog and plenty of others. It’s, in essence, a fully featured 1V/oct oscillator on a single IC and thus takes away a lot of the headaches inherent to VCO design. Things like linearity and temperature compensating are taken care of for you. This takes away a lot of the pain of building VCO’s, in fact, since these IC’s are available again a DIY polysynth starts to become a possibility.
I always wanted to build a ‘clap’ sound module that’s not a one on one re-creation of the 808 or 909 and has a bit more control. I liked the sound on the Vermona DRM, so something like that, but not quite the same.
My ‘broken’ EHX Bass Micro Synth was gathering a ton of dust. After bringing it back to life I noticed all the sliders were far from performing well and should be replaced. Sourcing 10 100K linear sliders with the right dimensions turned out to be rather difficult and costly. So I decided to transplant the pedal’s guts into a 19″ rack casing from an old and broken M-Audio firewire audio interface and at the same time see how I could make it more synth/modular friendly. So, here’s a brief list of things I ended up doing to it:
- Switchable filter type (BP / LP)
- Added a square sub oscillator
- Added an external input
- Changed input/output gain behaviour
- Extended the filter range
- Added and ‘extra’ resonance switch
- Added external trigger input
- Added filter CV input
- Added Envelop follower CV output
- Added trigger output
- Added trigger/filterCV leds (the thing could use more leds)
- Added a sort of distortion/clipper
- Replaced the internal power supply with an external adapter (I really didn’t trust that thing)
So, it’s quite a list. But I’m pretty happy with the results so far. Things could do with a bit of tweaking here or there, but that’s up to personal taste. You’ll can find the schematics of the EHX Bass Micro Synth easily enough on the web, but for the lazy, click here. I’ll try to address the implementation of some mods in this article.