The Syndrum was originally created by Joe Pollard and Mark Barton, this was the Syndrum x77 (replace x with the number of drums in the set) and there is very little information on their workings around on the internet. I managed to purchase the 478 service manual which is the updated version of the original in a set of 4.

Schematic of original

A4 PDF Version 


It is pretty typical design, trigger is taken in, conditioned then it is sent to 2 envelope generators, one for snares the other for sweeping the pitch. The LFO is a integrator and Schmitt trigger design with switches to extract different waveforms.

Shamefully the noise circuit was missing (I imagine all the drums share the same noise source) but it would probably have been a standard reverse transistor circuit (see Synare for ideas.)  it could have also been a shift register style noise source. What is interesting is the noise gate circuit, 3 diodes and some resistors saves on another OTA chip!

Because the PCB does not have a silkscreen I excluded pin numbering, if you are testing the original remember that the op-amp is not a standard 1496 quad op-amp but a RCL4136.

The actual voice comes from an ICL8038 precision waveform IC with a bit of extra circuitry to make it more musical.

DIY Schematic

The ICL8038 is rare these days (your looking at £25-40 to buy one) so a DIY version is going to be very expensive. But if you must or you have a few 8038 hanging around (I do!) Then watch this space. Mods to the original are not really recommended, sell it!! buy a Yacht.