Wednesday, 28 January 2009

Patch of the Day - Los Comparadores

Abusing Doepfer's A-137-2 Wave Multiplier as a quad comparator and event timer.

This had me laughing my head off: the results are just too unpredictable and the patch needs some explaining.

Have a listen first:

The background:

I'm currently attempting to build a quad event timer along the lines of Plan B's Model 17 Triple Event Timer and have so far bread-boarded a working dual comparator using an LM339. This works quite nicely, but is not ideal.

Taking a break and looking for an alternative (read: quick, cheap fix. I'm lazy, right?) I realized my A-137-2 Wave Multiplier is itself a quad comparator. Happily it will accept a DC input, output triggers of a sort and the threshold levels are voltage controllable. Unfortunately it only has a mix out but I overcame this by using a sequential switch to feed a trigger to each envelope generator.

The patch in detail:

Bananalogue VCS paces the A-137-2, A-137-2 mix out to A-151 sequential switch, +5V to its common input is fed to each of the A-143-1 Complex EG's four envelope generators, individual outs to a Cwejman VCA-4MX gating four VCOs, mix out to a CGS52 Lockhart Wave Folder and on to a VCA-2P for panning which is controlled by the mix out of the A-143-1. Still with me? I then took two LFOs (positive and inverted) and patched them to the CV ins of the A-137-2 to modulate the timing of the events.

Two oddities about using the A-137-2 for this sort of application: it's totally imprecise and the input level of the pacing CV has an effect on the timing. You can hear this in the first thirty seconds, where all I am doing is changing the input level. The Lockhart really made this patch for me: when the spacing between events is tight, in effect producing a chord, the wave folder churns out a lovely clangorous noise.

While not as precise as the M17, it's close enough for Rock 'n' Roll and, if it saves me from the soldering iron, then it'll do for now!

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