Saturday, 19 January 2013

A-143-1 Modification

Adding voltage control and a combined trigger output to Doepfer's Complex Envelope Generator. An update to these posts (1, 2).

The A-143-1 is king of the shonky rhythm. There's something about the swing generated by its four chained envelopes and comparators that is hard to replicate with a VC-LFO and sequencer. This modification provides two features I wanted when using the A-143-1 as a wonky clock: a combined pulse stream to control other modules and an automated means of influencing the rhythm.

For the latter, I chose to add simultaneous voltage control to the threshold of all four comparators. For me, this is the parameter that makes the A-143-1 tick. It means a single CV can be used to stretch and shrink the rhythm without affecting its inherent groove. Think 'Funk Soul Brother'. Just as importantly, the modification can be accommodated on the original panel.

The Comparator outputs are chopped down to 1ms pulses, so they can easily be mixed without the need for a 'proper' logic circuit. They are also hot enough to ping filters. Add a Sample & Hold to grab values from the A-143-1's bipolar mix out and the results can sound like this:

The star of this mod is the H11F1 Photo FET Optocoupler. It may not have the cachet of a VTL5C3, but this vactrol alternative might make a better choice for some synth mods. It's smaller, cheaper and, most importantly, has a fast, linear response.

The circuitry used in this mod is simple. The difficulty arises out of the need to quadruple the parts. You can download my build-notes here (the usual DIY disclaimers apply!) to see how I went about it. See this thread for more A-143-1 modification ideas.

To close, today's Patch of the Day offers a musical example of this modification:

The patch uses just two envelopes, sometimes chained, sometimes running as LFOs. The new combined trigger was multed to ping a Cwejman RES-4 and trigger a S&H and CTG-VC envelope. The A-143-1's mixout was sampled by the S&H and sent to the RES-4's FCV and CTG-VC's Attack CV-in. The RES-4's audio output was sent to a VCA-4MX and multed to an A-199 Spring Reverb. The 100% wet signal was sent to a second VCA/ mixer channel and opened by the CTG-VC's envelope. Altering the threshold changes the timing and also the CV that is sampled from the mix output.