Wednesday, 18 March 2009

Synth DIY - Trigger Twin Dual Comparator

First public outing for my second DIY module: the Trigger Twin dual comparator.

Inspired by Peter Grenader's Triple Event Timer, I gave up on my original LM339 design and settled on a simple Op-Amp circuit. A timing CV is fed into the lower middle jack, pots one and two are used to adjust the delay time, triggers are output from the left and right jacks, orange LEDs indicate the on and off time.

I designed this module as a companion to Doepfer's A-147 VCLFO, using the pulse output as the initial trigger and the triangle output as the timing CV. In order to fine-tune the device, I added an offset voltage which, using the Plan B vernacular, serves as a Time Base control. Counterclockwise is 'tight', clockwise is 'sloppy'.

For those of you wanting to try this at home, just consult the TL072 etc datasheet for example comparator circuits. The timing CV and offset are mixed via resistors and fed to both comparators in series (no fancy limiting or switching involved!). I brought the outputs down from 12V to ca. 3.5V with a couple of resistors and followed this with a diode to block any negative voltage. I opted to make my reference voltage zero to +12V but, of course, you might want to make it bipolar.

The parts and components were bought from Rapid in the UK, Banzai and Schneidersbuero, both here in Berlin.

Background to this project including audio is here, here, here and here.

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