Friday, 11 November 2011

Feedback Looper

A DIY expander for the Doepfer A-112 Sampler/ Delay/ Wavetable Osc.

Since re-buying the A-112 earlier this Summer, it's become a frequent feature in my music. The one thing I wished it had was a built-in feedback function for delay duties. This can be patched, but ties up a mixer, usually a four-channel, 8HP one. This passive 4HP mixer is dedicated to that task. It also incorporates a mod to bypass the A-112's filter and AC-coupling circuit which allows one to record and process CVs.

The source signal is mixed with the output of the A-112 via resistors. Feedback is controlled via a pot. A mult of the return signal is used as the main output. You can download the schematic and extra pictures here. Experiment with the values of the resistors to get the best results for your set up. I'm sure an active circuit would have been better, but to paraphrase Nicolas Collins: if it works and doesn't smoke, don't sweat it!

As with Bitsy, I used a PCB blank, this time from MFB. Thanks to Schneidersladen for the spare Cliff jacks and Cwejman-style knobs. They're D-shaft, but that's nothing a quick blast with a drill can't solve.

Today's Patch of the Day is a jam with two feedback paths: the output of the A-112 was first sent to the A-199 spring reverb before being returned to the mixer. The oscillator was the A-143-9 QLFO, itself receiving a little feedback to bend its sine into a triangle.

DIY can be fun and frustrating but it's worth the effort, especially if you end up with a module that meets your own needs. As ever, the usual disclaimer: modding your A-112 will void your warranty, carry out at your own risk!


makro said...
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Navs said...

Link fixed - enjoy!

makro said...

thanks a lot!