Eurorack implementation of circuitbenders.co.uk CB55

Symmetrizer eurorack implementation of https://www.circuitbenders.co.uk/forsale/CB55/CB55.html

"The circuitbenders.co.uk CB55 is an exact clone of the voice board of the Boss DR55 drum machine. It has the four fully analogue percussion sounds, bass drum, hat, snare, and rimshot, but leaves out the clunky and arguably useless sequencer. There is also an overall accent feature that adds a little extra punch to the whole mix when it is triggered."

I've added LEDs for triggers, op-amp based amplification of the voices to get them up to eurorack compatible levels and finally a switching circuitly which detects if a cable is inserted in the individual voice out jacks and removes that voice from the mix out. My solution uses normal thonkiconn jacks, a comparator and a voltage controlled SPDT to achive this.

My implementation has mods for RS pitch, BD pitch, BD decay, SD pitch and SD Noise level

One quirk is that I've chosen the pot value for BD decay so that the bass drum can drone.