Cyclone Analogic Bass Bot TT 303 Audio Click Problem

This one in via Tim Webb of discchord.  He wrote in to let me know he discovered a clicking noise when triggering his Cyclone Analogic Bass Bot TT-303 via an external MIDI sequencer.  I brought in Lorn Hammond, aka kidtronic, and Robin Whittle who produces the Devil Fish mods for the original TB-303 and plans to make them available for the TT-303.  Robin was able to confirm the problem.

via Robin Whittle's Real World Interfaces:

"When playing closely spaced notes via MIDI In, there may be clicking noises. These are moderately loud and have sharp edges, so they are quite audible. Please see this waveform: click-fix/click-pink.jpg . The magenta part of the waveform illustrates where the click occurs - the VCA gain suddenly drops to zero at the start of a new note, which in this case is while the decay tail of the previous note is still going. The previous note probably ended around 15:228 and the new note probably started around 15:230.

These clicks were reported to me on 2013-02-03 and the next day I reproduced the problem on our machine, determined the cause and wrote to Cyclone Analogic about it. I devised a relatively simple two component change for the circuit which solved the problem on our unit. I expect this would work well for all Bass Bots. This is not solvable via firmware changes. My suggested fix can be done without changing the PCB. Cyclone Analogic have asked me not to post any modifications to their machines, so I won't. However, for a technical description of the problem, please see: click-fix/ ."