Mega Percussive Synth

Analog percussive voice (20HP)

Based on:
Mega Percussive Synthesizer by Thomas Henry.

interactive version

My Eurorack version of Thomas Henry's Mega Percussive Synthesizer, with some very minor hardware tweaks and a custom FR-4 panel.

Build notes

The first run of this PCB has a few minor issues that are easily fixed:
1. The Decay pots should have pins 2 and 3 (center and CW) tied together - there are solder bridge pads provided for this.
2. The Noise Q potentiometer has been wired in reverse, turning CW decreases (CCW increases) resonance.
3. R1, which sets the trigger threshold at the Lock switch, is mislabeled as 33K on the silkscreen (should be 3.3K but either works).

I would recommend the following mods for 12V supply or to taste:

  • R63, R68, and R73 as 75K or 68K instead of 100K. These seem almost required because the pitch doesn't go really low otherwise, especially Shell.
  • Increase R53 to 47K or even 68K to remove a bit of the top end from the Shell pitch. With 68K the pitch still goes above 3 kHz (almost C8, more so with CV or sweep), which really is plenty for a drum.
  • Reduce C1 and C2 to 330pF (or even less?) to give the Noise frequency a bit more top end. I reduced R19 to restore a bit of low end as well.
  • Up the output mixer gain by reducing R90-R92 and increasing R77, the voices aren't really loud and they have level controls anyway (I went for 1.5x instead of x0.5).