DRM1 MkIII Bassdrum pitch mod

Ever since I had the Vermona DRM1 MkIII I found the pitch range of the bassdrum a bit over the top. The range of pitch I usually use was covered probaly only by 1/8th of the potentiometer range. So finally it was time to adress that issue.

After some poking around in the circuit with a multimeter I found that the poti acts as a crossfader between VCC+ (~ +9V) and VCC- (~ -9V). I then found that the pitch range that I am after lies between +5V and +9V.
So the solution seemed farely easy: configure the poti as a crossfader between those two values. This means to connect the “negative” input to +5V instead of -9V.

To achieve the above I had to cut the trace between the negative poti input and the VCC- pin of the TL072.

I the next step I installed a 1:1 voltage divider comprised of two 100k resistors between VCC+ of the TL072 and ground. The tap of the divider connects to the “negative” input of the poti, which was previously connected to VCC- and where we┬┤ve cut the trace to on the top layer.
This now applies ~4,5V to the “negative” poti input as the lower level.

And this is how it sounds

 

And, as always, a disclaimer: If you apply this mod to your own unit you do it at your own risk. I cannot be held responsible for any damage your device might take in the process.