OB-X filter CV breakthrough

[Tony Allgood]

Hi all,

I have just got my OB-Sx module racked up and ready to play. The UK
synth DIY guys know the one... the bright yellow affair I bought from
Tom Carpenter. Changed most of the pots functions and got a new panel
from Schaeffer. Sounds brilliant... I got the aftertouch doing more than
just opening the filter as well. My thanks go to Juergen for introducing
me to the idea of creative aftertouch with his awesome JH-720. My
midi-CV prototype is working well too.

Right, a question to all those OB-X (and family) owners. How good is the
CV rejection on the 2-pole filter? On my OB-Sx module, the cut-off
frequency CV bites into the audio really badly. Far worse than a
untrimmed 13700 based filter. It only does it noticeably when the
modulation is big and sharp (large dv/dt), eg. fast ADSR waveforms or
square LFO. The output of the 3320 IC sits at around a nominal 3V, which
is not too suprising, given the supply rails, but it does swing by a
large degree when Fc is varied. Is this normal?

Regards,

Tony Allgood  Penrith, Cumbria, UK

Walsh synthesiser, SuperLadder, TB303 clone and rack mounted filter

http://www.techrepairs.freeserve.co.uk/projects.htm