[sdiy] SBM VCO CV interference

[vitreousflux]

On my EFM SBM, I am getting a strange problem.

On my input CV line which consists of 1 input and 3 tune pots (freq, fine
and init freq trimmer), I am getting an odd narrow pulse-wave signal on my
scope - it changes frequency along with the signal CV.

This causes weird harmonics in the output signals (sine, tri, saw, pul) and
is most noticeable at higher frequencies.

The pulse wave seems to actually be two signals: a full cycle narrow pulse,
and a half-cycle (positive only) at 90 degrees offset. How bizarre!

I checked all my grounds and traced the problem back from the opamps, but
have no where else to check the signal - it's the start of the circuit! - I
am using no input on the cv (although have tried using a cv input which does
not help the problem).


Anyone else run into a similar problem on their SBM or analog synths?



Rob