[sdiy] EFM SBM VCO CV problems still lurking

[vitreousflux]

I have a few more details to my EFM SBM VCO CV problem.

I have 3 power supplies - two are 12vAC, one is 16vAC. All 3 put out nice
sine waves when unconnected.

When any of them are connected, the waveform distorts and appears clipped -
look at this picture which is a drawing of the waveform I see on my scope:

http://www.wwnet.net/~midibear/waveform.jpg

See those notches in the waveform? that is similar to what I see in the VCO
waveform. What is strange is the notches change frequency along with VCO CV.
You should hear what horrors that does to a sine wave at higher frequencies.

In my input VCO CV (for both VCO's - they behave identical) I am gettting AC
within the CV.  However, my +12V and -12V are nice flat DC lines - some
miniscule noise but otherwise appear nice. All other modules in the SBM work
fine. This is puzzling to me

I have removed all external wiring from one VCO - only the INIT FREQ trimpot
is adjusting CV at this point - same results.  Prior, I had removed all +V
and -V jumpers to all other modules - I had only the VCO1 module getting
voltage, same result.

It's my hunch that something in my power supply is the problem?

In Tom's SBM scanned photo, In the power supply section he has smaller 0.1
ceramic caps - mine are physically larger (yet correct values). My VCO's are
essentially built identical to his from what I can see.

I am trying to get access to a good function generator to isolate the power
supply but that will be a few weeks away.


Thanks

Rob