[sdiy] Welcome to the Twilight Zone

[harrybissell]

Two thoughs...

1) phase reversal on one of your opamps...

2) ultrasonic oscillation on an opamp

3) some flakey connection on the circuit board

any one might give the symptoms you describe.  I got hit with #3
about three years ago at AHMW.  My quantized theremin failed to
work. I field stripped it and lo, it worked. I has concluded grounding
problem at that time (I had not used it with the full PA system)

Later found that a connection on a critical voltage reference was not
soldered correctly. I use Vector T-42A pins... and the solder had
bridged the TOP of the pin but not wicked down to the lead.  Push
one way, works, another... don't work.   This impersonated another
problem.

oh yeah, I forgot #4.   I DID warn you about those "fatties in the
parking lot at lunchtime".   If I was your boss... I'd FIRE you. Since
you are your boss, I guess you'll have to make the call...   <bfg>

H^) harry

Peter Grenader wrote:

> Thought I'd share a bit of bizarro behavior which occurred late last night.
>
> When putzing around with the prototype Plan B (vector board) all of the
> knobs except the PWM and FM attenuator - the Freq, fine tune, even the two
> bipolar freq VC attenuators - suddenly operated in reverse.  Turning the
> freq pot CCW made the pitch higher.  Turning a freq VC attenuation pots
> fully CCW processed the VC fully positive (should be the other way around).
>
> Turned the power off - still there.  repeated that a few times - still
> there.  So then I put my VC Input through an external processor to invert in
> before it went to the VCO to see if I could fake the VCO out and when
> turning the offset knob on that processor in a  positive (more voltage)
> direction, I suddenly noticed that the controls returned the 'normal'
> operation on the VCO.
>
> They are all running off the same supply.  However, in the name of science
> and unparalleled universes, all of the effected controls do run through the
> same op amp internally (they are summed).
>
> Too weird and yes, I did check for flying donkeys outside and no, my cat did
> not begin to bark during this time.
>
> Now off sign to going I'm,
>
> - P