Yamaha CS80

erikfromhere wrote:
> talking about stability:
> one of my CS80's took over one hour to get all oscillators pitched 
> correctly while my other took only a few minutes.
> So, I removed the old (and hardened)silicon-grease from the oscillator-
> ic's and applied new grease and made sure the diodes were completely 
> covered by it. 
Thanks for the info.  Remember, the diode should be touching the VCO
chip. Could I ask something of you, and others talking about this:
please include the serial number of your CS80. This will help us figure
out the stability over the years they were built.
>
> About the codes, I think it's ok to use different -non matching- 
> codes, but then you'll have to accept that during warming up the 
> pitches are uneven.
>   
Probably ok in a studio.  If you're outside and the temperature / sun is
changing, good luck.
> Of coarse, tuning the pitches should be done best on a hot summerday 
> or using a towel to keep the heat inside the synth...
>   
I put my remote-probe oven thermometer inside my CS80 with it closed up
to measure the temp inside.  Then I opened it up and turned on a heater
in the room until the temperature was close.
> Since, I'm not technical, can someone explain how the diode influences 
> the pitch of the oscillator ?
>   
Simple version.  The current in almost all electronic components varies
with temperature. The varying current affects the circuits, which is
most noticeable for VCO/pitch. The diode is thermally coupled to the VCO
chip so that it tracks the same temperature. The diode current is then
used to try and cancel out the temperature effects of the diodes and
transistors inside the VCO chip.

The Yamaha VCOs are linear (Hz/volt), which don't need the exponential
converter found in more usual exponential VCOs (volts/octave) used in
most synths.  Exponential converters are very temperature sensitive, so
the CS80 is actually much more stable than synths like the Prophet 5,
which always need some kind of auto-tuning circuits.