3340 stability

[Tony Allgood]

>Is this a specific problem with some 3340s or is it a problem with
external
components in the oscillator, or possibly contamination of the board
causing
leakage from the timing cap?

There are several points that need to made on the 3340 tuning stability.
Firstly, it really does make a difference what you are using it for. In
a poly synth, ie, Juergen's OB8 and my one, the tuning does indeed take
about fifteen minutes to stabilise. However, my monosynth which has four
3340s in it doesn't seem to take so long. Why? Because scaling and
absolute pitch are not so important in a mono as it is in a poly. Any
3340 will take a while to stabilise, it has to, and so will the power
supply that drives it. If you are running it off + and - 15V then it
will take longer still. If you are using 7815/7915, these too take a
while to stabilise. The Elektor polyformant used 11.05 volt and -5volt
supplies for its 3340 VCO design. Solely to reduce the heat dissipation
in the device, and hence reduce the time for stability. The box the VCOs
are in will also slowly warm up, this must have an effect on each VCO.
The top boards quicker than the bottom ones. There is no doubt that some
3340s are more sensitive to heat than others. I have one that is very
poor. I can swap it with a good one, so it is not the timing cap or
whatever, some VCO chips are worse than others. The bad one has been
confined to the emergency only pile. All I can say to Colin whose VCOs
are in tune from the moment they are switched on... you lucky thing!

Regards,

Tony Allgood, Cumbria, UK

Rack mounted moog filter and the TB3030 SuperBassline projects:

http://aupe.phys.andrews.edu/diy_archive/schematics/oakley/