Precision heater chips (fixing temperature instability)?

Hi all,

I was asked by a musician if I could do something about the temperature
instability of his old Moog 342 synth. At the core of its oscillators is
the CA3046 transistor array: http://www.linetec.nl/electronics/moogosc.jpg

This design turns out to be quite sensitive to temperature changes -- as in:
at least a half tone for every 6 degrees centigrade. This isn't much of a
problem in a studio setting, with a constant temperature of some 20 degrees
centigrade, although even then, it's necessary to let the instrument heat
up internally for half an hour before playing. However outdoors, the synth
is totally useless.

I tried replacing the dual transistors with an SSM2210 matched transistor
pair (with a far better matching that the 3046), but to my annoyance, this
didn't result in the improved stability I hoped for. Perhaps this is
because the whole design isn't really symmetrical and balanced -- I haven't
yet taken the time to investigate & calculate exactly what is happening.

Anyway, it seems that it's not just the transistor matching that's
important, but also the absolute Vbe value. This latter can't be stabilized
in any way except by providing a constant temperature -- so I'm thinking
about another classic solution for cases like this: heat up the '3046's to
a precise temperature, e.g. 50 degrees centigrade.

Now I already drew up a simple design based on a TC1047 temperature sensor,
an opamp and a power transistor, to be stuck onto the transistor arrays,
but I wondered if there's a simpler or more integrated solution available,
such as a precision PTC or a special "heater chip". Or even a transistor
with a built-in temperature sensor would be nice already.

As always, thanks in advance for any suggestions.

Richard Rasker
--
http://www.linetec.nl
.

Relevant Pages

  • Re: Precision heater chips (fixing temperature instability)?
    ... instability of his old Moog 342 synth. ... This design turns out to be quite sensitive to temperature changes -- as in: ... at least a half tone for every 6 degrees centigrade. ... I tried replacing the dual transistors with an SSM2210 matched transistor ...
    (sci.electronics.design)
  • Re: Precision heater chips (fixing temperature instability)?
    ... Richard Rasker wrote: ... instability of his old Moog 342 synth. ... This design turns out to be quite sensitive to temperature changes -- as in: ... I tried replacing the dual transistors with an SSM2210 matched transistor ...
    (sci.electronics.design)
  • Re: Transistor oven.
    ... >>> I wish to use a monolithic transistor array in a circuit where the die ... >>> temperature is temperature stabilized. ... I am hoping to find a circuit ... >>thermal differentials across the die. ...
    (sci.electronics.design)
  • Re: Transistor oven.
    ... >> I wish to use a monolithic transistor array in a circuit where the die ... >> temperature is temperature stabilized. ... I am hoping to find a circuit ... >thermal differentials across the die. ...
    (sci.electronics.design)
  • Re: Precision heater chips (fixing temperature instability)?
    ... Richard Rasker wrote: ... instability of his old Moog 342 synth. ... This design turns out to be quite sensitive to temperature changes -- as in: ... I tried replacing the dual transistors with an SSM2210 matched transistor ...
    (sci.electronics.design)