Odp: [sdiy] tempco puzzle

[Roman]

Maybe a NTC in series with control voltage input of SSM?
Not too precise, and probably not even linear in temperature
response, but should decrease your 3500ppm tempco
by range of 5-7, which IMHO is good enough for any VCA.

Roman

----- Original Message -----
From: Seb Francis <seb at is-uk.com>
To: synth diy <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, October 01, 2002 4:38 AM
Subject: [sdiy] tempco puzzle


> Hi,
>
> I'm building a Mixer/VCA with an SSM2018 I got lying around.  It has a CV
tempco of -3500ppm/C, so I need to build the CV input stage with a 3500ppm/C
tempco.
>
> The required gain of the CV input stage is -0.25, and I have 1K 3900ppm/C
tempcos.
>
> The question is .. how to do it with *minimum* extra components?
>
> The only way I can work out uses 3 inverting apamps:
> CVs => Inverting unity-gain summer
> => Inverting unity-gain
> => Inverting 0.25 gain with the 1K tempco + 150R 100ppm/C resistor in the
feedback loop
>
> I've been racking my brains for hours trying to work out a more elegant way to
do this, but have got nowehere (maybe I'm trying too hard over 3 opamps, but
it's nice to find the neatest solution ;-)
>
> Single opamp + potential divider with tempco doesn't give a near linear
coefficient because the gain is not small enough.
>
> There must be a neat way to do this!
>
> Seb
>
>