SSM2024 experiments

[Haible_Juergen#Tel2743]

Hi!

Recently, I did some experiments with the output voltage
range of a SSM2024.

Background:
As I have posted some time ago, the famous SSM2040 filter
sound is partly due to its nonsymmetrical clipping, when the
ota output (!) is overdriven. This is because it has a very simple
internal stucture that saves two current mirrors in comparison
with a 3080. The output of a 2040's gm cell covers a range
of -0.5V to +14V (with +/-15V supply)

Now the simplified schematic of the SSM2024 quad VCA shows
a similar structure. This brought up two questions:

(1) Could we build a good replacement of a 2040 with the 2024
and external darlington buffers?

(2) Could we use the 2024 with a voltage output (instead of current
into virtual gnd summing node), by just introducing a positive
dc offset at the output (as in the CEM3320 filters)?

I was eager to find these answers, but only recently I found the time
to try it out.
And, alas, it does *not* work. The output stage of the 2024 must be
more complicated than the simplified schematic in the data book
would suggest. The (measured) output range is from -0.5V to
+2V only. Might be good for some unsymmetrical clipping
experiments, or for a *slight* dc offset if you want to use ordinary
polarized elkos, but that's it.

Well, at least now I know (and hope you found it interesting).

JH.