[sdiy] Unused SSM2164 cell

Neil Johnson neil.johnson71 at gmail.com
Mon Jul 20 16:58:46 CEST 2015

Olivier wrote:
> What I'm wondering is if the oscillations the compensation network is
> supposed to suppress happen spontaneously, or only in response to HF
> components (eg sharp edges) in the incoming audio signal (in which
> case they could not occur is the input is just connected to ground
> through a resistor).

If you look at the schematic for the SSM2164 you can see that the
input is actually a current summing node, with feedback from the
output gain stage.  The differential pair and gain stage behaves
somewhat like an op-amp, so somewhere in there you have a critical
pole which, without suitable compensation, will have gain at some
frequency.  So even without you providing input there is the strong
potential for oscillation at some frequency.  The external RC network
provides lead-lag compensation for that pole, keeping it stable.


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