[sdiy] SSM2164 stability

[Tom Wiltshire]

Olivier,

Three questions, three answers, and a couple of observations. Hope some of it helps.

> Since the SSM2164 is the topic of the week... What's the story behind
> the 500R / 560pF or similar at the input of the SSM2164? The datasheet
> states "for stable operation", and it looks like a passive 10kHz
> low-pass (with a zero that flattens out the attenuation after 500kHz),
> but why?

I don't know. Does the simplified schematic on Page 7 of the datasheet give any clues as to what it does?

> Have you encountered any situation where it actually had a
> noticeable impact on the output?

No.

> or in which it totally screwed the circuit when left out?

No.

One thing I have tried though is to parallel the inputs of two SSM2164s together (in order to make a stereo VCA fed from a mono signal - one VCA for left, one for right). In this case I used a single stability network, since two would have been silly. The circuit works fine. Finally I usually use 470R and 470pF rather than the datasheet values since I find them more convenient (commoner/easier to find) - again, this makes no obvious difference, or hasn't as yet.

T.