[sdiy] Using SSM2164 in stereo

[David G. Dixon]

Tom, I don't see what you would gain by having two sets of stabilizing RC
networks in parallel.  Just split the currents after the network, and you
should be fine.  The VCAs are very well matched, so each VCA should get the
same amount of current.

The 2164 is notorious for exhibiting very high frequency oscillations when
it's gain is pushed much above 1, but if you are using it only as an
attenuator (i.e., you never expect the VC to be less than 0V), then you
should be fine.

> A quick query about the SSM2164;
> 
> I'm designing a dual stereo VCA based on this chip. Each input is fed
> to a pair of VCAs, which control the Left and Right signals for that
> channel. The two Left outputs and two right outputs are reunited in
> the I-to-V amp after the SSM2164. This makes the whole design one
> SSM2164 and a dual op-amp.
> 
> The datasheet shows each VCA input with a 500R and 560pF cap to
> ground. If I'm tying two channels together, can I dispose of one set
> of R & C? might I need to tweak the values a bit to ensure stability?
> 
> The VCA will be fed by a current output, so I don't have the 30K
> input resistor that the datasheet also shows.