VCA chips

[jhaible]

> JH's interpolating scanner work inspired me to come up with some
> designs of my own, and I'm writing up an article about them that I'll
> be posting soon.

Sounds interesting !

> And so... I've been looking at the VCA issue.  JH uses SSM2024's,
> clearly a good choice for hifi reasons, but it appears from the Analog
> Devices web site (http://www.analog.com) that these are no longer in
> production and a newer chip called the SSM2164 is the one to use.

I noticed the same thing some time ago, and asked AD about the 2024's.
Back then (about 1/2 year ago), they said they were still in production,
but they recommend the 2164 instead. So it's a good idea to ask them again
about the 2024's current state.

> Okay fine; and look, the data sheet for the SSM2164 mentions that you
> they're designed to replace the SSM2024 with minimal circuit changes.
> Cool...
> Except they fail to mention that the polarity of the control input is
> inverted.  

Doesn't the 2164 has exponential control inputs ? I don't remember that
exactly,
but in that case it would be hard to use in the Scanner.

I haven't done this myself, but I highly recommend that someone tries the
CA3280 (no typo) for the scanner. It can handle much higher Iabc currents,
so one could insert the LEDs directly in the Iabc control path. (with ne
calculated
threshold voltages, of course).

JH.