Hello all,

I have searched through the archives and haven't seen
anything like this, so I thought I'd ask everyone.  I
would like to build an audio pre-amplifier with a PIC
to control the user interface so that it is remote
controllable and so that I don't have to use a plain
knob-type input selector.  I would like to keep the
signal path away from mechanical switches which can
dirty over time or be noisy.  I was thinking of doing
something like this to accomplish the switching of
components, but I don't know if it will work:

                               ^
                               |
                              RC
                  +12__   _____|
                       \_/     |
          |---|    |----|      |
Buttons---|   |----|       in--O/A>----out
          |PIC|    |----|      |
          |   |     ___/-\_____|
          |---|  -12           |
                              RC
                               |
                               V

That's an awful drawing...The idea is that the PIC
reads the buttons and sends one line high.  Each line
(I've only drawn one) corresponds to one input.
Sending that line high will turn on a couple of
transistors that provides one opamp (O/A) power.  The
RC's to ground are to provide some amount of soft
on/off for each line.  Each line in (CD/DVD/tuner...)
has its own op-amp unity gain input buffer stage.  The
input buffers are all joined at the output.  So, I am
thinking that without power applied to the op-amp very
little signal will pass and so only the signal desired
makes it past the buffer stage and onto the rest of
the circuitry.  Will this work the way I'm thinking it
will?  Ideally, the line coming into the "off" opamps
will be muted to below the noise floor of the line
turned on (-100dB?).  Can I damage an opamp by
providing input signal w/o power?  If this doesn't
work, would a solid state relay work?  Any suggestions
as to components to use?

Thanks for your help!  I've gotten lots of good
suggestions form reading the archives!

Josh

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