Well it all depends on whether you are happy with some kind of limiter or
not, with the sometimes strange effects you can get. That would be one way
to not go over a certain level.
I'm sure its not that hard to do with an op amp and some feedback.
Brian

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Brian Gaff
"TonyL" wrote in message
...
Here's a problem that is causing me some grief. I'm rusty with electronics
these days, perhaps the experts in here can give me some pointers ?

I want to combine the audio outputs of an unspecified number of op-amps,
say 2-20. A simple mixer would do the trick...except I need the resulting
summed audio level to be constant as outputs are connected to and
disconnected from the system.

I know a virtual ground is the standard method to mix audio but there's
another wrinkle here. I also need to send the summed audio signal to an
unspecified number of outputs, between 2 and 20. In other words, the
common point where all of the audio signals are present needs to be level
insensitive to changes in numbers of audio inputs *and* outputs.

Is this possible ? I've tried some breadboarding and find that each added
input results in a level drop at the "star point". Also, adding a second
virtual ground output completely kills the audio. I can, of course, add as
many outputs as I wish using the output op-amps as high impedance buffers,
which leaves me with the input summing problem.

Note...the electrical "star point" is not a physical point. In practice
the inputs/outputs are distributed along a common cable, of unspecified
length, which can change.

Comments appreciated, other than "design yer own f****** stuff", of course
:-) Just pointers to info would help.