schematic wanted for balanced/unbalanced mics and line ins

[John Asbacher]

I think I've looked in many places on the net but couldn't find a
circuit that will allow me to connect 'balanced' Line inputs and Mic
inputs, user selectable or pot. controlled to the line ins on consumer
cameras and Mini Disc Recorders. I'm not sure if transformers or op
amps are used in this situation.

[Kevin J. Shuholm]

I'm not sure exactley what your question is. Are you just trying to build a
mic/line preamp where the selection is done either by a jumper or by adjusting
a pot, and you wish to drive the line in on a camera?

If that is what you are doing, then you may want to check Walt Jung's book
"Audio IC Op-Amp Applications", published by Same and Co. There are circuits
for mic and line level amps.

For this circuit you could use the classic insrumentation amp, where each leg
of the signal goes through a voltage follower type buffer, and then feeds a
balanced to single-ended stage. By using a feedback R on each of the
followers, you can then connect the inverting nodes through either a pot, or a
jumper-selectable resistor to change the gain of the whole circuit.

Kevin

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Kevin Shuholm "It's still me and my machine for
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