Hi,

I'm looking for a device that will automatically switch 2 line-level audio
signals to a single output.

One of the audio lines (A) will always have a signal. This is the default
audio.
The other signal (B) will switch on and off. When B comes on, I want it to
become the active source, for as long as it is on. When B switches off, A
should become active again.

I found a device that does this for amplified signals
(http://www.cbav.com/Merchant2/mercha...ry_Code =SI-2)
but the price ($120) is pretty steep.

Does anyone know of a cheaper device to do this, or a circuit/directions to
build such a switch?

Thanks,
JohanE