Automatic Audio selector device

[SinclairZX]

Hello,
Does anyone know of a way (or a prebuilt device) that will allow me to have 2 audio input devices and 1 output with an automatic switch between the two. For example:
On Input 1 i have a radio which is the default throughput
On Input 2 i have a microphone - when the microphone provides output the switch automatically selects Input 2 as the throughput - then diverts to Input 1 when switched off.
Hope that makes sense.. Thanks

[tomd]

The simpliest way (i think) would be to have a 'push to talk' button when you want to use the microphone, though I suppose it could be done electronically and there might even be devices on the market.

[booksworth]

It can be done, at a price! Canford Audio sell professional kit for this sort of thing, costing �100 to �200, and you would have to fit the bits into a box along with a power supply for yourself. Not for the amateur. - - - - It may be that Maplin do something cheaper. What you are after might be called a "gated" amplifier, or a "voice-over" unit.