Phantom power in power amp

[diesel engine]

I am planing a PA system for a school building. my design is individual powered speakers(18 total) and a central preamp and splitter. I am thinking about a phantom power through signal cable to switch on a relay to control amp power supply. is this approach feasible? any thoughts?

 

[kanwar]

Have you thought about sending DC voltage mixed with the signal? But it has to be a balanced line and AC coupling is needed for the at the input end along with DC sensing circuitry.

 

[omishra]

Post deleted..not relevant.

 

[Fantastic]

I am planing a PA system for a school building. my design is individual powered speakers(18 total) and a central preamp and splitter. I am thinking about a phantom power through signal cable to switch on a relay to control amp power supply. is this approach feasible? any thoughts?

Sounds feasible. You don't need any power for the turn on signal. Possibly much less than a mA. The other end could be buffered and triggering a relay. Many systems use 12 V dc typically. Use some reasonable sized series resistor at the control (pre) amp like say 10 Kohms or more in series with the signal lines so that any short at the other end will not matter. In any case this would be required to prevent an ac short through the dc supply used to switch. Needless to say that the dc used to switch should be very clean ( well filtered and regulated). Any hum on it will appear in your power amp.