"Ian Iveson" wrote in message
...
Norman Billingham wrote:

I have a pair of ATC SCA50 active speakers. They make a great sound but
the amplifiers run all the time, even when there's no signal to amplify.
Since they run in class A there is a significant current draw 24/7. As
they are at opposite sides of the room, turning them off involves two
switches and doesn't get done unless we're going away.

My previous Bowers Active 1s had an audio signal sensor in each speaker
so they went onto standby mode if there was no audio and "woke up" when
audio was present. Given the cost of running the ATCs all the time I'd
like to do the same with them.

There obviously needs to be a "switch off" delay so that the speakers
don't power down in quiet passages.

Do any of you experts know if something like the Velleman 4700 would do
the job? Or of any other circuit? I'm perfectly happy assembling
something but I'm no circuit designer.

Thanks in advance.

Do you turn the rest of your audio system off, or does it go into standby?
Jim or Chris have suggested clear solutions if you habitually switch
another part of the system off.

If the rest of your system is left on standby, and you are into a bit of
assembly, it should be possible to tie a mains switch for the speakers to
the standby function somehow. Possibly easiest would be to use the standby
indicator light to trigger a simple logic circuit, and take a strong
low-voltage signal from there to a 5V mains relay or SCR in each speaker.
If this results in power-up or -down thumps or whatever, things could end
up a bit more complicated.

A switch that would sense an audio signal and make a decision would
require a "watchdog" timer. Every time it senses a signal it would reset
itself, otherwise it would time out and shut down the system. Not
particularly hard to do, although preventing it from interacting with the
audio signal in a bad way may be a bit tricky, considering you would need
it to interact...

If it were dead easy, the speaker makers would have done it I suppose.

Ian

not an expert



Thanks to everyone for some useful suggestions. I think I'll look into the
Maplins remote switching power units first though it will be yet another
remote on the coffee table!

I guess I coudl access the circuit diagrams for the old Bowers units and
copy those but that's a more complex path.

Anyway - thanks again to all