Auto Power-On Audio Amp

[iceblue]

I'm busy building an active subwoofer which I would like to automatically power itself on when the source is powered on. I need suggestions on how to do this.

I do not want a remote trigger wire so want to get it to power on via signals recieved at the audio input.

Quick description of my plans:
I am building a home audio system. The source will connect to the a receiver which I am building. The reciever will amplify the signal for the speakers but not the subwoofer. I want the subwoofer to power on when ever the reciever is on.

Currently I am thinking of injecting a high frequency signal (say 35KHz) into the LF audio signal which will be sent to the sub. I would then filter this out at the sub using a passive BPF and use that signal to power on the subwoofer amp. If the receiver is off, the 35KHz signal will not be present and the sub will power off.

Ok, so does this sound like a good idea or is there a better approach?

 

[MRCecil]

Have you searched for a "wake up" circuit that would work for your design? One should be able to energize the amp with just the audio signal as the "on" trigger and an off delay of the proper timing to fit your needs.

 

[iceblue]

That was something I considered, but the problem with that is suppose I am watching a movie with long periods of speech or even silence, followed by a sudden explosion. The amp may have switched off already during the silence and not be able to switch on fast enough to reproduce the entire sound segment. Or do you think there would be sufficient low frequency audio present throughout a movie to keep the system active?