Audio signal sensing auto on/off switch

Sure this box can use 12DV trigger, not just a digital input?

Yes, I can confirm that this box can be controlled with 12VDC. I have one, what you need to do is connect the green plug to the 12V trigger output.

Sure this box can use 12DV trigger, not just a digital input? 

Good idea (to use the existing 'load sensing' power strip to control a heavy duty power relay (assuming that the big amp will melt the strip/contacts). 

I've never seen  a source with a trigger in that price range. And who would want a one source system?

@fuzztone 

I meant the source to provide audio signal to the subwoofer amp(s), it can be a integrated amp, receiver or pre/pro.

Is that 12V linked to 'power on/off' of the receiver?

@kraftwerkturbo 

The 12V trigger output will be OFF if the receiver @ standby, it will turn on went the receiver power up.

BTW, if you choose not to diy, the relay controlled outlet box that I suggested on the first post can be controlled by Universal control voltage 3-60VDC or 12-120VAC, or connect directly to a 12VDC trigger, or even 120VAC.

On one receiver, I have a 12V trigger. Is that 12V linked to ’power on/off’ of the receiver? How many mA can those 12V triggers typically produce (to directly control a relay)?

Receiver 12V trigger output usually can provide up to 50-100mA. If you want to directly control a relay, my suggestion is utilize solid state relay since its input is optocouplered and only require a few mA to activate. To control 1500W power amplifier, choose a SSR can handle 40A or higher.

Solid State Relay

Will now try if the big phat 1500W power amp can be controlled (I assume it has a ’softstart’ to not smoke that power strip right a way.

If your ’fancy’ power strip ’controlled’ outlets can’t handle the load of 1500W amplifier for long run, I suggest diy a box with 120V power relay/contactor controlled outlet plug into the power strip.

120V Power Relay

AC-AC SSR

I forgot that I had a 'fancy' power strip here (bought and forgot). Now looking at it, it has a 'main' and some 'controlled' outlets. When the 'main' draws power (turned on), the 'controlled' outlets are turned on as well. Works in the test setup (receiver is 'main', CD player, tuner, another receiver, Schiit Modi 3, etc) are 'controlled'. 

Will now try if the big phat 1500W power amp can be controlled (I assume it has a 'softstart' to not smoke that power strip right a way. 

On one receiver, I have a 12V trigger. Is that 12V linked to 'power on/off' of the receiver? How many mA can those 12V triggers typically produce (to directly control a relay)?

The Tricklestar strip is an excellent suggestion, it's a current sensing device. 

If you're looking for a ready to use 'box' audio signal sensing switch, check out the RDL ST-ACR1

What part of no 12v is so incomprehensible?  I've never seen  a source with a trigger in that price range. And who would want a one source system?

A Tricklestar strip will work. In my experience they are transparent.

If the sources have 12V trigger output, you can use a relay controlled outlet for your subwoofer amp.

https://www.adafruit.com/product/2935?gclid=EAIaIQobChMI8Zmxyvum_AIVgBXUAR1UAAuGEAQYAiABEgJM7vD_BwE