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Automatically turn on a subwoofer that lacks 12V trigger input?


May 21, 2024
I'm thinking of buying KEF KC62 for living room. The only concerning issue is that auto-standby of KC62 does not work reliably at low volume.
I contacted KEF support, they told me that the feature could be turned off on the latest firmware. I could send KC62 to their service center for updating firmware if I get one with older firmware. Not sure if auto standby is still broken on the latest firmware.

KC92 reportedly has fixed the issue, it also has a trigger input, but much more expensive than KC62. At least in Japan.

My AVR (Denon AVR-X3800H) has a trigger output. Can I somehow convert 12V trigger output of the AVR to USB, so that I can connect to USB-controlled power strips and turn on the sub automatically?

There are other solutions though. I'm just curious if I can add a trigger input to the subwoofer in a way I've shown above.
If this works seems like a most elegant solution to the problem.

* Use AVR's USB port and USB-controlled power strip directly at the cost of USB stick playback. I don't use USB sticks for playing music for now.
* Use a power strip that monitors power draws from AVR and auto turn on the sub. (Does this work reliably?)

Power strip. Originally Meant for turning on devices when a computer is turned on. Works by detecting power draw on USB input.
DC to DC converter which converts DC 12V to USB (DC 5V)
Terminal Adapter, so that I can connect the cable above only with a screwdriver, not with a soldering iron.
Some 3.5mm mono cable for 12V trigger

AVR 12V trigger output -> trigger cable -> terminal adapter -> DC12V to USB (DC 5V) converter > USB controlled power strip -> subwoofer power cord -> subwoofer
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I would use a master slave power strip.

It's very straightforward: Once there is current drawn from the master outlet, all slave outlets are switched on.

Once current drawn from the master outlet drops below a certain threshold, all slave outlets are switched off.
I use theseTrickleStar. I find them reliable. It’s possible to adjust sensitivity some, because if the control device draws a low current when on, it might not be enough to trip the switch. Conversely, if the control device draws a high idle current, the other devices might not switch off. My projector is the control device, and the AVR and sub are the switched devices. I can use the projector remote to turn the whole system on or off, which is easy for my wife. But for myself, I set up Home Assistant on a Raspberry Pi, and can control Projector, AVR, Blu-ray disc player, and AppleTV all from an iPad, no remote required for those. Still gotta use the remote for the cable box, since no CEC or IP available, but an IR controller on the Home Assistant will fix that. Future project.
Trickle Star has other models that can switch on or off by sensing activity on a remote control and/or motion activity in the room. I am happy with what I have, so never tried those.
The Adafruit device looks unique and pretty flexible. Interesting.
Thank you for the answers. Unfortunately I can't find a power strip that has a trigger input locally.

I will try a master slave power strip first, some of such products from Japanese manufacturers allow adjusting sensitivity.
Many of the Panamax multi-bank power conditioners feature a 12V trigger input to control energizing of one bank. You can pick up a used 5100-EX in good shape on eBay for less than a hundred bucks.
wifi outlet plugs. Can control with a smart phone, alexa, etc.
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