> though I don't know how it works. It's called a "12v trigger." THX introduced the trigger port to allow one amp to start other amps. Before that amps would h

> though I don't know how it works. It's called a "12v trigger." THX introduced the trigger port to allow one amp to start other amps. Before that amps would have a 110V passthrough socket. THX trigger is a mono 1/8th inch / 3.5mm TS plug. Each device usually has one 12V in and a 12V out. While it's on, it'll output 12V at up to 30mA[1]. Due to current fluctuation and the low max amp it's recommended to use an opto-electronic isolator at the input. THX originally introduced it to allow for home cinema surround. At the time commercially available amps only supported 2 channels, so the first THX systems had one receiver decoding the dolby signal, providing a line level output that you'd connect to multiple stereo amps. Due to the currents required the 110V passthrough wasn't an option, so 12V trigger was born. Before 12V trigger existed the IR/Remote port, which allowed you to connect an external IR receiver to TVs, VHS recorders and Amps. This used the same plug, but would modulate the IR remote signal directly. You could also use this to connect multiple devices and allow them to send remote control codes to one another. But that feature disappeared quickly due to limited compatibility. In computers 12V trigger and remote ports inspired the I²C based DDC standard for VGA monitors, which allowed turning them on or off or changing settings. DVI and DisplayPort kept DDC as is, while HDMI expanded DDC into the CEC standard, which also allows controlling volume or sending media controls in a standardized way. Nowadays 12V trigger is mostly being replaced by HDMI CEC. ________________________ 1. Some devices support up to 80mA, Sonos even provides 100mA