andrewb
Well-known member
Someone asked me for pics of how I added a sub output to one of my AR's, so I' figured I'd post a thread instead of emailing the pics. Note I did this a long time ago and it's a bit hacky, but it works.
The basic idea is based on this tutorial for converting a speaker-level output signal to a line level output:
And since websites all disappear, here's a pic of the basic idea. We want to tap off of one side of the AR's audio signal, step the voltage down using a resistor divider, and then output that to an RCA cable, that can connect to the input of a subwoofer:
And here are pics of how I did it. All you need are the two resistors, and an old RCA cable that you can cut in half. It can basically be any audio or video RCA cable. The center conductor of the cable is the signal, and the shield is ground. The center conductor is soldered to the midpoint between two resistors that reduce the amplitude of the signal. The shield is soldered to one of the ground pins on the 4-pin speaker connector (as you can see there are two pins that are connected to ground on the solder side of the board, and in the second pic below the shield is soldered to one of them.) The other two pins are the AUDIO+ and AUDIO- speaker output signals. Note that AR's are not stereo, but rather are a single audio channel, driven by a push-pull amplifier (so the AUDIO- signal is the inverse of the AUDIO+ signal, and together they drive the speaker).
It technically doesn't matter which signal pin and ground pin you use, as either will work the same.
I also drilled two holes in the edge of the AR (which I would never do now, that's hacky AF), and added a zip tie to mechanically support the cable, and prevent it from ripping off the resistors. Today I'd just use some Kapton tape instead.
The basic idea is based on this tutorial for converting a speaker-level output signal to a line level output:
Speaker signal to line level
Circuit to convert speaker signals for line level audio inputs.
www.epanorama.net
And since websites all disappear, here's a pic of the basic idea. We want to tap off of one side of the AR's audio signal, step the voltage down using a resistor divider, and then output that to an RCA cable, that can connect to the input of a subwoofer:
And here are pics of how I did it. All you need are the two resistors, and an old RCA cable that you can cut in half. It can basically be any audio or video RCA cable. The center conductor of the cable is the signal, and the shield is ground. The center conductor is soldered to the midpoint between two resistors that reduce the amplitude of the signal. The shield is soldered to one of the ground pins on the 4-pin speaker connector (as you can see there are two pins that are connected to ground on the solder side of the board, and in the second pic below the shield is soldered to one of them.) The other two pins are the AUDIO+ and AUDIO- speaker output signals. Note that AR's are not stereo, but rather are a single audio channel, driven by a push-pull amplifier (so the AUDIO- signal is the inverse of the AUDIO+ signal, and together they drive the speaker).
It technically doesn't matter which signal pin and ground pin you use, as either will work the same.
I also drilled two holes in the edge of the AR (which I would never do now, that's hacky AF), and added a zip tie to mechanically support the cable, and prevent it from ripping off the resistors. Today I'd just use some Kapton tape instead.
