I'd like to wire the amp to trigger on either the remote-amp output of the headunit *or* the mute line of the speakerphone unit.

Should be solveable with a couple of diode and/or possibly a relay...

First off: does the remote-amp line from a headunit or empeg trigger by providing +12V or by grounding? I presume +12V, similar to the "ignition" wire into a headunit. If so, it gets complicated.

Correct. It provides +12V when active.

The speakerphone itself triggers mute by asserting ground (or 0V) on the mute sense. So, I figure I need to get funky with some relays in order to have either line do the work.

Recommendations? This is what I have so far:

I figure at a minimum: 2 bosch relays, one wired "normally" on the remote line (+=remote, -=ground), one wired "reverse" on the mute line (+ side ignition, - side mute), with the output side of both wired +=ignition,-=remote-amp-sense and in parallel.

I don't know how many of these paths would also require a current limiting resistor and if so, what specification. For example, would I need to put a resistor in the output path, or do amps typically have a high resistance/impedance on their remote-amp-sense input? Would I need to put a resistor on any of the input paths as well?


Unless you're running lots of gadgets off the remote wire (in which case you should already have a relay in place and would have known that it provides +12V to tell the amp to turn on) I'd do it like this:

1 standard bosch relay (SPST)
2 diodes, 1N400x

Run +12V (fused, 2-5A, could borrow for instance from the amps +12V wire) to pins 30 and 85 on the relay, run the phone kit mute wire to pin 86.

From pin 87 run a wire with a diode inline (positive, (anode) end towards the relay pin 87).
This makes the phone kit also provide a +12V signal instead of a ground,
Add the other diode the same way to the remote wire from the empeg (positive, (anode) end towards the empeg).

Then tie the negative ends (kathodes, striped end) of the diodes together and to the amps remote turn on port. This makes a logical OR function of the two inputs. The amp will see +12V when either of, or both, the phone kit and empeg are active.

No current limiting resistors required - all the items are designed to run off/handle +12V without problems. When tapping into a +12V source with a failry small wire, put a fuse close to the point where you take +12V, this is to protect the wire from overheating (and in the end the car from going up in flames should the overheated wire set anything on fire) should it short out to ground.

If you intend to run lots of gadgets controlled by the remote, instead wire the diode to pin 85 of a second bosch relay, ground pin 86, run a fused +12V wire (fuse size depending on what stuff you're running) to pin 30 and hook your amps remote + your other gear up to pin 87

Edit: Oh yeah, if you're running out of space behind the dash, put the relay(s) and diodes (the latter should effectively take no extra space as you can run them inline in the wire (cut wire, solder in diode and cover with heatshrink tubing)) by the amp (assuming you having stuffed that into the dash as well...)

/Michael