More Mute Line Fun

My empeg-through-headunit-with-speakerphone install had been working great around town. I headed from DC to Pittsburgh and back over the holiday and began having problems.

The amusing version: after about 2 hours of driving, rolling up my window all the way would cause the stereo to mute for a moment, then unmute. Then, rolling it down all the way would do the same. Then, about 20 minutes later, braking caused the same behavior. Pretty soon, it was muting on turn signals, acceleration, whatever. Finally, it just stayed on mute.

Removing the empeg (which wasn't muting, except when the speakerphone system requested it, of course) fixed the problem with the stereo. I reverted to CDs for the rest of the trip.

I suspect the problem is that both the empeg and headunit are wired to the speakerphone's (a parrot CK3000) mute line in parallel. The potential at the sense input of the empeg vs. the sense input of the headunit aren't the same, and therefore a current running from the headunit into the empeg, when installed, that causes the headunit to be close to or at the transition point it recognizes as close to "ground" than "+12". As the unit heats up, it gets pushed over the line.

I'd like recommendations on a solution. Would a couple of diodes, each between the headunit and empeg and the common connection to the mute line fix the problem? If so, can someone with experience recommend a type/specification?

Thanks again and again...
-brendan

That's possible. Or it could be a battery or voltage regulator problem in the car. Or even a loose connection somewhere.

I did a bunch of jiggling of wires with the empeg out (you can reach through the sleeve) which seemed to make no difference. Put the empeg in, the headunit's phantom mute sensitivity is high, take the empeg out, headunit only mutes when the speakerphone tells it to. Doesn't seem like a loose connection. Could be voltage regulation as well, but even if so, that seems more like a trigger than the real "problem" of current leaking into the empeg mute sense line.

I'm going to pick up a couple of 1N4001s from the shack tonight and schedule some surgery for later this week.

Thanks Tony,
-brendan