McIntosh phone mute

[scottb721]

I decided to try an alternative method to muting the Mc automatically for phone calls.
Whilst I did use a phone car kit ISO mute cable, rather than having it open-circuit the car speakers I'm using it to disconnect the Accessories 12v(ACC) going to the Mc - the Yellow/Red wire on pin 10 of the Mc's 14 pin plug.
The beauty of the Mc is that it has a fade in/out feature built in which is a nice touch when killing or restoring power to it.

I already had a dedicated phone speaker fitted so I didn't worry about running any car speakers through the mute cable assembly.
Mute cable Assys generally have 4 sets of contacts for switching in the phone audio to the front speakers, and 2 sets of contacts for the rear speakers which simply go open circuit. I used one of the latter rear-speaker contacts since it's a basic on/off switch and also so I can expand later on to incorporate the car's front speakers should I choose to.

Here's a circuit I drew of my Nokia CA-160 mute cable and the Parrot version which I actually used in my car is very similar.
http://i.imgur.com/ZzOX9oT.jpg
Using the Nokia circuit as an example I would've fed the H/U 12ACC through either the Purple or Green wire. For the Parrot cable it's the Grey or Brown wire.


I used a mute cable as I had a couple sitting around but you could achieve the same result with a simple 12V that is energised by the MUTE wire from a car kit which goes to GND when the phone is in use.

Should I choose to use the front speakers for the phone audio I will simply run the front speaker wires from the amp through the mute cable. The Amp will be powered down when the Mc turns off so there shouldn't be any issues for the Amp.

PROBLEMS
As mentioned elsewhere I did find out afterwards that killing the Mc also turns off the Nav screen which is undesirable. My solution was to disconnect the nav plug from the Mc. Downside is voice guidance is no longer available however mine is set
to OFF anyway.