Audio ground loop isolator

[0b01010011]

So I have a car that doesn't have bluetooth but does have an auxilliary input.  So just use a headphone to RCA cable and all will be fine....  well fine until you want to charge the phone from the car charger.  I don't know if it's particularly a problem with my model of car (Lancer CJ), but this causes a whine that goes higher and louder with the engine revs.

I recognised this as a ground loop issue but of course didn't want to spend money fixing it.  So I was looking at my collection of random boards, and found a PSU board from an old Sony BVM that had 2 common mode chokes, both identical.  Essentially they are just transformers and there were 2 identical ones.

So I hooked one to my signal generator and scope and the response is suprisingly flat from the low 10's of Hz up to at least 100kHz.

I wired them up to some connectors and tried it out and it works no problem!

[wraper]

Dunno if this is good solution for sound, you won't see distortions on the scope, unless they are like >5%. Although with crappy car speakers and road noise might be fine. I would isolate charging side, not audio.

[0b01010011]

Supply side isolation would be more of a possibility for just a bluetooth receiver such as this Sony 'knob' I am thinking of buying...

http://www.sony.com/electronics/in-car-receivers-players-accessories/rm-x7bt

I doubt this thing draws more than 50-100mA so one of those SIL package isolated DC-DC converters should work for this.  Might try that.  Much smaller than this solution anyway.

[tszaboo]

Isolating power is probably simpler than isolating audio. Just sayin.

[GreggD]

You can isolate audio with a 300-ohm modem transformer. Works fine connecting one pc audio to another pc.