speaker output to line level in car

Sensors Sound & Audio
1

I’ve got a project going using the NR-52 as a handsfree and music streaming in my car. Some problems with this that I can see:

  • the NR-52 outputs speaker +/- (which I believe is a differential audio signal?), but input to head unit is single-ended

  • the input to the head unit uses an Audio GND, isolated from bus & chassis ground lines

  • impedance mismatch of course

From my research, some solutions might be:

  • audio transformer for isolating the circuit from the audio lines

  • differential amplifier to convert the +/- to a single-ended signal

  • some combo of the above (differential isolation amplifier?)

Any of that on the right track? It’s bluetooth, so don’t need premium sound quality, but I don’t also want to have a sub-par signal. I should in theory be isolating the bus signal too, since it’s got it’s own GND separate from chassis as well…

Any recommendations? Order of isolation vs single-ended conversion? Any off-the-shelf solutions? Or is this all wrong?

fwiw, CD changer that I’m emulating output 850mV into 10kOhm (I think I’m reading that correctly…needs more research there too).

2

The outputs and inputs on this board are differential, connecting the (-) output to ground might cause issues. A audio transformer would work but you’d need to figure out what impedance the blurtooth board has and use a transformer that’s a match.

Another thing you could use is an OP-amp, that would convert things to single ended.