>> My original design had the PIC ground and the analog ground connected
>> together.  THEN I read the specification for the player and it says
>> "Analog return - Signal, never to be grounded inside attached device."
>> I do not have access to the internals of the device
>
>Are you going to power your circuit from the same power source as the MP3
>player? Can't you open it and take a peek? Mostly the analog section is not
>that complex. This phrase doesn't necessarily mean that you can't connect
>the two grounds, if I understand it correctly (without its context).

You will probably find the analogue ground is at half the digital rail
voltage. I have some analogue FPGA devices where they do exactly that.

>Can you at least look at the output with a scope -- referenced to the MP3
>output ground? A capacitor (to block any DC) and two resistors (to bias the
>AC at half the supply voltage) may be all you need.

This may well be all that is needed - some way of blocking the DC
connection. certainly worth a try, and if it does not work well, then you
have the fallback position of a differential amplifier.

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