How would the cd4066 effectively isolate the audio signal?
I'm not following that either.. it's not an isolator... I think he's using it to eliminate switching noise with the digital pot...
that'll work with a cheasy mp3 player, nd a ipod, and a legit stereo system without the worry of connecting grounds and accidentally frying something (which I did : (, very expensive mistake, I blew my 700w amp in my car)
That shouldn't be a problem if you use the line-level input
to your 700W amp. Line-level signals (and loud headphone outputs) are in the ballpark of 1 Volt. 700W into 4 ohms is more than 50 Volts, and of course the voltage constantly varies with the music and the volume setting. For that kind of range (~1 - 50V), you'd need some sort of switch or pot for high-low sensitivity and some sort of protection for your low-voltage electronics. You are going to have the same high-voltage issue with the transformer... There is the potential for overloading it, and if it burns-out it could short and fry the amp.
I would guess
your 700W amp has a "bridged" or differential (push-pull) output where both speaker connections are "hot" and there is no speaker ground. If you ground the amp's ' - ' output, you'll fry it!
The MSGEQ or 328 should generally work grounded to the car chassis, with no ground to the amp's output. The only issue here is frying the MSGEQ or 328 with 700 Watts...
You can build a differential amplifier
with an op-amp. It would be "safe" for both the power amp and the differential amplifier, whether you ground one of the differential inputs or not, as long as you DON'T ground the power amps differential output
). But, you'd still need voltage dividers and possiblly some protection diodes to protect the op-amp from high voltages.