IMHO a better why to "isolate" a preamp is through transformer coupling. Electrical isolation IMO is more important than mechanical isolation. Ground currents in your ICs will generate noise, it's Ohm's Law. Even balanced ICs can have issues. Typical differential inputs have a high CMRR (common mode rejection ratio); but that's assuming perfectly equal source impedences. They seldom are: typical soures can have 10-20ohm imbalances. This can lower the CMRR of the reciever (amp) by 20db or more. Transformers have very high CM impedences and can handle source imbalances very well. High CMRR means your ICs won't be picking up any noise. I know transformers get a bad rap from some audiophiles; but you'd be surprised at how quiet and good a well designed transformer coupled system can sound.
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