audiolover,
Hopefully the responses posted on this thread answered your questions in your original posted message.
Just a guess you will continue to use the ground cheater on the sub amp because it eliminates the ground loop hum. You are not the first to experience a ground loop hum problem with a subwoofer amp, that uses a 3 wire cord and plug, and you won’t be the last.
Jensen transformer does make an isolator you could install between the preamp and the sub woofer amp that should/will break the ground loop circuit, thus eliminating the ground loop hum. If you are worried about it degrading the SQ of the sub I doubt with the Jensen isolator you would hear any difference.
http://www.jensen-transformers.com/product/sub-1rr/
I would recommend the Jensen transformer isolator over the ground cheater. But if you must use the ground cheater a GFI receptacle in place of your existing wall duplex receptacle would be a safer option.
You could add a level of personal protection from any risk of a life threating electrical shock by changing out the existing wall duplex receptacle outlet to a GFI. A GFI receptacle does not need an equipment ground to function/operate as designed. Just buy a good GFI duplex receptacle outlet, not one of those really cheap ones. I have seen the cheap ones fail and not trip open when called upon. Leviton makes a pretty good GFI duplex receptacle.
If you do decide to change out the existing duplex receptacle to a GFI replace the old one with a GFI of the same ampere rating. So if the existing is a 15 amp, more than likely the branch circuit is a 15 amp, you must use a 15 amp rated GFI duplex receptacle. You cannot install a 20 amp receptacle on a 15 amp branch circuit. A 20 amp receptacle can only be installed on a 20 amp branch circuit.
You can install two or more 15 amp receptacles, (a duplex is two), On a 20 amp circuit though.
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