I'm assuming these were opto-isolators?
I used
this. I admit to having no idea if that was a good idea or not. I just used the black connectors. I was unclear about which direction to hook it up, so I tried both ways.
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If the ground loop isolator has a spec for frequency response, it may roll off into the lower Hz range. It may also have an insertion loss dB spec, perhaps even a frequency chart.
I didn't think about frequency range of the isolator, I'll admit. And the Amazon listing doesn't mention it...and it didn't come with any documentation.
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This...is very frustrating...
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From one of the Amazon reviews;
the product eliminated the bass
Unless the isolator has a battery inside (thereby allowing a powered onto-isolator circuit) I am going to guess it contains a pair of tiny audio transformers. Low frequency (bass) signals generally require a more expensive (and generally larger/heavier) audio transformer, which I suspect the inexpensive isolator does not contain.
A better quality audio transformer based isolator
might provide decent bass signal pass through
and eliminate most/all of the annoying noise.
It can indeed be frustrating. Audio system engineers often learn some things the hard way, fighting with intractable problems that
shouldn’t be happening, but nonetheless, are.