If you have control over both ends and the middle of the system, you can probably design around the need for the isolation OR it’s understood to be incorporated from the start. When I use use the Motorola radio with the Motorola speaker and Moto wiring harness, no problem. But my brilliant idea of wiring the 2way radio to the vehicle’s factory AM/FM speakers breaks the radio since doing so grounds the audio output.
Suppose we take two telephone devices in a closed circuit intercom and set them up to talk to each other on the bench, fully compatible, but without isolation. Next, wire them up 2000 meters from each other and you’ll find that noise is naturally present but, worse, the grounds that are to be tied together are 2 volts apart. Wait, 3 volts. Now it’s zero. Back to 2 volts, wtf? (wobbly transfer function, hehe) Even though we can fully control the devices, the unpredictable path between them is causing noise and shifting earth grounds and problems. The isolation decouples the signal from the power. The noise will still be there but the fixed signal basis (audio here) can be used by the telephone pioneer to focus on amplification and signal processing.
Can I isolate the grounds with a diode? I’m not sure how to isolate them. The two are tied together on the sleeve on the TRRS connector. I may just throw a diode in from the amp negative to sleeve on the connector and see what happens.
A lot of electronics is getting things to talk to each other and never more literally than in the field of audio where there is a particularly diverse body of work. It’s solidly 100+ years old, there have been countless types and standards, each type and standard has countless products to get lost in (microphones, speakers, cables, vacuum tubes, DAC, storage media, connectors, wireless gadgets, effects), there’s infinity room for improvement. It took household name-level geniuses like Alexander Graham Bell and Thomas Edison to even begin to sort out what audiophiles today do for fun.
For OP, I’d check all the wires. I’m still suspicious there’s something in there.
Some test equipment is helpful and it doesn’t need to be lab-grade: a commercial audio mixer would be handy and could use a cooldown from your set at the club. So would a little probe ‘playing’ a tone or music that you can touch to various points and see what happens on the output with and without, for example, the proposed diode.
Thanks! Haven’t had a chance to fiddle much with the setup… It’s 100% a bridged amplifier after looking at the diagram. Cannot share a ground… Interesting thanks for sharing. An audio transformer might be enough to decouple the grounds so I could use a TRRS plug. I think but am not sure how to verify these little MAX amps are probably popular in cell phones? In which case they’d have some elegant way to decouple the grounds as well… but I don’t know how to lookup cell phone circuitry if any of that is open design.