Yes, we usually design an amp with input ground floated by a 10 ohm resistor from the power supply ground.
But Quad 405 amp is a little bit different, the input op-amp also function as a DC servo control circuit, if it connected as original Quad 405 ground wiring, it will control a nearly 0v dc output, but if the input floated, it will has a small DC voltage output, both ground connection have no different in sounding, but for the 0v dc output, Quad 405 user better connected the DIN input ground to chassis.
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Currently I'm using a pulled pair of 10k uF, 63V Rubycon caps.
I had initially fitted a pair of these : KEMET ALT22A153DE063 Electrolytic Capacitor, Long Life, 15000 µF, 63 V, ALT22 Series, 26000 hours @ 85°C, ± 20%. I put them in the original clamps and silicone.
I swapped back to these which explains the messy fit and single screws on the clamps. It was a bit easier to work on with these smaller caps. I even tried the best of the original caps which I used very tentatively. As expected the problem didn't change at all.
I will tidy up the wires once I get the new caps in. I have bought some screened coaxial cable to rewire the input wires. Hopefully that might get rid of the left channel hum.
Regards,
kffern
