Can anyone explain the Quad 405 internal grounding?

On all, the 'power' ground is via the heatsink to chassis.

On the DIN input ones, the 'signal' is grounded to chassis at the DIN
socket.

With the board removed, there is 10 ohms between signal to power ground -
as expected due to R2.

On late 405-2 with phono connectors, the phonos are isolated from the
chassis. Yet still shows that 10 ohm resistance between signal and power
ground.

On the early amp with nothing connected, DC at the output is about 2 mV.
On the phono version, 25 or so.

I'm guessing it's to do with early amps not having a mains ground when
connected to a Quad pre-amp, but later ones are.

Still seems weird to me.

--
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Dave Plowman London SW
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