Tír Na HiFi

Yes, I understand what you are saying and thank you for all the advice, now trying to turn that advice into action is the thing!

But does this not mean that, assuming everything stays connected to each other, it's "safe" to disconnecr the earth of one of the amps, as it will be connected to earth anyway via interconnect? The logic being that if there wasn't another ground connection being formed by the rest of the system, you'd never have the hum in the first place?

I'm thinking the same.....Obviously it's not as simple as that or is it?

out of curiosity on the preamp unplug it and test continuity between earth pin on the plug and rca out/in gnd?
(put the multimeter gnd lead on rca gnd)
id doubt using interconnect gnd as safety earth would pass legislation,
because theres a chance the interconnect gnd would blow like a fuse in the case of an electrical short before the trip switch or fuse would go

nige2000 wrote: ↑Tue Feb 20, 2018 10:41 pm out of curiosity on the preamp unplug it and test continuity between earth pin on the plug and rca out/in gnd?
(put the multimeter gnd lead on rca gnd)
id doubt using interconnect gnd as safety earth would pass legislation,
because theres a chance the interconnect gnd would blow like a fuse in the case of an electrical short before the trip switch or fuse would go

Yeah, there is continuity between preamp plug earth and rca ground.

But as I said originally with the preamp earth disconnected and one of the power amp earths disconnected absolutely no hum.

Should just mention that there are 2 glasses fuses on the power side of the amp and 2 glass fuses on the phono/loudspeaker connection side.

Are they there as a protection as well?

Yea the fuses are another line of protection

So if any two of the three amps are earthed you get hum?

The indirect diode or rectifier earth to gnd connection is the best way to do it

nige2000 wrote: ↑Tue Feb 20, 2018 11:22 pm Yea the fuses are another line of protection

So if any two of the three amps are earthed you get hum?

The indirect diode or rectifier earth to gnd connection is the best way to do it

Preamp not earthed
right OR left amplifier not earthed
NO HUM!

Preamp earthed
Right amp not earthed
Hum in left channel

Preamp earthed
Left amp not earthed
Hum in right channel

nige2000 wrote: ↑Tue Feb 20, 2018 11:22 pm Yea the fuses are another line of protection

So if any two of the three amps are earthed you get hum?

The indirect diode or rectifier earth to gnd connection is the best way to do it

Preamp not earthed
right OR left amplifier not earthed
NO HUM!

Preamp earthed
Right amp not earthed
Hum in left channel

Preamp earthed
Left amp not earthed
Hum in right channel

That's pretty much any two

Don't see any other worthwhile options
Best of luck with it

nige2000 wrote: ↑Wed Feb 21, 2018 12:00 am That's pretty much any two

Don't see any other worthwhile options
Best of luck with it

Thanks, it won't be from the want of trying on your part.

Will see what I can do or get done with your suggestions.