Ground Loop Hum

[nige2000]

continuity between chassis and mains earth and star gnd?

[Cyndale]

Firstly star ground is the contact in the middle where all the red leads are meeting, yes?

Continuity...
Yes - between earth and star ground
Yes - between earth and chassis
Yes - between star ground and chassis

[nige2000]

right... star gnd is the center bolt

mains earth should be going to chassis
star gnd should be isolated from chassis
then continuity should be checked from input / speaker gnd and the chassis (this is to ensure there isnt another direct connection between mains earth and gnd)
then a wire should be brought from star gnd to the earth chassis connection point via back to back diodes

[Cyndale]

right... star gnd is the center bolt

mains earth should be going to chassis
star gnd should be isolated from chassis
then continuity should be checked from input / speaker gnd and the chassis (this is to ensure there isnt another direct connection between mains earth and gnd)
then a wire should be brought from star gnd to the earth chassis connection point via back to back diodes

Firstly, thanks for all the help...
1. Mains earth going is going to chassis - nothing to do there.
2. Star ground should be isolated from chassis - how?
3. Input/Speaker ground - meaning interconnect ground connection/speaker ground connection - check no direct connection between mains earth and ground.
4. Could you show a picture of a wire with back to back diodes or explain what kind of diodes exactly!

Mucho Apprecatio!

[nige2000]

Take the gnd 0v as your star ground
Un bolt that from the chassis
Maybe put a new bolt in that point wrap it in insulating tape or heat shrink to isolate it from case then check if there's still continuity between chassis and interconnect/speaker gnd
If not that's good
Then in diagram you'll see a bridge rectifier which is basically doubled up diodes back to back

Diodes have two leads and are directional join the dissimilar ends together one point goes to star ground other goes to earth
Or u can use bridge rectifier as in diagram

[nige2000]

Actually it looks like earth is connected to power gnd on the capacitors that has to be disconnected
I'd cut that connection and extend that earth wire to bolt it on were star gnd was then put my back to back diodes or bridge rectifier from the new star gnd point to the New chassis earth point

[Cyndale]

Thanks for all the information and such a positive response to my plight, a lot to digest and figure out!

[nige2000]

Well the way it is your signal gnd is going through the wall sockets

Maybe there's a service shop near you that can do the change if you dont feel confident

[Cyndale]

Well the way it is your signal gnd is going through the wall sockets

A very succinct way of describing the problem!

So with the earth disconnected from the preamp and one of the power amps, how does that break the earth loop!

[nige2000]

Well on your power amps at least your signal interconnect ground is directly connected to mains earth
The way it's behaving I'd reckon the preamp is the same
Which means there's multiple signal return paths creating the loop between the amps ( meaning through earth and through interconnects)
When there's only one amp directly earth grounded it is of no consequence as there's only one signal return path the interconnect

Ok?