An amplifier hum issue

[Milo66]

Hi,
Ive just put together an amp / preamp combo. Every thing sounds great but it has an audible hum when the amps input cables are connected to the preamps outs, the hum is not effected with the volume, its a set volume.
The weird thing is if i connect either the left or right channel only via the cable theres no hum?
Its only when both channels are connected.
Anyone got any ideas?
Regards
Mike

 

[Mooly]

This is a common scenario and invariably caused by incorrect grounding arrangements.

If you apply shorting links to both power amp inputs does it still hum? Have nothing else connected at all apart from speakers.

If it does still hum then you have problems with the grounding of the power amp.

 

[U130421]

Look here about such problem.
http://hifisonix.com/wordpress/wp-content/uploads/2019/02/Ground-Loops.pdf

 

[Bonsai]

This is also excellent

http://hifisonix.com/wordpress/wp-c...4/ilimzns-Excellent-Posts-on-Ground-Loops.pdf

 

[Milo66]

Thanks for all your info , as im new to this its a great help.
I think i found a few errors,
The mains enter the amp in between the inputs is one of them.
Will let you know how i get on

Thanks again
Mike