Hum from amplifier

Numpty112233

When I have my AV receiver pre out connected to my stereo amp HT bypass I get a constant slight hum, regardless of stereo input or volume.
Is this a ground loop hum?
What can I do to fix it?
AV Receiver is Yamaha 3070
Amp is Denon PMA-2500NE (HT bypass is unusual in that it goes straight into the power amp section completely bypassing preamp)
It requires both L & R cables removed to stop

dobrykamil

Maybe this will help?

gibbsy

It does sound like a ground loop, somehow manifesting between the receiver and the amp. Do you have any mains cables running alongside or near to the cable? Are the sockets on the same block or different mains socket. If so try putting both power sockets into the same plug or extension. Sometimes the simplest solution is best.

dannnielll

When I read these I am tempted to suggest changing ones socks.  But actually that is a classic example of a ground loop. How to sort it. ?. I suppose using an optical link is impossible?. Other possibilities are that the amplifier and receiver are on different power sockets Ideally they should share tge exact same socket . If not  so , removing the earth connection from one or the other can cure it,if the earth is being carried by the braid in the rca cables.
Now you say  receiver not tuner, so if the loudspeaker are connected to it is there hum?. If there is in the absence of the  Àmplifier, then it is not  mains hum, but a worsening problem in the power supply of the reciever.
But assuming mains hum, rearranging the cables so that the area   within the loop is minimised. That means .. counter to common sense   making the power cables to both amplifier and receiver be parallel to each other and very close. Likewise the two RCA leads ,and all 4 cables very close together.

Numpty112233

I have 4 double sockets on their own ring main.
The stereo amp was in double socket 1 and the AV in double socket 4
The hum continued when the AV receiver was unplugged but the Bluray player was left on and vice versa.
Moving the AV receiver plug to double socket 1 made no difference. Still hum.
Mains loop cable is kept away from all other cables however component mains power cables are near it

Hixs

I had this. After trying for weeks to find a solution I ended up buying a Beresford speaker switch and ditching the bypass.

BTW HT bypass always skips the preamp section. Your AVR becomes the pre amp. Your amp just provides power.

Numpty112233

Optical link no possible
same socket doesn't resolve (particularly as Bluray into AV keeps the hum going)
There is no hum when just the av receiver is on and not the amp
There is no hum when the amp is on and both the RCA leads from the AV receiver are disconnected
Power leads are vertical and separate by over 1m and RCA horizontal, photo's attached, so not easy to run next to one another

Numpty112233

Did you try anything like post 2 suggests?

Hixs

Yeah none of it worked. The hum was lessened to a degree, but it persisted.

Numpty112233

Have just tried putting amp, receiver and Blu-ray all into an extension lead into 1 socket
Still hum - no cure
Not sure if it's relevant but AV receiver has metal earth pin on plug, stereo and bluray have plastic pins so presumably not earthed?