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AVR350 started humming

Dave Weystoner

Active Member
My 5 year old AVR350 has recently started humming through the speakers (there's also a mechanical hum from the unit itself, but I'm not so worried about that). My system compises the 350, DV137and B & W MT30 (5 x M1sats plus a PVI sub). A Sky HD box is also connected to the 350.

I thought it might be an earth loop, so I disconnected the 137 and Sky box from the mains (but not the signal cables to the 350); it made no difference. I have the 137 connected via analogue and digital. I have changed the ground lift switch position, with no discernable difference in hum volume.

I have recently changed the mounting of the front L and R M1's to the wall-mounts provided, so thoughty I may have introduced an earth problem; I have unplugged these and listened through headphones - the hum is still there.

The hum is just audible enough, through all speakers including the sub, to be annoying at normal listening levels and distance. It increases with gain, and jumps in volume at 79dB amd 85dB.

Does anyone have any idea what it is, and whether there are any other tests I can do to nail it down before I talk to Arcam?

Many thanks,

Dave
 

Mark.Yudkin

Distinguished Member
To see if it is a common Sky box ground loop, totally disconnect it from absolutely everything. If that help, reconnect it to the amp and power, but do not reconnect its signal feed. If that helps, experiment with the signal feed connection and report back with full details, including the specific socket types (sorry, don't know them from here).

If complete elimination of the Sky box does not help, also unplug the PVI subwoofer from the wall socket.
 

Dave Weystoner

Active Member
Thanks for your input Mark. I have tried your suggestions, in the sequence you advised, but I couldn't remove or reduce the hum. I don't have a spare amp to swap out, otherwise I would try that. I guess it's a call to Arcam.

Dave
 

Dave Weystoner

Active Member
Thanks yachadm, but the unit is just about to be returned from Arcam, and I'm just about to be £250 lighter. Worryingly, I'm told they couldn't replicate the hum, but have found lots of other problems. They have replaced the DSP board and a number of capacitors amongst other things, so I guess it's similar to the Condor Audio refurb, in intent if not perhaps in scale.

If I still have the hum when it's back in my system you will hear the AARRGH! all the way from Dorset.

Dave
 
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