Interesting hum in 881 receiver

I picked up an 881 yesterday that is in very nice shape overall. It was humming noticeably when I auditioned it. I know that's a common issue with these and I have read many of the posts on AK and elsewhere about fixing the hum. I'll do the re-grounding things that some people have had success with.

I'm posting here because the nature of the hum is interesting, at least to me. When I checked the 881 with test speakers before I bought it, there was hum at any volume and on all inputs. That says power supply and/or power amp issues to me.

Yet when I got it home and listened to it with headphones, there was virtually no hum and it sounded great. Huh? So I connected my Minimus 7 test speakers and the hum came back. Speakers connected and selected = hum. No speakers connected = no hum. Hmmmm... (Or hummm...) :screwy:

I think I'll first try the ground improvements that have worked for others. If that solves the problem, I'm done. If not, I'll get the scope out and see what's going on. When I get around to it, of course.

Fouled speaker selector switches or speaker relays?

ODD the headphone is post relay pre speaker switch.. and there is a 330 series dropping resistor for the HP, so the HUM may be the PS loosing regulation under load...

Mine was only humming physically (the transformer) not in the speakers.

I reflowed all solders on the power supply and driver boards and the hum gone.

Maybe the mute circuit and / or switches?

Pls Let us know the results

Most probable cause power supply , caps, diodes, etc.
As vigman said the hp output is at the power stage with a resistor in series.
Check the ps caps, First.

Hi everyone. Thanks for your suggestions. I'm a big believer that most problems come from a simple source and have a simple solution. This 881 is in great shape so I started troubleshooting with a cleanup and checkout of all connections. I pulled off and reseated all of the connectors on the boards and then tightened the grounding screws. After power-up, no more hum! That was easy... :thmbsp:

This 881 sounds and looks great. The tuner sounds really nice. I have a pretty fancy set of Mac tuner, preamp, and power amp components sitting next to the 881 right now. The quality of the design and construction of the 881 is nearly in the same league as the Mac stuff to my semi-professional eyes. No, I haven't had a chance to really compare how they sound and my tinnitus-plagued ears wouldn't pick up the subtleties, perhaps. The 881 is going on loan to a friend tomorrow to see if she likes it better than the Yamaha CT-810 integrated and CT-800 tuner I've lent her so far. I'm betting she prefers the 881.

Thanks again for the help.

I would love to get a 881. I love my 661,771. They sound great!

Make sure you clean the connector on the Driver Board (F-1499A) - pull that card out, clean both sides of the connectors well.

For my 771 that was the principle source of the hum.

peterfranks said:

Make sure you clean the connector on the Driver Board (F-1499A) - pull that card out, clean both sides of the connectors well.

Click to expand...

Yep, I did that when I went through the unit. That may have been some (or all) of the problem. Thanks.