Super loud buzz from amp

[olds1959special]

I don’t know what’s up with my system. I spent hours trying to diagnose another problem. After re-connecting my pre after changing tubes, I got a super loud buzz coming from one of the amps that I thought was a cable, but then tested the cable and it worked, so I flipped the cables around and that fixed it. If I don’t touch anything it will probably work right. It sounded like a badly connected cable.

(Since my pre hums a tiny bit I’m tempted to have it looked at and have the capacitors possibly changed, but don’t want to go through this again if I start disconnecting and reconnecting things.)

 

[solderdude]

When swapping cables fixes it there is no need to have capacitors changed.

Clean cable contacts and amp contacts (where the cable goes into) and/or replace the cables.

 

[olds1959special]

When swapping cables fixes it there is no need to have capacitors changed.

Clean cable contacts and amp contacts (where the cable goes into) and/or replace the cables.

Sorry to confuse two issues. The hum from my pre is a separate issue.

 

[olds1959special]

What are you using for cables?

WBC 6 foot Mogami RCAs. I tested the cable that seemed to be the problem with a multimeter, no shorts, and listened to it another system and it was fine. Then another amp buzzed after moving cables around. Finally it started working normally.

 

[Blumlein 88]

WBC 6 foot Mogami RCAs. I tested the cable that seemed to be the problem with a multimeter, no shorts, and listened to it another system and it was fine. Then another amp buzzed after moving cables around. Finally it started working normally.

Maybe old solder joints in some of the RCA jacks?

 

[solderdude]

Looks like a poor contact... perhaps even in one of the connected devices. Wiggle the connectors to find out.

Hum from gear may not be the capacitors, it could be, could be ground loops as well.

 

[olds1959special]

Looks like a poor contact... perhaps even in one of the connected devices. Wiggle the connectors to find out.

Hum from gear may not be the capacitors, it could be, could be ground loops as well.

Hmm, the connections are reasonably tight. I was adjusting the cables ends with a tool to make sure they fit right. They are pretty snug now. I’m scared to try to wiggle anything now, but I could. Only one amp has a loose RCA connector in the back but doesn’t seem to be the source of any problem I can tell.


About the possible ground loop causing the light hum in pre:

How can I test/fix a ground loop relating to the pre? I have tried plugging into same power strip as the amps. Also tried flipping the 2 prong connector as per the recommendation of the previous owner, but that did nothing either.

Do I need to try something with a grounding cable?

 

[MaxwellsEq]

I got a super loud buzz coming from one of the amps that I thought was a cable, but then tested the cable and it worked, so I flipped the cables around and that fixed it. If I don’t touch anything it will probably work right. It sounded like a badly connected cable.

If it's really loud, but goes away after disconnecting and connecting everything, that could well be a connector (plug or socket) that temporarily lost its shield / ground connection. Sometimes it disappears when you touch the chassis because you are sufficiently close to "ground".

With RCAs (because the centre pin connects first) it's possible to cause this by not having the cable fully pushed in. For this reason, unplugging and plugging RCAs in is best done with everything turned off. However, if you are confident that everything is tightly connected, carefully wiggling the cables should confirm there are no loose connections anywhere.

Only one amp has a loose RCA connector in the back but doesn’t seem to be the source of any problem I can tell.

That may be OK if it's not surface mounted on a PCB (i.e. there's a pair of jumper wires from socket to circuit board). But if it is surface mounted, you should repair it because it will only get worse and may pull the track off the PCB!