Amplifier started humming

[Scrappy]

cool remote that's carved out of wood and that works through walls and has only 2 buttons: louder, quieter.

Amazing!

 

[restorer-john]

If you have one of those killawatt style consumption meters, plug it in line and watch the consumption in watts- humming vs not humming. If the consumption skyrockets when the hum kicks in- stop using the amp and take Bob's advice. It only takes one cap, be it rectifier or even coupling/bypass to go and there will be carnage.

 

[TrevC]

If you have one of those killawatt style consumption meters, plug it in line and watch the consumption in watts- humming vs not humming. If the consumption skyrockets when the hum kicks in- stop using the amp and take Bob's advice. It only takes one cap, be it rectifier or even coupling/bypass to go and there will be carnage.

I think the flames and smoke will have given that away. It's just a buzzy transformer, FFS.

 

[restorer-john]

It's just a buzzy transformer, FFS.

Excess consumption causes transformers to make more noise than normal. You didn't know that?

 

[TrevC]

Excess consumption causes transformers to make more noise than normal. You didn't know that?

You want an argument. Sorry, won't bite.
If it was drawing a large excess of current it's pretty obvious there would be other signs present.

 

[tmtomh]

No one can be 100% certain without testing, but with that said, by far the most obvious likelihood is transformer hum caused by DC in the AC line.

The fact that the hum is mechanical from the amp and not coming through the speakers is a dead giveaway, and the fact that the transformer is a large toroidal unit makes it even more likely since toroidals are well-known to be especially susceptible to DC-induced mechanical hum - and the bigger the toroidal, the more likely the hum will be audible/loud.

The troubleshooting steps are, as some have noted above, pretty clear.

1. Make sure the large screw in the center of the transformer is fully tight. IMHO it’s unlikely this will be the source of the problem, but it makes no sense not to check it first.

2. Try turning off or unplugging any fluorescent lights, lights on dimmer switches, TVs, fridges, or other large appliances in the house. Again unlikely to fix it imho (DC can come from a neighbor’s house or just the overall grid in your area), but worth a try.

3. Buy a DC blocker. They only do one thing, but they do it exceptionally well. If it’s DC in the AC line, you’ll confirm it instantly - DC blocker will reduce the hum 90-100%.

Good luck!

 

[egellings]

Not through the speakers ... the box itself started making a ~60 cycle, kind of ragged sounding hum. Loud enough to be audible over quiet music. I unplugged it and started it back up again, and the hum immediately came back ... and then vanished.

Background: it's a 20-year-old Unison Research Unico integrated amp, with a tube preamp (pair of 12au7s) and mosfet power section. It's been in storage for 9 years, and a month ago I set it up again after we moved into a house that has room for this stereo system. I've never had any trouble with it. My plan was to sell it, and replace with something more modern and sensible (and solid state), but I remembered that I really like the thing. It's just so pretty, and feels so good, and has this cool remote that's carved out of wood and that works through walls and has only 2 buttons: louder, quieter. So I'd be bummed if the thing died.

What could cause a whole amp to spontaneously hum, and then spontaneously stop? Could it be electrical interference in the mains? A capacitor starting to give up the ghost? A tube problem?

It forgot the words...

 

[Cars-N-Cans]

I think the flames and smoke will have given that away. It's just a buzzy transformer, FFS.

No, he is right. Something is loading it down. I came in to say the same thing restorer-john was going to say. All sorts of things can do it. I even had a laser printer that caused an AVR to literally dance across the shelf under the TV. It was causing one half of the AC sine to vanish from excessive load which caused the transformer to saturate and make thunderous noises.

But, I would be looking at the caps and rectifiers as a start. Could even be something in the amp section, or something distorting the mains. But it’s not something to ignore. Had an eBay TDA1554 kit amp I made in high school do the same thing. Ended with a totally shorted output stage with lots of smoke, flame, and 120 Hz rectified DC straight into the speakers. Fortunately the fuse intervened before it got too dramatic. Same scenario, too. Pulled it out to play with it again after long time in storage.

 

[TrevC]

No, he is right. Something is loading it down. I came in to say the same thing restorer-john was going to say. All sorts of things can do it. I even had a laser printer that caused an AVR to literally dance across the shelf under the TV. It was causing one half of the AC sine to vanish from excessive load which caused the transformer to saturate and make thunderous noises.

But, I would be looking at the caps and rectifiers as a start. Could even be something in the amp section, or something distorting the mains. But it’s not something to ignore. Had an eBay TDA1554 kit amp I made in high school do the same thing. Ended with a totally shorted output stage with lots of smoke, flame, and 120 Hz rectified DC straight into the speakers. Fortunately the fuse intervened before it got too dramatic. Same scenario, too. Pulled it out to play with it again after long time in storage.

You have to be careful of that 120 Hz rectified DC stuff.