I have a few boxes that buzz as soon as you plug them in. One of them can even be heard 10 feet away. Does that mean they're on their way out?

(1) A DC component in the AC line, often introduced by other equipment such as refrigerators, etc.
(2) Vibration caused by loose sheetmetal shieldings, etc. which will vibrate (keep in mind that the transformer behaves like an electromagnet with the power switching at 60 times/second.
(3) Loose lamination in the transformer core. Most transformer cores are made of laminated metal plates rather than a single chunk of metal. If they delaminate, they can vibrate.
(4) Transformers itself loose. As they normally do vibrate to some extent, a loose transformer can certainly cause the panels to resonate and magnify the vibration.

quote:

(3) Loose lamination in the transformer core. Most transformer cores are made of laminated metal plates rather than a single chunk of metal. If they delaminate, they can vibrate.

The same phenomena can be heard in the case of fluorescent lighting fittings with the traditional wirewound 'choke' or 'ballast', the effect is often amplified by the metal casing of the luminaire.

Hmm, thanks for the replies. Interesting stuff. So it sounds like transformers very rarely go bad?

quote:

Originally posted by Reli:
Hmm, thanks for the replies. Interesting stuff. So it sounds like transformers very rarely go bad?

Transformers are sooo simple they are truly nothing more than a coil of wire looped around an iron core. About the only thing that causes failure is heat, overcurrent, and corrossion which shorts them out or breaks the continuity. Heat destroys the insulation and/or burns out the winding.... corrossion -- destroys the insulation between the wire and connections.

A few drops of super glue in the
right place might kill the buzzz

What about keeping them plugged in all the time, versus unplugging them when not in use?

could be a fly or a bee

quote:

Originally posted by Reli:
What about keeping them plugged in all the time, versus unplugging them when not in use?

Instruction manuals invariably recommend unplugging any unused equipment. Firstly, they continue to suck up an ever so minute amount of power but also because power line issues, such as surges and lightning strikes could cause catastrophic damage to connected equipment. The chances are small of course.

But conventional wisdom says every electric device (except maybe old refrigerators and washers/dryers and oven/ranges) all have micro electronic controllers and as such, all require a power reducing/converting component. And of course those are always connected to power. So it's up to you. Most of my stuff are plugged in all the time and I have never had one power surge related issue with any of my electronics.

quote:

Originally posted by Reli:
What about keeping them plugged in all the time, versus unplugging them when not in use?

Probably better to connect them
to a power bar with a switch.
Than you can turn them all off.

Tranformers use metal plates that glued together.
If some plates come loose than they will vibrate.

Another odd problem could be thr rectifiers
not making it full wave, working at half wave that can make more noise.
Open circuit on the board.

quote:

Originally posted by Reli:
What about keeping them plugged in all the time, versus unplugging them when not in use?

To me it seems that keeping bbx's plugged in will eventually burn out transformer because the power switch is after the transformer line, which means it stays hot all the time. On most other electronics like home audio the switch is before the transformer.. This is only my opinion