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Old 16th September 2005, 02:28 PM   #1
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Default 120 Hz Buzz Unplugged

I happened to place my ear close to my Khorn this morning and heard a faint 120 Hz buzz. Odd because my entire system's power is switched on an off from a single source, a rack mounted PS filter.

A monoblocked SE EL84 amp powers the speaker, so I pulled the PS cord and input cable, still buzzes. If I disconnect the speaker wire from the amp the buzz stops (if this didn't stop it I'd have my ears checked).

Question is, how can an amp, disconnected from any 120 v power supply and source generate a 120 Hz buzz when connected to a highly efficient speaker like the Klipschorn?

Do I need an exorcist? Maybe my home was built on a burial ground?

Any ideas, suggestions?

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Old 16th September 2005, 02:49 PM   #2
EC8010 is offline EC8010  United Kingdom
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Default Bell, book, and candle?

Sounds as though the output transformer (which is a coil) is picking up a stray magnetic field and passing it to the loudspeaker. Now, the more interesting question is, "Why is it 120Hz and not 60Hz?" I'd suspect that there's a transformer or motor (or perhaps even a fluorescent light) nearby that is saturating and leaking 120Hz. You'll have to go round switching things off. Possibly by candlelight...
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
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Old 16th September 2005, 02:59 PM   #3
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I didn't have time this morning but I'll put my oscilloscope on it to check the frequency. It was not a hum that was audible, but it could be harmonics of 60Hz through the tweeter and/or midrange horn.

I do have a dimmer switch in the room but it is 20 feet from the amp. Nothing else was powered up nearby.


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Old 16th September 2005, 03:14 PM   #4
Magura is offline Magura  Denmark
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Originally posted by dr._sleep

I do have a dimmer switch in the room but it is 20 feet from the amp. Nothing else was powered up nearby.



Hmm, a light dimmer, the No. 1 on the top 10 of nasty little buggers that causes noise on the mains.

Try switching off the dimmer and see if the problem persists.

Everything is possible....to do the impossible just takes a little while longer.
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Old 17th September 2005, 02:47 AM   #5
Enzo is offline Enzo  United States
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That dimmer might be 20 feet away, but the wires from it go all over the place.
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