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Old 16th September 2005, 03:28 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?

dr._sleep
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Old 16th September 2005, 03:49 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...
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Old 16th September 2005, 03:59 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.

thanks,

dr._sleep
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Old 16th September 2005, 04:14 PM   #4
Magura is offline Magura  Denmark
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Quote:
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.

thanks,

dr._sleep

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.

Magura
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Old 17th September 2005, 03:47 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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