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Amplifier hum: Does it need repair?

I have a Bel Canto Evo2 amp. Lately, I've been noticing a low level hum from my system which is intermittent in nature. Today, it seemed worse, and it didn't go away in a few minutes like before. I turned off the turntable and determined that the hum wasn't eliminated when I moved the preamp source selector to CD. It also wasn't affected by the volume control. I turned off my Supratek tube pre-amp and determined that the hum persisted. Then I unplugged the two Vandersten subs and still heard the hum. Finally, I took the power cord out of the power strip and plugged it diectly into the wall. The hum was still there. The only thing I haven't detached are the speaker cables. It almost sounds like the hum is coming from the amp and not is not coming out of the speakers, but I'm not sure about that. I really don't want to have to ship it back to the factory for a repair. What do you think?
mlkiz
9 responses Add your response
piezo
304 posts
 
i've got one for ya if anyone wants to diagnose it. I have a VTL monoblock with an intermittent hum. sometimes it is preceeded by a volume spike (in a monoblock that is supposedly run wide open whith volume controlled at the pre...and it follows the amp so not a pre issue). the hum always goes away if you toggle the power switch (with tubes you don't even hear the toggle effect on the music the hum just goes away). sometimes it will go away if the other amp or the pre is toggled. sometimes it can go away...or start again if you wiggle the audio input at the amp. i wish the darn thing would break so i could send it in for repair. shipping for a checkup is pricey
audphile1's avatar
audphile1
4,922 posts
 
Thorman may have your answer.
If you have cable tv, try to take the cable wire out of the first point of entry into the system, which is probably a cable box. But remember, disconecting the cable box would not show anything. Only taking that cable wire out will tell you if it's the problem. If your amp hums after that, it's something else. But if it's the cable tv, musicdirect.com sells this little thing called Mondial Magic Box

http://www.amusicdirect.com/products/detail.asp?sku=AMONDBOX

My amplifier was humming and it was the cable tv, so I bought it at music direct. Problem solved....Good luck.
druhot
1 posts
 
I had a problem with my CA 201 and thought it was a ground loop problem. Tried for months to figure it out. Finally sent my amp to classe and it was the control panel that needed to be replaced.
crest
22 posts
 
I had a similar problem with a McIntosh power amp last winter. I discovered the source causing the amp hum was from a space heater I was using, and it wasn't even on the same line as the amp. See if an appliance could be the culprit.
kr4's avatar
kr4
3,678 posts
 
Before I put in a dedicated line and really solved my ground loop problems (which I had been masking with a so-called ground loop interrupter), I had intermittant hum/noise directly from the eVo6 chassis when certain halogen or fluorescent lamps were used on the same power line. It usually went away with lamp recycling.

In my other house, which had better AC all along, the eVos are just fine.

In your case, it could be DC or RF-induced noise on the AC lines.

Kal
thorman
1,262 posts
 
Also is it possibly cable t.v connection on the same line? Just a thought!
wepratt
29 posts
 
If you determine that the hum is definitely coming from the amp or pre-amp, it might very well be a DC problem. I had this happen with a receiver and it nearly drove me nuts. Tried all sorts of tests and solutions and finally bit the bullet and bought a PS audio Humbuster which solved the problem instantly.
newbee
4,767 posts
 
In addition to Rich's comment, you can determine the source of the hum by disconnecting everything from the amp (when its turned off!) except for speaker cables and the speakers. Turn it on, no hum? Good. Turn it off, plug in IC's from pre amp (with all other IC's disconnected from the preamp) - same scenerio as above, til you find the source of the hum.

Also put you ear next to the amp - you might hear a 60cycle buss from the transformer. Put you ear next to the midrange/tweeter and see if you hear a hum.

Lastly, make sure your IC's are not lying parallel to power cords or power sources, transformers and the like. Make sure that you don't have stuff with transformers near your pre-amp.

In short, though its too late for this post, take your time and be methodical in your approach.
rar1's avatar
rar1
1,769 posts
 
Have you tried a cheater plug (3 prongs to 2 prongs) on the Bel Canto's power cord? This would rule out/rule in a ground loop problem.

Regards, Rich
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