2. amps-preamps
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Mechanical buzz coming from the chassis

I have noticed a mechnical vibration causing a low level buzz eminating from the chassis of one of my monoblocks. The buzz is not audible through the system. It is only audible when your ear is close to the amp. Also if I squeeze the chassis the vibration stops.

The amp is a Quicksilver mid-mono with KT88 tubes.

Any ideas on how to solve the problem?
nick_sr
nick_sr OP
263 posts
 
I have the amps sitting on 1/4" thick cork mats. This helps, but regardless the hum is not audible from my listening position.

The other strange thing is that only one amp hums but both amps had relatively loose screws.

Also, soft mats and tightnening screws will eliminate the symptoms but do not address the root cause.
Post removed 
hifihvn
943 posts
 
Double check your bias also.A tube starting to short can cause this too.If this amp is easy to bias,you can try swapping the tubes between the two amps.If its hard,it may cause a problem that's not there.
raquel
841 posts
 
What Viridian said. They generally all hum, but some more than others. My tube amp is totally silent, but it is the exception.
nick_sr OP
263 posts
 
It appears that the hum is due to the bottom plate on the chassis casing vibrating against the side wall. I placed something underneatht the amp to pressure on the bottom cover and this has eliminating the hum.

I guess I could also loosen the screws and place a bit of blue tack between the two surfaces and then tighten everything again.
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