noisy tube preamp


I'm fairly new to tubes but have recently acquired a tube preamp. I'm really liking the air and the soundstage it provides, something the solid state stuff haven't done as well but the one issue I have is the elevated noise floor. It's really only audible when no signal from the source is being played, like when the system is simply on or when the song stops. Also there is an occasional quiet, short lived buzz from the speakers that pretty much goes away after the preamp warms up and lastly, after the unit has been on for several hours, like 24+ it will start to emit a high frequency pitch that also is only audible with no music playing but it is louder than the inherent noise floor of the pre. My question is, is this something I can remedy by rolling tubes or is it something that has to do with the pre itself like the design or a failing part? Btw, it's a jolida fusion preamp.
lukaszwk

Showing 4 responses by atmasphere

Also something that I may have misrepresented is that the buzz (not the high frequency pitch) i hear is intermittent and comes on every few minutes until the pre warms up so it's not a constant thing.
That is consistent with a possible bad tube.
@lukaszwk You might try TubeDepot.com I don't know of anyone selling tubes in Chicago, but I'm sure they are there.

I would not regard the age of the preamp as having anything to do with tube condition! Who knows if the tubes were any good when they were first installed??
Also as far as voltage gain from the pre, I'm pretty sure that is also the issue, I have never dared to play it louder than maybe 11 o'clock position on the volume potentiometer because it's starting to clip a 300 watt amp so the in line attenuator sounds like might be a good idea although I'm pretty wary about putting another thing in the signal path.
@lukaszwk, I would try other tubes before doing anything with an attenuator. Its not that weird for an older used tube to get noisy and microphonic. If you replace the tubes, it might be nice and quiet.
after the unit has been on for several hours, like 24+ it will start to emit a high frequency pitch that also is only audible with no music playing but it is louder than the inherent noise floor of the pre.
That is a form of something called 'microphonics' and is a property of all active devices. Tubes have it more than solid state, and its definitely something that you can get rid of by changing a tube!