2. amps-preamps
  3. 134646-90310

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 2 responses by newbee

newbee
4,794 posts
 
Could be as simple as needing some very low noise tubes. Could also be too much gain for your amp/speakers and the 'noise' issues could be solved by using a fixed in-line attenuator. But that turn on 'buzz' and high frequency noise after 24 hours, I don't know. But then I would never leave a tube unit on for 24 hours......The turn on buzz is probably nothing more than the unit stabilizing, something many pre-amps avoid by having a mute circuit which engages on turn on (for up to several minutes).

Tackling the tubes first is a good place to start. Sooner or later you will have to change them out, so even if this is not 'the' problem having the spare set is a good idea anyway. 
newbee
4,794 posts
 
Rothwell -  stock 10db in-line attenuators should work just fine. No real downside unless you have ultra high end stuff and you are anal! :-) You can select other values if you want. Lot cheaper than trying to mod your pre-amp internally.  BTW, if you are changing tube brands be aware that you will want to insure that their 'tonal' balance is one that you will want in your system. Do lots of research on this before you leap and beware of salesmen's advise and advise from folks who don't know much more about tubes than you do, they abound! :-)
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