2. amps-preamps
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Any way to reduce pre-amp noise floor?

I have had my CJ ET3-SE tubed pre-amp for about a year now. When my system (McCormack DNA 500 amp, Esoteric X-05 CD, Aerial 10T speakers) is on and the CJ is set to "0" volume there is dead silence. However once I move the volume to to any level above zero ( no music playing, of course!) I hear a very soft but audible white noise. When I return the volume to zero the noise vanishes. This concerns me because I suspect that once the music begins to play, this noise floor becomes part of the overall sound.

This is my first "separates" system so I'm not sure if this is just a standard preamp phenomanon or if it is perhaps a sonic signature of CJ or if there is some real issue that needs to be fixed or can be tweaked. Any comments/suggestions will be greatly appreciated.
shoff
onhwy61's avatar
onhwy61
5,251 posts
 
Exactly how loud is the noise? Is it only audible when you place your ear next to to the tweeter dome or is it clearly heard at the listening position? Does it get progressively worse as you raise the volume control setting or stays the same? Have you ever heard the noise when music is playing?

It could be the normal sound floor of your electronics. It could be the sound of a noisy tube. It could be noise coming in over the power line. Answering the above questions will help narrow the possibilities.
mechans
3,048 posts
 
My first thought was a tube issue as well. Tubes are frequently noisier than SS. In a pre-amp, any tube in the signal path and especially in a gain stage, should be very carefully selected for low noise. Even then, as tubes age, they can develop noise problems.
I find the tube sonic so appealing, that I am willing to sacrifice a very, very low noise floor. If it isn't audible with music playing you might want to live with it.
elescher's avatar
elescher
114 posts
 
Look into improving the grounding on your system.
mulveling's avatar
mulveling
1,959 posts
 
If the noise increases with the volume control, then that at least rules out the preamp's buffer output stage, and your amp.

In a review of the ET3-SE, it's mentioned that this unit uses a single 6922 tube for voltage gain. They didn't mention whether that tube comes before or after the volume control. If before - then it would be a prime suspect as the noise contributor. You could buy a guaranteed "low noise" 6922 tube from a trusted tube vendor, and see if that helps. If your source is an MC phono stage, then that could also be the (likely) cause of noise.

If all gear is in spec and the tube in question is not a noisy specimen, then it may just be that you've got an exceptionally high sensitivity amp & speakers - which would imply that you'd have to listen with the volume control quite low (i.e. you're throwing away gobs of gain - a prime candidate for a passive, though I still love the sound a good tube preamp even with some excess gain and noise floor).

BTW, being a vinyl and tube 'phile - I don't find a modest noise floor of the white noise variety (i.e. NOT ground loop hum) to be of detriment to the music.
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