2. amps-preamps
  3. 1208665904

Tube Amp Help/Problem

I have a new preamp. I notice when I turn the volume past 11:00 there is a very audible loud hiss.no hum. It increaes as I turn up the volume and at 11:00 is very audible from a listening position of about 7 feet away with no music playing. Is this a white noise issue? I tried switching the tubes to different positions (12AX7's) and no change/moving cables/interconnects away from power cords etc. This has a phono section built in which is exhibiting this issue. The other inputs do not hiss nearly as much or very little even with the volume cranked up which leads my to believe its not an impedence mismatch with my amp. I have read some of the posts that state they can hear hiss if they put thier ears next to the speaker. Mine is very audible 7 feet away. This is my first tube preamp so maybe this is normal.
autodexr
5 responses Add your response
mrjstark
1,112 posts
 
I have talk to Autodexr before and it is very unlikely that those tubes are kind
of high microphonics ones. As far as I know it should be low noise Philips
12ax7 tube in phono section as well as the preamp section . It is possible that
one of the tubes was demaged during shippment or just went bad and was
amiss during final inspection. It also could be the amp/preamp issue but I
doubt it. Also I would check cart loading (adj in the back). If all fails , you
know who to call or I could do it for you if you run into some problems but it
wouldn't be pleasant for ......?LOL :)
Keep us (me) informed.

Mariusz Stark
rodman99999
6,109 posts
 
At what position is your control during normal listening/loudest volume? If this noise is present at normal volume control levels: As Newbee stated, you may be using noisy tubes or have a cartridge output/phono amp mis-match. Tubes purchased for pre-amp/phono gain stage use should be certified low-noise, or their noise will be amplified exponentially by the time it gets to your speakers. If you are cranking the control way above normal: chances are you have a very acceptable signal to noise ratio at listening levels.
cruz123
586 posts
 
I can turn the volume to 11 o'clock on my Cary Sli-80 integrated and it's dead quiet from even 1 foot away, so the level of noise you're hearing seems excessive to me.
newbee
4,767 posts
 
Nothing particularily unusual about your situation but it is quite possible to reduce the noise by getting 'low noise' tubes (assuming that you don't have them, or that you present ones are worn out). They cost more but are worth it.

BTW, tube phono sections are often noiser than line stages, and matching the output of a cartridge and the output of a phono stage can make a difference, especially if you are using a low output MC cartridge.

You don't mention your other components but some tube pre-amps have high output and when coupled with amps with high sensitivity and with speakers of high efficiency you will have a hard time correcting pre-amp tube noise without some specific effort.
larryken
537 posts
 
it's a normal tube sound...tubes are never dead quiet...you learn to live with this tradeoff in exchange for all the pluses.
Larry
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