2. amps-preamps
  3. 1138816980

Midrange hiss....VERY slight...with my Dared pre

Let me start by saying that I've never owned a Tube preamp. I bought this piece 2nd hand, it has 'upgraded' tubes (installed by the previous owner, who seemed to know his stuff). The model is the SL-2000A. Anyway, after listening I noticed that there is a rather prominent hiss in the midrange. It sometimes is VERY unnoticable...but when the sound is playing in a certain range (perhaps around 2-5khz) the infromation is played with a slight hiss. Is this just what tubes do? Any help would be GREATLY appreciated.

Thanks.
radium141

Showing 3 responses by newbee

newbee
4,796 posts
 
Some tube preamps have a high noise floor. Some tubes are not 'low noise'. Some amps have high input sensitivity. Some speakers are very efficient. Any or all of these things, especially when combined (two or more), can cause a sound called "tube rush". Proper matching of components is essential to avoid this noise. If you list the names and spec's of your other stuff someone here can probably diagnose your problem.
newbee
4,796 posts
 
If you can't hear tube rush at normal/high volume listening levels, its NOT a problem! Even more so if you only hear it when you've got your ear within inches of the tweeter/midrange. Many fine units both SS and Tube, operating properly, will reveal their noise floor depending on the input sensitivity of the amp and the efficiency of the speakers.
newbee
4,796 posts
 
Interestingly it may be just that and new has nothing to do with it. I have two new amps, both with high sensitivity (.5v and .8v)and two older amps by about 12 years which have much lower sensitivity (1.5V), some of the older ones even go down to 2.5v or less. Higher amp sensitivity makes the pre-amps job easier and facilitates the use of passive pre-amps for those interested. The speakers at 89db are moderately efficient.

Personal story - Had some Acustat panels with an 82db. With my SP10 and the matching ARC 115II amp my system was dead quiet. The I got some Quads - only 4db difference - all of a suden I could hear noise. Then I got a new amp with higher input sensitivity (.8v) wow - did I have noise now! Thats when I started to paying attention to low noise tubes in my pre-amp. Thats how it goes. Ask someone who uses high efficiency horns about noise! :-)
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