Re: Hum's gone, but there's still some noise left - mark

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OTL, Output Transformerless Amplifier User Group.

Re: Hum's gone, but there's still some noise left

Posted by mark on August 14, 1999 at 13:57:31

In Reply to: Re: Hum's gone, but there's still some noise left posted by Anand Mehta on August 14, 1999 at 09:09:13:

It does sound like you have good old thermionic noise. Since you must get your ears so very close to your
speakers to even hear the noise, you may not want to bother. If the noise was audible at your favorite
listening position, you'd have a real problem. White noise, or the stuff that sounds much like FM
interstation hiss, is almost always generated by the tubes themselves. No amount of power supply filtering,
at least with our amplifiers, will help.

There are some simple things you might try to possible eliminate the noise completely. I hear no such noise
with my amplifiers, but I'm a bit over the edge using my favorite 12SX7s, instead of 6SN7s. This is not to
say that I can't use the right 6SN7 and hear noise at all. Some 6SN7s are just plain noisier than others. I
have some GE wafer base 6SN7s the make the amp sound much like there's a small hurricane stuck
inside. These tubes are known to be just plain noisy. A better quality 6SN7 may just solve your problem.
6SN7s with more closely matched sections may help a lot too. The closer the sections are matched, the
more our amplifiers can take advantage of their inherent Common Mode Rejection Ratio (CMMR) and
cancel out this kind of noise. The is especially true using closely matched sections in the cascode stage.
That is the stage with the highest gain and it is most susceptible to the introduction of noise. You might also
try swapping 6SN7 positions and see if if it helps. You just might have a tube that is a bit noisier, or more
poorly matched, and it's behaving its worst in the cascode stage.

I hope this helps.

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Follow Ups Full Thread

Topic - Hum's gone, but there's still some noise left - Anand Mehta 09:34:46 08/13/99 (10)

Re: Hum's gone, but there's still some noise left - mark 18:30:37 08/13/99 (9)

Re: Hum's gone, but there's still some noise left - Anand Mehta 09:09:13 08/14/99 (8)

Re: Hum's gone, but there's still some noise left - mark 13:57:31 08/14/99 (3)

Re: Hum's gone, but there's still some noise left - Anand Mehta 08:53:21 08/16/99 (2)

Re: Hum's gone, but there's still some noise left - Brian Walsh 15:16:18 08/16/99 (1)

Re: Hum's gone, but there's still some noise left - Anand Mehta 19:24:47 08/16/99 (0)

Re: Hum's gone, but there's still some noise left - Dan McLaughlin 10:54:53 08/14/99 (2)

Re: Hum's gone, but there's still some noise left - mark 13:42:10 08/14/99 (1)

Re: Hum's gone, but there's still some noise left - Dan 18:48:39 09/02/99 (0)

Follow Ups

Re: Hum's gone, but there's still some noise left - mark 13:57:31 08/14/99 (3)

Re: Hum's gone, but there's still some noise left - Anand Mehta 08:53:21 08/16/99 (2)

Re: Hum's gone, but there's still some noise left - Brian Walsh 15:16:18 08/16/99 (1)

Re: Hum's gone, but there's still some noise left - Anand Mehta 19:24:47 08/16/99 (0)