Got Noise?


OK Guys, need your help with this one. Recently I've noticed a fairly high degree of background noise (sounds like a "ffffsss" coming through my system at idle. The noise is only audible when the amp is turned on, not any of the other components. The amp has been tested by the manufacturer and he reports no issues. (Amp is a Modwright KWA150 and I asked Dan to check this for me when he did the "SE" upgrade a month or so ago). The level of noise is audible when I am playing music only at very low volumes, which has been the case over the past 4 months since we now have a baby on board. In fact, it is possible that nothing has changed but the simple fact that before the baby I was listening at higher volumes and did not notice the background noise. On the other hand, it is somewhat intrusive and if there is something going on elsewhere then I'd like to address it. FYI I have a 20 amp dedicated line to my system and have an Environmental Potentials 2050 surge suppressor/noise cancelling device installed on the panel, which I had my electrician confirm has been correctly hooked up. Is it possible that something is happening at the pole where I have a transformer shared by two other neighbors? I can't decide whether this is a new problem that has developed or simply an old problem that I did not know was there until I started listening at much lower levels in the past few months. Tell me, when your system is at idle how much noise do you hear when you put your ear to the drivers? Or from your listening position?
dodgealum
05-10-12: Bombaywalla
Merely saying that unless the amp is on, the speakers are not driven thus any noise generated in the electronics will not be heard. This is obvious to me but no one else including Almarg stated it so, what am I missing here?
Yes, I noticed that too, and you're not missing anything :-)

Good comments in your post.

Best regards,
-- Al
Mark,

It could also be something coming into the preamp. I would unhook everything from the preamp except the AC power cord and the output cables to the amp. This would be like starting from square one.

If you hear any noise, it is either the cables from the preamp to amp or the preamp itself, (probably a tube).

If you do not hear any noise, start plugging your components back in to the preamp ONE AT A TIME and listen for the noise. One of these will be the culpruit. Which, now you will need to determine if it's the unit itself or the cables from it to the preamp.

Sorry, but you'll need to troubleshoot this thing from the very beginning. I just helped a friend do the same thing. Noises/hums/buzzes are a pain in the ass to find. Starting from square one and working one at a time is the only way to find it.
Mofi,

Note that Mark indicated that "the level of noise is audible when I am playing music only at very low volumes." That would appear to indicate that the noise level is insensitive to the volume control setting, which would mean that it is not being caused by anything upstream of the volume control.

Best regards,
-- Al
Guys:

I may have been unclear and so driven the discussion off the rails. Almarg: your synopsis "a" is not correct: amp on + preamp off = noise. Again, none of the other components make the hissing noise alone or together. Just the amp when on alone or when on and the preamp is unmuted. I moved the cables as best I could away from the power cords and the noise is significantly diminished. I think this is the culprit and the sound will likely disappear if I can find a way to get the ICs between amp and preamp completely away from power cords.
amp on + preamp off = noise
OK. So that rules out the preamp as the source of the noise, leaving the cables as what should be focused on, as you are doing. If those efforts aren't successful, the Mogami's (or other shielded balanced cables) would seem to be the logical next step.

Best regards,
-- Al