Sounds like you are hearing a noisy tube, or the noise floor of your tube buffer. I'll bet if you take it out of the circuit the noise will go away.
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I really don't know if it is AC. The reason I went in the direction of it being due to the tube buffer was because that was suggested to me by someone who works for a line conditioning manufacturer. Do you have some experience with RFI making that sort of sound? I would appreciate any help you could give me.
Dougm, Sounds like taking the buffer out didn't make a difference. I can't tell from your post if you have done this yet, but if not....Disconnect everything in your system (cables and IC's) except your amp and speakers and see if you have the "sound". If you do you have at least isolated the problem to your amp and/or power. Then work backwards thru your whole system one component at a time, very methodically. For example add your preamp and IC's to amp - and listen with out turning it on. No "sound", now turn it on. Also rotate selector switch before adding Ic's from sources and listen. Repeat process until you isolate the noisy component. Then feed back.
Thanks David99 for the input. I will check my bass with and without the buffer. I do think the buffer adds a wee bit of depth to the instruments, as well as a tad of warmth, but I may need to rethink if it turns out to be the source of the noise.
Newbee, I will do as you recommend and isolate each component. I did not have a chance to remove the tube buffer yet. It's funny but for the last several days the previously noisy left side is absolutely quiet, while the right side still has a bit of crackle. I will post my findings after I have isolated everything.
Well I disconnected, then reconnected everything while listening in between. I discovered it is the Musical Fidelity tube buffer causing the noise. I called the importer and spoke to a technician. He told me that I should not connect the buffer between the pre-amp and amplifier. He reported that doing so could cause damage to my speakers and/or amp. The reason is that when the buffer is first powered up a DC spike is created that is passed through the output of the buffer. If the amp is already on this spike could damage the amp, blow a fuse, or blow out speaker drivers. The tech recommended mounting the buffer in the tape loop of the CD Pre24. I did this, and found that the noise I was getting through my speakers was almost completely eliminated. The left speaker is now dead quiet, while the right has just a hint of noise with the volume set medium high(which is about the limit for my room). I also noticed a little more freedom in the area of dynamic shifts from the amp. This was confirmed by viewing the amp meter on my line conditioner. Without the tube buffer the music is clear,detailed but a bit flat. The buffer adds that bit of livelyness to the sound making it sound more real. Therefore I will continue to use it. On my system the bass does not seem to be adversely affected. Thanks to everyone for their help.
I think the really important part of this "problem" is that it may not be a problem at all. You said:
" When I put ear close to the speakers I can hear what sounds like something frying in a pan"
If you had to get that close to the speaker to hear it, and if the noise does not increase when you turn up the volume, then don't worry about it. Just about every amp, tube or transistor, can send a little bit of noise into the speaker. Tubes always send a little noise, that increases with age, which is one of the things that can tell you when to replace them.
Don't worry about it.
Thanks again everyone for your responses.
Golden Ears I think you are right about not worrying about it too much. I am pretty happy with the sound the system is providing me. It is the best I have had to date. It was just one of those things that you can get carried away with trying to eliminate only to discover that in the end it really didn't make any audible difference when sitting in the listening position. At first I was a bit concerned, but now that I am sure it's comming from the tube buffer, well I can live with it. I suppose it might be covering some low level detail, but I really can't discern anything. Perhaps the background would be blacker, who knows. I like the way the system sounds and that in the end is all that matters. In a few years I will probably get the upgrade bug again anyway!!