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Ringing from the tweeter

Hello fellow Audiogoners,

The ringing began about a year ago or longer in the left tweeter. It sounded like tuning in to radio stations in the old days, which I attributed to my Rogue Audio 99 preamp's tubes going bad. At first it was intermittent, then more and more present. It was audible and annoying when changing sides or records, even with the volume all the way down, but not apparently audible with the music. I had a rare listening session when the ringing was not there, but once it began it was pretty much always there. Muting the preamp would get rid of the noise so I assumed the problem was the preamp tubes, not my M-180 tube monoblocks.

About a month ago, I installed new tubes in the preamp, four NOS hand-picked and thoroughly tested by Andy from the VTS. The tubes are dead quiet and sound terrific, but just a week or two after I put them in, the ringing from the right tweeter this time began again, first intermittent, now pretty much constant, just as before. Again, muting the preamp gets rid of it.

Andy told me that the 6SN7 tubes should last years so I'm quite upset the problem returned so fast. Any idea what may be causing the ringing other than the new tubes going bad so fast? Is the preamp somehow “overstressing” the tubes, for lack of a better word, and needs to be checked out? The tubes are the type that can handle higher voltage, btw. The only other source would be my solid state phono preamp or the cartridge, which I think is rather unlikely.

I’d appreciate your opinion or suggestions.
actusreus

Showing 1 response by lewm

lewm
13,476 posts
 

What’s a “high gain” slot in an all tube device? The tube supplies any gain, so gain cannot be greater than what the tube can provide. I’m guessing that Actusreus’ preamp was picking up RF and that the tubes per se were not at fault; he probably needed shielding or to move his preamp elsewhere in his room or to check any digital devices that can emit RF.

if you arrange 6SN7s in a cascode topology, you do get very high gain and very wide bandwidth capable of picking up RF ieither radiated from some outside source or dumped into the signal path. My Atmasphere MP1 uses 6SN7s. I have found that nearly all the best sounding NOS brands (RCA, Kenmar, etc) are very microphonic, unusable in the linestage gain position. One notable exception is Brimar 6SN7GT, with a brown phenolic base. That’s what I’m using now. 

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