I saw your thread yesterday, but was a little reluctant to respond, with what I thought the problem might be.I then saw "Joeabrams" reply, and said Joe nailed it. When I checked again this morning, and saw "Sean's" reply, I said there is the frosting on the cake, and it looks like an easy, inexpensive fix...Your reply of already having the Zobels in place, then brought me back to my slightly out of the box thinking.
So here goes... I viewed your system, and I noticed a smallish room 10x14 with a wall mounted shelf.
Could it be, when you turn up the volumn, that enough energy from the room's primary resonate frequency point is exciting the wall, and shaking your wall mount shelf, which would shake the the preamp, and it's tubes. Heck, if you can yell into a tube directly, and have the sound of your voiced reproduced at the speakers, then why couldn't a vibrating wall induce some distortion into the tubed preamp, and have it appear as breakup at the speaker during loud passages.
Can you temporarily replace the tube preamp with a solid state unit, or move your tube pre from the wall mount temporarily. Another thought would be to try some sort of tube damping device.
A/gon member Jax2 (Marco) complained of a very similar problem awhile back, but I fail to reply then, again do to my reluctance, and lack of experience with tube equipment.
I told you it was slightly out of the BOX thinking.
Good Luck, Dave
So here goes... I viewed your system, and I noticed a smallish room 10x14 with a wall mounted shelf.
Could it be, when you turn up the volumn, that enough energy from the room's primary resonate frequency point is exciting the wall, and shaking your wall mount shelf, which would shake the the preamp, and it's tubes. Heck, if you can yell into a tube directly, and have the sound of your voiced reproduced at the speakers, then why couldn't a vibrating wall induce some distortion into the tubed preamp, and have it appear as breakup at the speaker during loud passages.
Can you temporarily replace the tube preamp with a solid state unit, or move your tube pre from the wall mount temporarily. Another thought would be to try some sort of tube damping device.
A/gon member Jax2 (Marco) complained of a very similar problem awhile back, but I fail to reply then, again do to my reluctance, and lack of experience with tube equipment.
I told you it was slightly out of the BOX thinking.
Good Luck, Dave