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Subwoofer rumble issue

I’m having a hard time solving a problem that seems to come and go. My subwoofer will rumble uncontrollably when playing records at a higher volume. If I turn the volume down sharply it goes away but when I creep the volume back up it comes back. I’ve tried isolating my turntable as much as possible with diy books, isolation feet, etc. (I don’t want to buy an expensive isolation platform unless that really is the issue.) Any thoughts on what I can do to fix this? Thx!
paulgardner
georgehifi's avatar
georgehifi
10,312 posts
 
Where and in what are these tubes situated, if in a tube preamp (model?) and your using the aux input you are still fully using the output buffer tubes of the preamp, but you say they seem to be ok?
So then I'm affraid we come back to the air-born feedback.

Cheers George
georgehifi's avatar
georgehifi
10,312 posts
 
big_katydid
The combination of TT, room, track and record warps led to a loop that saw the drivers very quickly oscillate more and more until the paper cone literally tore open around the center area, this took less time than I could get over and turn the volume down
Yes, this is another way the air-born  runaway feedback oscillation can start. The wrap was the initializer, then the air-born takes over and just runs away getting louder and louder till something goes bang! 

Cheers George
paulgardner OP
183 posts
 
The tubes I checked are in the CM II integrated. 4 power tubes, 3 12AU7s and 2 12AX7s. I’m running the Phonomena II+ phono pre which is solid state. I assume some of the small tubes in the CM II are still being utilized in the signal path - I believe the center position 12AU7 is the Preamp tube. 
paulgardner OP
183 posts
 
Just did a quick test just for fun and placed a pillow under my turntable and the rumble is gone! Super tight bass! So maybe it’s not actually airborne?? Just need some extreme isolation? Hmmmmm interesting 
georgehifi's avatar
georgehifi
10,312 posts
 
Almost certainly one or two of the 12au7's will be the pre stage output tubes.

Cheers George
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