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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
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
geoffkait's avatar
geoffkait
23,365 posts
 
Ya think? 🤔
big_katydid
50 posts
 
what I notice on this topic is that when listening to recordings posted on youtube if the track is from vinyl you can often tell as there is obvious woofer pumping, I assumed wrongly that a signel might have been high passed to get rid of some very low frequency hash, apparently not. Many dance/electronic 12 inches not available on digital format have been uploaded and show this.
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