Subwoofer rumble issue

Almost certainly one or two of the 12au7's will be the pre stage output tubes.

Cheers George

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

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

Back in the TT days Paul you had speakers that were lucky to go below -3db@50hz, now there’s subs that can go 2 octaves lower, with 1000w plate amps, this is what I found with Linn LP12/Ittok/Supex1000 and my Kef B1814’s 19hz, then CD came along, and then no problems.

Cheers George

He's already proved he has air-born feedback, do the test above as in my first post, the way Ivor Tiefenbrun laid out all those many years ago,  (know who he is?)
Or sell the OP your useless car valve springs, or your magic pebbles, better still give them to him as they will end up in the bin, even better still give something constructive to these forums, instead of your constant malignant voodoo talk.
  http://www.machinadynamica.com/machina31.htm
 

No not telling you to, would never do that Paul, but beside putting the TT in another room, it was the only other fix for me with bass that goes to very low frequencies.

Just dawn on me, if you have any tubes in the chain, these can go "microphonic" some call it "euphonic" (w**k w**k) and this can cause runway bass oscillation also.
If you have then do the finger nail light tap test on these just like the plinth test, but without the stylus on the record this time.

Cheers George

Yeah unfortunately you have to live with the negatives of the rumble filter is doing to the low bass, shame as that was what getting a sub woofer was all about.
Like I said the only way to totally get rid of "airborn feedback" as you found you have with the way I said to test for it, is to have the TT in another room as I did and which worked a treat, best bass ever, as my 2 x Kef B1814’s in 2 11cu ft enclosures were tuned down to 19hz fs each.

Cheers George

Subsonic rumble filter! All better! I understand it’s a “bandaid” approach but it totally worked and my stereo sounds amazing again! YES!!! Thanks again everyone!

Yes until you figure out how to stop the airborn feedback, it is a band aid, as it’s taking away what stereo info there is below 140hz
Quote: "The circuit "monos" the low frequencies below 140 Hz"
I still don’t understand how this will fix the airborn feedback test I asked you to do though, did you try it again with this filter in place?

Cheers George

A subwoofer on springs? Help, I’m gonna die laughing. That’s a joke right? Tell me it is a joke....

Yeah it’s called the humanless pogo-box. Just GK with his voodoo

Isolate the sub from the rest of the system by putting it on short stiff springs. You know, like Super Stiff Springs. Trademark. Problem solved!

Yeah, they're called valve springs from an auto engine, $1 each from auto wreckers, not $13 each!!!!!

This filter you bought, is for very low arm cartridge 7-12hz resonance (below 20hz), this you can’t feel or hear, it’s just very slow woofer movement.
I think from what you described you problem is far higher, around 30-70hz this you feel and hear like an ever increasing earthquake.

If you have floor standers with half decent low bass as your main speakers, try doing the "donk" test again but with the subwoofer/s turned off this time. try it even if they are just stand mounts also.

Cheers George

paulgardner OP10 posts

11-18-2019 5:27am@georgehifi you were spot on. Stylus resting on a still record then tapped the plinth and the sub rumbled like crazy. Would a subsonic filter fix this or what’s the best solution in you eyes?

There you are.
The the initial sound of the "donk" tap of your finger is the first mechanical starter vibration, but the growing intensity of the following earth quake rumble is "air-born" feedback, which you have end of story, don't listen to others trying to sell you stuff like special voodoo springs ect. 

You can hang your turntable as I even tried from the ceiling on fishing line and it will still happen.

The only way is to get rid of the broad band frequency that’s doing it (the sub) notch filter may help a little, but it needs to be board band, may as well not have a sub then. No isolation BS in the same room is going to be a fix for this, if hanging the turntable in the air couldn’t fix the problem.

Or move your turntable to a place where the air-born vibrations can’t get to it as much, which is what I did, in the next room. Then I could wack the plinth even harder and only get the initial "donk" sound nothing after it. Then my system sounded awesome in the bass, you won’t believe it, I had sub bass unit’s <60hz (2 x Kef B1814 in 11cuft enclosures each) that were flat to 19hz!!!! Those bass drivers made the Kef B139 look like tweeters

Cheers George

paulgardner
My subwoofer will rumble uncontrollably when playing records at a higher volume.

Your are getting "air-born feedback", and it can’t be cured with better stand mounting.

Do this.
If you just put the stylus on a record NOT spinning, turn the volume up to your normal position, one hand on the volume control, then gently tap the turntable plinth, you will see you’ll get "runaway feedback", which just gets louder and louder.
The only way to cure this is no subwoofer or the turntable goes in another room.

Cheers George

paulgardner OP3 posts11-17-2019 2:11pmGeorge- I’ll give that a try when I get home tomorrow. Thank you

Yep air-born feedback.
I bet nearly 100% it’s your problem.

1: Remember system all on including sub (not in standby auto switching mode).
2: Stylus on a record but not spinning,
3: Turn volume up to your normal loud position.
4: One hand on the volume control, with the other hand solidly tap the turntable plinth with end of your finger .

And watch your "finger donk" on the TT plinth turn into an ever increasing earthquake with airborn-feedback and continue to get louder and louder as it starts to run away and if not stopped will take out your amp and speakers.

Cheers George