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Woofer pumping possibly due to tube amp when playing vinyl

I am moving this issue  to this forum because of what I discovered this weekend.

I’ve been trying to figure out why I have woofer pumping when I play vinyl, and for the last two weeks I’ve been messing with my vinyl rig trying to figure out what is causing the issue.  The woofer pumping seems to be more prevalent with the vertical up-and-down movements of the tonearm regardless of which turntable is being played. It appears it happens more at the outer edge of the record then the inner grooves.  I assume this is because record is more warped at the outer edges. The woofer pumping happens even in quite passages, so it’s not noise induced vibration affecting the turntable. 

 I have used two different turntables to try to figure this out, one is a pioneer PL 530, and the other is a VPI prime. both with different carts. Also, I have verified that all the carts being used on these turntables work well together with their respective arms.

However, it is not the turntable or cartridges. 

Things I can say for certain, it is not the turntable because I switched turntables with different cartridges to confirm this, and I still get the woofer pumping.  It is not a phono preamp because I’ve switched several phono preamp‘s, solid state and tube, and I still get the woofer pumping. It appears it is the tube amp that may be at cause. It’s the only component left of the chain. 
I have a Audio Research  Classic 60 amp. I got the amp used but it came with a new set of power tubes I don’t recall if I changed the four smaller driver tubes,  I also change the four large capacitors to new capacitors and biased the amp. 
The interesting thing is, with the TT’s I tried, it is the right channel that pumps more than the left channel, regardless of the variety of different cartridges tried, all aligned with AS Smartractor.

To be certain it was limited to vinyl playback, I plugged in a CD player and I do not get the woofer pumping at all. So I have a couple theories (1) the TT is just transferring subsonic frequencies from the records, ALL records I play do this.  Please remember, this is from the two different turntables being used, one a VPI prime belt driven, and the other a pioneer PL 510 Direct DrIve,  or (2) there’s some weird thing going on at the amp that I cannot explain. 
My question is, if there is something going on with the amp could it be a tube issue, or capacitor issue, or a biasing issue.  If so what is the most likely culprit.  Or I guess something else altogether. 
In the end I’m rather tired of chasing this ghost, and I would rather not use a subsonic filter if possible. If I do have to use a subsonic filter I want the most transparent one if such a thing exists. I’ve heard mixed results about the KAB unit. 
last_lemming
last_lemming OP
629 posts
 
Yes I did. No change. 
Also I got the perimeter ring in. Nice piece, keeps the record very flat, but didn’t really change anything. 
I guess it’s a KAB unit unfortunately. 
last_lemming OP
629 posts
 
Hirnd2,

I don’t have a EQ to do what you say. 
thom_at_galibier_design's avatar
thom_at_galibier_design
723 posts
 
Thanks for the responses
to answer some questions:
no sub is in use
my preamp does have mono but didn’t affect the pumping
I will try different speakers to see how that goes.
Tail wagging the dog. Listen to @ millercarbon and others. Work on the front end.

Thom @ Galibier Design
last_lemming OP
629 posts
 
There is probably nothing you can suggest that I haven’t already tried on 3 different TT’s and ended up with the same result. 

not the front end, I’ve eliminated those as variables. Since they are all fine in one room but not the other. 
atmasphere's avatar
atmasphere
11,569 posts
 
You might have a power problem. I saw a situation once where a tube power amplifier drew enough power that when the preamp was on the phono, it was possible for the amp to drain the AC line so far that the preamp started to shut down. That caused it to put out a pulse which caused the amp to shut down a bit- then the line voltage recovered, the preamp made another pulse as a result and the cycle continued- woofers pumping. You could stop it by turning the volume down.


It would only do it with the tube amp that had greater draw and only when on the phono input (which has more gain and so is more sensitive to issues with voltage regulation).

If all the gear works in another room (and hooked up to each other the same way) then I would look into this. It might be as simple as a bad connection on the back of an AC outlet or in the breaker box. A digital voltage meter set on the AC voltage scale and plugged into an outlet on the same line might reveal this problem unless its associated with a particular outlet.
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