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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
atmasphere's avatar
atmasphere
11,633 posts
 
All my carts I have tried fall within the correct EM range.
Some of the carts are suggested by VPI themselves.
This gets tricky- even cartridges suggested by the manufacturer of the arm may not be ideal. This can be because the actual performance of the cartridge (in this case, the compliance value) might actually be considerably different than the spec on paper, the latter of which the manufacturer may have used to make a recommendation without actually having used it.

That is why trying a cartridge with a lower compliance value is a good test of this hypothesis.
paulleellama
5 posts
 
One thing I do know is that a deer hide mat is not an issue for the problem. I use one in combination with a center weight and extremely satisfied with results.  I was wondering if the VTA of the cartridge was evaluated or tweaked, I do know a rake greater than 93% can cause audible issues. You have to use a digital microscope to view the position of tip/cantilever to verify.  The manufacturer doesn't always build the stylus to the specifications they advertise. 
larryrs
132 posts
 
@ last_lemming, What cartridge(s) are you using with the Prime?  It's a good chance that someone reading this thread may have the same combination and they can check to see if they are having a similar issue.
unreceivedogma's avatar
unreceivedogma
916 posts
 
I'm with Mr Miller. Clamp it down. I also have the cabinet bolted to a brick wall that my VPI HW MK IV is sitting on.

I have a Velodyne 15" sub with it's pwn power supply, and use Altec 604Cs. 

No pumping unless I dial up the sub volume, which is not desirable in any event.

tdybare1
13 posts
 
Last_lemming I had the same problem a few years ago. I had the same turntable for years and never had a woofer problem. I then moved and in my new room the woofers started pumping. I remember this problem back in the 70’s and 80’s and thought turntables built today couldn’t possibly have this problem. It’s the room. Some vibration is getting into the turntable to cause the woofer pumping. That’s why, even though you placed the turntable on the concrete floor the turntable was still causing woofer pumping. A concrete floor still gets vibrations from the earth. I tried the same thing. I solved the problem with the Symposium Acoustics Segue ISO turntable platform. They can be bought through Acoustic Sounds. There are two types of these platforms one for lower weight turntables ( I think up to 40lbs) and one for heavier weight turntables ( up to 80 lbs). This will solve your problem. 
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