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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
stereo5's avatar
stereo5
6,539 posts
 
I have the KAB Rumble Filter and it is amazing. No sound degradation whatsoever. I have a/b back and forth probably close to 100 times in the 7 years I have owned it and once the levels have been carefully matched which I can do on my Mac C2500 preamp, there is zero difference. The 7 or 8 friends that have heard it concur with me.

In my system due to the location of the Turntable in conjunction with the speakers, It is one of 2 solutions. The other is to stop playing vinyl.
ditusa's avatar
ditusa
1,988 posts
 
I concur, with stereo5. Or move the turntable to a different room. :-)
millercarbon's avatar
millercarbon
12,531 posts
 
Lord. Of course its the turntable. Specifically, its the way the record is clamped to the platter. ALL records, if you just plop them down, are going to produce some degree of the very low frequency energy that you see as woofer pumping.

When I play records, any volume, there is plenty of bass and no woofer pumping. Without filters. Horrible idea! Look at my system. Please. Took the time to post the pics for a reason: so everyone can learn. Study, observe, and learn. Please.

https://systems.audiogon.com/systems/8367
Look close at the platter. Notice the black ring around the spindle? Looks like a washer. Its not. Its carbon fiber. Its hard to take a picture from an angle that shows every detail clearly so you have to really study it. Which you should do! Totally worth the time. See how thick the washer is? A record placed on this is held just very slightly higher than the surface of the platter.

If played like this, or if any record was played on this same table without the washer, just sitting on the platter, there would be all kinds of woofer pumping. Because at the scale of amplification we use even near invisible amounts of vertical motion at the record translate into a totally obvious pumping at the woofers. The fact you mention being able to see the tone arm move AT ALL tells me you’re not even close to doing it right.

So the next step after placing the record on the washer that holds it too high is to clamp it down. My record clamp is dished out inside, so as its clamped down it presses the record down onto the platter from the outside edge in. Fully clamped the record is absolutely flat on the platter. Its clamped so flat that when the clamp is released its like its been suctioned down onto the platter, which you can tell because when the clamp is released the records stay down for a second until air comes in and it pops up.

This is what you want. Its not your amp. Forget about that. Waste of time. Don’t move your table. Its embarrassing how far off track some of these ideas are. Look for a good clamping system. Clamp. Not weight. Clamp.
last_lemming OP
639 posts
 
I moved both TT’s - all over the place.  Not change at all and that’s spiked through to the concrete floor. 

Miller,

I can’t discount your thoughts about the clamp, but how would this affect the outer edge of the record where there is no clamp. 
I use a heavy record weight - which I know you say is no good - but it firmly holds the record onto the deer hide mat. 
I’ve also tried several matts to no avail. 
You’re definitely right about one thing, it’s not the amp, I just pulled out my old CJ MF2100, and I get it there too. So there goes that theory. 

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