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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
cakyol's avatar
cakyol
940 posts
 
This issue does not have anything to do with a tube amplifier.

You need a better turntable and a subsonic/rumble filter. I am surprised you see it on a VPI however since it is usually a better turntable.

The rumble usually (but not necessarily only) comes from the main bearing of the turntable and is at very low frequencies (8 - 20 Hz). You can sometimes hear it and more often actually see it (as you have in your woofer).

It is the noise generated from the bearing shaft & the sleeve grinding against each other. No matter how excellent and/or mirror polished the main bearing may be, at the end of the day, they are still two separate pieces of material grinding against each other. You should see it under an electron microscope and you will understand :-)

Typically good turntables have a rumble figure of less than about -75 db or so (quiet). Excellent ones reach down to -82db ish (very quiet). You can reduce it but never eliminate it completely. It becomes pretty audible and a nuisance at around -70db or higher (give or take a few dbs, not an exact science).

Limitations of analog playback :-)

ditusa's avatar
ditusa
1,907 posts
 
@ last_lemming, Take a look at a walker audio crystal reference record clamp. It is a great clamp. :-)
larryrs
132 posts
 
@ last_lemming, have you measured the vibration at the turntable platter directly?  I have an app on my phone that will measure vibration on a surface in the X-, Y-, and Z-axes.  It might be instructive to get some sense of the magnitude of any disturbances that might be causing the woofer pumping.  It can also be useful to determine if any vibrations might be cyclical in nature.  This could be the case if an appliance (e.g., a refrigerator, air conditioner, heating plant) is the source of the problem.  Have you measured any vibration on the walls or the floor of the room, either with your hand or using some sort of instrument?  Seems like you've exhausted pretty much all of the more system-specific possibilities so maybe it's worth looking for another environmental cause.
buldum
2 posts
 
I agree with larrys. One time my turntable's lid was tilted and  vibrating which caused such woofer pumping. (I learned my lesson). It may be a mechanical vibration in the room around 1-20 Hz range and stylus is picking it up. 
last_lemming OP
639 posts
 
Larryrs,

I have considered this but the nearest appliance is a gas range opposite Side of the wall. 
If there is a phone app I’ll certainly give it a try. Got nothing to lose. 
One thing I don’t understand is the speakers go down to 32hz, but sub-Sonics can be far lower, so how do the speakers reproduce below there operable range with such amplitude as to move the woofer in and out 1/4” or more, when my strongest bass note I can get when turned up only moves the woofer 1/16”. 
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