2. amps-preamps
  3. 159881-46

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
638 posts
 
definitely don’t agree with the “need a better table than the ones listed” comment. All 3 of these tables have been in another system with No issues.  

Today I brought my other system in the same room as the offending system. Mind you the other system with same record doesn’t pump the woofers. But in this room, guess what, pumps the woofers. 

And, oh, when I bring the original offending TT and cart to the room with no issues, guess what, NO pumping. 

And don’t forget. I get pumping in the quiet passages in all things I’ve tried. 
So now a total of 3 tone arms, 5 carts, 3 surfaces to place TT on, 3 phono preamps, 3 amps, 3 preamps, 3 different outlets through out the house, 3 sets of speakers, 2 different alignment styles, and untold number of combinations of the above not to mention all manner of alignment adjustment have brought zero differences in the amount of woofer excursion, accept for when the mono switch was thrown, which did lower it about 30% (best guess). 

Here is what I do know. 
1. It happens with any turntable in this room regardless of all things done above to alleviate it. 
2. CDs don’t cause any pumping. 
3. The pumping isn’t caused by speakers resonating the TT, since it happens on quiet passages and at lower volume levels. 

4. regardless of placement In room or surface: concrete, rack or carpet I still get pumping. 
5. None of equipment, including any of three TT’s, amp pump in the other room. 
So what does this mean? Well, there must be some type of EMI or similar coming from something in the walls or in this area of the house interfering with the TT set up. Though the only thing I can think of if the oven/range on the opposite side of the wall.

I might be at the KAB point, unless I can figure out what’s the root cause.  

psag
518 posts
 
I understand that you’ve tried two amps, but problem is an incompatibility between your chosen speakers and your chosen amps.  Review the specifications of your components and make sure that the numbers work in theory. If you value your amps more, then purchase a more compatible speaker. If you value your speakers more, then purchase a more compatible amplifier. Either way, problem solved.
last_lemming OP
638 posts
 
Psag,

Thanks. But compatibility isn’t the issue. The same equipment and rack in another room doesn’t cause pumping.  
ditusa's avatar
ditusa
1,883 posts
 
@ last_lemming, Turn off the oven/range breaker at the panel.  Then play the audio rig. To see if you still have woofer pumping. Mike :-)
mtemur
11 posts
 
if you moved all the equipment to another room and the problem is solved then check AC line and grounding. also check AC polarity on all equipment (remote possibility).

still if you can not find any solution then use subsonic filter
or
if sound quality degradation caused by subsonic filter really matters to you then get better turntable, tonearm, cartridge and phono preamp.
More to discover