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
639 posts
 
No fireplace in the room where the pumping occurred, but ironically in the room that does have a fireplace it doesn’t pump. 
Stringreen,

not sure I understand the question but the 4 surfaces I have directly coupled the TT to are:

concrete floorRigid stereo rack
heavy wood cabinet
on carpet

all of these surfaces produced the pumping exactly the same with 3 different TT’s and 5 carts. Also all these TT’s were moved around the room having the pumping issue and the pumping remained the same. 

In the other room where I don’t have pumping none of the 3 TT’s pump. 
So frustrating!
mijostyn's avatar
mijostyn
8,570 posts
 
Cleeds, the problem is your room is not flat down to 20Hz. It is easier and safer to correct a subwoofer than a full range system without overloading either the speaker or the amp. 

Last Lemming, just for fun try moving your rack three feet. Changing the position of the turntable relative to the nodes in the room might have an effect if it is feedback. Feedback will tend to be sustained and limited to a small band of frequencies whereas the woofer reproducing record warps and irregularities will be random. 
mijostyn's avatar
mijostyn
8,570 posts
 
I guess I should read more carefully. You have already done that.
Look at the pumping, irregular or confined to a certain frequency. 
If it is irregular we are back to subwoofer, filters and caps.

My subwoofers are corrected which means certain frequencies are boosted up to 6 dB. If I delete the subsonic filter from the program it ia mass pandemonium. It looks like the drivers want to jump right out of the cabinet. It is just inherent in vinyl if you have a good system capable of reproducing deep bass.
Ag insider logo xs@2x
cleeds
6,039 posts
 
mijostyn
Cleeds, the problem is your room is not flat down to 20Hz.
My full-range speaker system is essentially flat in-room to below 20 hZ. It’s odd that you believe otherwise without knowing anything at all about my room.
It is easier and safer to correct a subwoofer than a full range system without overloading either the speaker or the amp.
That depends on so-ooo many variables. I’ve used my speaker system safely for years with no issues.
... If I delete the subsonic filter from the program it ia mass pandemonium. It looks like the drivers want to jump right out of the cabinet. It is just inherent in vinyl if you have a good system capable of reproducing deep bass.
Oh no, that’s not inherent to LP at all. It’s true that woofer pumping can be common with improper setup or inferior equipment, but it’s not inherent to LP playback.

I have no subsonic filter at all in my system. The bass goes down below audibility to frequencies that can only be felt, not heard. No woofer pumping. Ever.
atmasphere's avatar
atmasphere
11,979 posts
 
Again, on quiet passages. It’s not a physical manifestation, it’s electrical.
@last_lemming  Is there any sort of digital, bluetooth or other device that can make RFI near the phono preamp or phono? I've seen cell phones induce woofer pumping as well as defective digital gear.
More to discover