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
mijostyn's avatar
mijostyn
8,570 posts
 
Many amps roll off below 20 Hz so you won't see woofers pumping. Your system is doing exactly what it is supposed to do. Moving the turntable won't change a thing. Anybody who uses subwoofers aggressively and plays vinyl will need a subsonic filter. The problem with many rumble filters is that they start rolling off between 30 and 40 Hz so your audible bass is affected. 
Woofer pumping is a big problem. It wastes power and forces your drivers into non linear operation increasing distortion.
The best subsonic filters are digital. My filter starts at 18 Hz and is 60 dB down by 1 Hz. It is totally transparent. If you switch it in and out playing a digital source you can not tell the difference. If you switch it out playing vinyl?? I have 4 12" subwoofers each one driven by 2000 class AB watts, damping factor 500. With some records the drivers will bang against their bump stops!
This is just one advantage in having a digital front end aside from bass management, room control and equalizer functions. 
If you have subwoofers, play vinyl, and have amps that go down to DC you positively, absolutely need a proper subsonic filter. 
last_lemming OP
639 posts
 
Thanks for the responses

to answer some questions:

no sub is in use

my preamp does have mono but didn’t affect the pumping

I will try different speakers to see how that goes. 
atmasphere's avatar
atmasphere
11,841 posts
 
I am assuming this problem only shows up when the stylus is on the LP surface.


I would see if you can try out a cartridge that is a bit less compliant and see if that sorts things out. Woofer pumping is a common complaint if the cantilever has too much compliance for the mass of the arm and cartridge together (along with the position of the counterweight, this contributes to a value known as 'effective mass').

The effective mass, along with the compliance of the cantilever, results in a another value known as 'mechanical resonance'. Ideally this should be between 7-12Hz. If below that, woofer pumping can be an issue! You were asking earlier what the chances could be that two turntables have the same problem and the answer is 'quite high' if no attention was paid to this issue. So its worth it to borrow a cartridge that has lower compliance to see if it gets sorted out.

Ag insider logo xs@2x
cleeds
5,960 posts
 
mijostyn
Many amps roll off below 20 Hz so you won’t see woofers pumping.
Not good ones.
Your system is doing exactly what it is supposed to do. Moving the turntable won’t change a thing. Anybody who uses subwoofers aggressively and plays vinyl will need a subsonic filter ...
Oh no, that’s mistaken. Completely.

I don’t use a subwoofer, but I do use a full-range speaker system that is essentially flat in-room to below 20 hZ. It’s awesome. My phono stage, line stage, and bass amplifier (this is a bi-amped system) are all rated to far below 20 hZ. The system can produce bass that you can’t hear but can only feel.

No rumble filter. No woofer pumping. Ever.
The best subsonic filters are digital.
I think the best subsonic filter is no subsonic filter.
larryrs
132 posts
 
Very good advice from @atmasphere.  Many records are available that have tracks for testing both lateral and vertical resonance of an arm/cartridge combination.  Certainly worth measuring if you haven't already.  
More to discover