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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

Showing 11 responses by atmasphere

atmasphere's avatar
atmasphere
11,646 posts
 
Does it do it without the arm on the LP surface- if you just touch the sylus, can you set it off into pumping?
If no, then the problem is simply that the turntable suspension, in tandem with a mismatch between the arm and cartridge, is the culprit.
atmasphere's avatar
atmasphere
11,646 posts
 
If you run a power cord from a different room (hopefully one not on the same circuit breaker) for the preamp, does it still do it?
atmasphere's avatar
atmasphere
11,646 posts
 
Thanks! Is this affected by the volume control?
atmasphere's avatar
atmasphere
11,646 posts
 
^^ +1 My phono section has bandwidth to 2Hz and no worries about woofer pumping- my system is flat to 20Hz and the woofers are calm unless there are bass notes.


The KAB knocks out low frequencies and part of the reason it sounds different is not only more amplifier power but also phase shift. IMO/IME its better to get a handle on this rather than place a bandaid on the problem. The result will be better sound.


@last_lemming If you had to describe the woofer pumping, how fast was it?
atmasphere's avatar
atmasphere
11,646 posts
 
You might have a power problem. I saw a situation once where a tube power amplifier drew enough power that when the preamp was on the phono, it was possible for the amp to drain the AC line so far that the preamp started to shut down. That caused it to put out a pulse which caused the amp to shut down a bit- then the line voltage recovered, the preamp made another pulse as a result and the cycle continued- woofers pumping. You could stop it by turning the volume down.


It would only do it with the tube amp that had greater draw and only when on the phono input (which has more gain and so is more sensitive to issues with voltage regulation).

If all the gear works in another room (and hooked up to each other the same way) then I would look into this. It might be as simple as a bad connection on the back of an AC outlet or in the breaker box. A digital voltage meter set on the AC voltage scale and plugged into an outlet on the same line might reveal this problem unless its associated with a particular outlet.
atmasphere's avatar
atmasphere
11,646 posts
 
There is but it’s about 8 feet away.
Oddly enough it’s only 2 feet away from the system that doesn’t pump.
Did you try shutting it off anyway? The noise could be getting in through a power cord.
atmasphere's avatar
atmasphere
11,646 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.
atmasphere's avatar
atmasphere
11,646 posts
 
But compatibility isn’t the issue. The same equipment and rack in another room doesn’t cause pumping.  
@last_lemming 

This is an important clue! This means its clearly mechanical feedback between the woofers and the turntable.
atmasphere's avatar
atmasphere
11,646 posts
 
All my carts I have tried fall within the correct EM range.
Some of the carts are suggested by VPI themselves.
This gets tricky- even cartridges suggested by the manufacturer of the arm may not be ideal. This can be because the actual performance of the cartridge (in this case, the compliance value) might actually be considerably different than the spec on paper, the latter of which the manufacturer may have used to make a recommendation without actually having used it.

That is why trying a cartridge with a lower compliance value is a good test of this hypothesis.
atmasphere's avatar
atmasphere
11,646 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.

atmasphere's avatar
atmasphere
11,646 posts
 
@last_lemming 

Since a number of things have been tried on the 'table, I am starting to suspect the phono section might be playing a role. What kind is it?

The fact that its a problem with the turntable and not the CD player rules out the line stage and amplifier entirely.


So it is either the preamp or the turntable, and
the chances of duplicating the issue between to different TT’s and different carts.
-is actually a lot higher than you apparently suspect! BTW woofer pumping has nothing at all to do with whether circuitry is tube or solid state.


I agree that ditching the deer hide platter pad is a good idea. A proper platter pad will damp ringing in the platter and also vibration in the LP itself; deer hide will help with neither. I would think that the deer hide will be really tricky to maintain a uniform thickness- that might actually be the problem right there.

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