Why are my woofers pumping?

The other day, with sunlight direct from the side, I noticed that the woofers in my speakers are pumping in and out, much more than I was aware of, when the stylus is in the groove, even between tracks (no music).  I can see it, even if I don’t hear it. Why does it happen? The woofers behave normally (no pumping) with digital music, and when the stylus it lifted from the groove, so it is not the speakers, amps, preamp or phono stage. 

I’ve read that the typical reason for woofer pumping is that the cartridge / arm resonance is too low.  I tested, with my Hifi News test record, and yes, the lateral test puts the resonance at 7 hz or so – too low (but I’ve seen some doubts about the results from that test record).  It is strange, since the combo I use – Lyra Atlas cartridge and  SME V arm (on a Hanss T-30 player) is supposed to work well. I tried to strip my arm of extras, cleaned the damping trough, etc – but it did not help much.

Anyone has an idea, why it happens, or what to do about it?  

From a subsonic filter manufacturer:

I initially set my Low Frequency Filter switch to flat until I discovered some very amazing facts.There exists a phenomenon called woofer pumping aka woofer excursion. Frequencies below 20Hz are usually not able to be reproduced, and with the exception of synthesizers and pipe organs, are not a wanted part of the audio spectrum. This is especially troublesome with phono systems, since many of the vinyl discs you treasure (or wish to transcribe to CD) will be warped to some degree. Any warp in a vinyl disc will cause large outputs in the subsonic region, typically well below 20Hz. For example, a 33 1/3 RPM album with a single warped section will create a signal in the pickup at 0.55 Hz (33.3 RPM / 60 = 0.555 Hz). This is a signal that will cause significant cone movement, but is undesirable in the extreme. Not only will vented subs be completely unable to handle such a signal linearly, but sealed subs will also be stressed. Large amounts of available power will be wasted trying to reproduce a signal that was never intended to be there in the first place. To be effective, a subsonic filter has to be very steep - this allows all wanted frequencies to get through, and rejects those that will only cause problems. Note that my Citation 1 Pre-Amp's subsonic filter is set at 15Hz. http://sound.westhost.com/project99.htm

It happens regardless of the vinyl record, it seems. It is not mainly a matter of warp or off-centred records.
Your cartridge has a compliance value that is too high for your arm.

You could reduce the effective mass. That can be done with different weights on the counterbalance (a heavier weight, closer to the fulcrum), lower mass arm or a lighter cartridge. If you are using a cartridge shim, I would replace it for one that is lighter. 
move turntable away from speakers -- it may be too close
There’s nothing you can do. It's normal. SME V has already a very low effective mass of 9.5g.

Lyra is a very heavy cartridge at almost 12 grams. It’s compliance is 12 at 100Hz, so probably 21-23 at 10Hz.

Just live with it and when the stylus wears out get something else.

Whatever you do, don't get a subsonic filter, unless of course you want to kill good sound.
Thanks, all!
Atmasphere - you may be right. But Lyra does not warn, and web debate does not complain, using the Atlas on the SME V - so i wonder.
Czarivey - good suggestion, but I doubt speakers or airborn feedback is the cause. Sounds (looks) much more "physical".
Invictus - yes, I see what you mean, but investigating more, using my eyes, plus my finger on the woofer cone, and my ears - my feeling is, this pumping has messed up my musical image. The SME V has an effective mass of 10.5 g I think. The Atlas has a compliance of 12. The calculators I’ve tried pushes this into ca ok "green" 10 hz territorry. Am I overlooking something? Is the Atlas really ca 22?

Atmasphere - you may be right. But Lyra does not warn, and web debate does not complain, using the Atlas on the SME V - so i wonder.
It might be that some of those debaters don't have the bottom end bandwidth in their systems that yours has.

I went from the SME5 to the Triplanar and that helped get rid of that problem in my system. The SME5 seemed like it was a higher mass arm than the Triplanar. 
It is a long-term discussion -
Atmasphere, isn’t your Triplanar arm mass higher than the SME V?
I should get the arm mass down, to get the resonance frequency up - true?
Increasing the arm mass is not difficult, decreasing it is the trick ;-)
I agree with @atmasphere that cartridge compliance is almost certainly too high, although placing the turntable too close to your woofers may exacerbate the problem. Short of replacing the cartridge and/or counterweight, you might also see if you can lessen the problem with damping. You write that you "tried to strip my arm of extras, cleaned the damping trough," so it’s not clear that you’re using any damping at all. Is that correct?
It might be that some of those debaters don’t have the bottom end bandwidth in their systems that yours has.
That’s possible. It’s also possible that the debaters have absolutely no experience with the arm, or with your arm/cartridge combo. There are many self-proclaimed vinyl "experts" on the web who have no idea what they’re talking about.
Thanks Cleeds - yes, I just tried with and without oil in the fluid damping trough on the arm. Made no difference.
I am happy with everything this combo does, except that it overarches in the low region, takes in too much. What about a simple cut off below 10 hz. Maybe a DIY. I use XLR cables. Suggestions, anyone?
I am happy with everything this combo does, except that it overarches in the low region
That's rather like, "Other than that, Mrs. Lincoln, how did you like the play?"

It sounds like the cartridge compliance is just too high.

Thanks Cleeds, but I don't agree. Please prove the case. Why does the arm kill the cartridge?
From the A-gon opinions so far, here, such examples are not very interesting. It seems that the SME V can work OK with the Atlas, but it is not the ideal arm - ? I will look for other cart / arm combinations, when my current one runs out, and I have the money. But for now, I look for a fix.
Dear @o_holter : Seems to me that you don’t have a real problem between your SME and the Lyra cartridge in the resonance frequency, you are safe there.

What " alternatives " left other than that. Thinking " loud " some things could be stay happening:

maybe to many playing hours in that cartridge that in some way affected the cartridge suspension or stylus tip or both, only for you can be sure re-check all the tonearm/cartridge set up parameters: VTF, VTA, overhang, offset angle, etc, etc., if you have a different platter mat you can try it and see what happens, same with the use of a platter clamp and if you are not using it then try one, could exist a very low bass oscilations developed in the phono stage so browse from somewhere and make a change of phono stage only for testing, you can try too to put some kind of damping material as bluetack between the cartridge top plate and the tonearm headshell, you can damp the SME arm wand with a elastic thread around t in helicoidal way ( in the past Sumiko marketed this kind of trap to damps the arm wands and made it a great improvement always. They used a ligthly elastic material. ).

Could be another reasons that explain such behavior? could be but rigth now those are some things you have to check and see what happen.

I assume that you did not any change in your system/roo but the same as always only that you do not noted before, rigth?

Regards and enjoy the MUSIC NOT DISTORTIONS,

cut off below 10hz? as invictus said that will degrades the cartridge signal and in the other side you do not know at which bass frequency is the problem, seems to me more lower than 10 hz but as you I can't say for sure.

Thanks, Raul. I will test some of your suggetions - platter mat - and report back. But like I said before, it seems very basically "physical" - it happens before eventual mechanical turntable etc problems.
@o_holter : problem is that you just noted it and could be many thing. Even that speakers can't reproduce the frequency the woofer movements are affecting the quality level performance of what you are listening.

Even a mistmatch impedances between phono stage and line stage could be ( for whatever reason. ) the source. The electronic very low bass oscilations are more frequently that what we can imagine.

You have to make several tests about because exist no rules to make a sure diagnosis about.

Thanks Cleeds, but I don't agree. Please prove the case. Why does the arm kill the cartridge?
The SME V is a terrific arm, but your woofer pumping problem simply suggests you've mounted the wrong phono cartridge to it. There's no reason to suffer such a problem, imo, and using a subsonic filter is treating the symptom rather than the disease.

Question for @o_holter : Did you buy this cartridge used?
If so, all bets are off. You can't be exactly sure of what you have.

Raul's suggestion that the cantilever suspension is failing could be an explanation, but the problem I have with that is the cartridge must be pretty new so this seems really unlikely.

I looked at the specs of the ARC used in the review; it cuts off at 10Hz. Your preamp, if still the Io, is only specced to 20Hz (at which point its within 0.25db, suggesting that it can go down considerably further). So its an unknown as to whether that's an influence. Your amps are full power to 1 Hz. I use similar amps in my system at home, but I don't get the woofer pumping, although that was a problem when using the SME5 and has not come back while using the Triplanar (which I see was used in the article you linked, so this problem may not have shown up).

A filter will introduce phase shift, and in a full range system such as yours, will be audible as less bass impact. So its probably best to solve this with elegance rather than brute force.
@o_holter Does this happen when the woofer and other equipment is not in the sun?
Same problem on 3 different Turntables. As a last resort, I bought a KAB rumble filter which I run via the tape loop. I do not notice any less bass and my system really swings. The filter even uses audiophile parts in it. New it was 179.00 but I saw one on here a couple of weeks ago for around 100.00 That, is a good deal. Regardless at what others will tell you, in my system it did not cut the quality of the bass or the deep bass. I can rattle the windows playing vinyl if I want.  The sun has absolutely nothing to do with it.

Ok, the sun was a herring. I thought that the temp might cause a solder break to open a fraction more. It was just a thought.

I've heard of a rumble filter but I have no idea how it works.

These mismatches exist and you’ll never figure out why, nor will you ever fix it. Just enjoy the music. SME V is arguably the best tonearm in the world ever made. And Lyra makes superb high end MC cartridges, even if I’m not the biggest fan.

Rumble filters not only ruin the bass, but suck the life out of the entire system.
Check the turntable bearing?
Subsonic/rumble filters are crap! You have to use a combination of things 1. record clamp 2. Cart/tonearm compliance 3. Isolation 4.overall setup... I still get woofer pumping but not nearly to the extent it was happening before. I find that using a turntable with a great clamping system (not just a puck or weight) helps a lot to avoid these effects and having the turntable on a piece of granite will be a big plus in helping kill the pumping. Also, finding the right cart/tonearm combo makes all the difference as well. At this level things really need to be in proper order (turntable setup) because things are so sensitive double check table for level, VTF, VTA, ect... 

Matt M

Set the volume at the lowest setting at which the woofers pump with the platter spinning and the stylus in the groove. Place the arm at rest. Does the pumping stop or continue? If the woofer pumps with the arm at rest (at a volume at which you might play music), the cause would appear to be acoustic breakthrough/feed back loop: TT/arm/cartridge > amp > speakers > air > TT/arm/cartridge > etc). The solution is to minimize acoustic breakthrough via one or more of the following:

Increase TT to speaker distance

Place TT and speakers in different rooms
Increase TT mechanical isolation: if TT couples to a raised wood floor, site the TT on a shelf mounted to wall studs  
Change TT from unsuspended to suspended (I prefer unsuspended TTs).
Change to a TT that better resists acoustic breakthrough (Sota's old Saphire and Star both may have set the standard for being impervious to feedback, but Sota motors are small and low cost, and the TTs made audible W&F....I use a 68 lb TT: Empire 208 motor/platter/bearing on a 1.5” solid alloy custom plinth ala the one Atma-Sphere used to make and sell).

It appears other users reported good results with your arm/cartridge pairing.

I suspect the pumping would be visually similar in your application, even if you swapped speakers (as long as all were reflex loaded). The reason is that reflex loaded woofers (mid bass in your case) unload below the port resonance, and for all full range speakers the pumping resonance is well below the port tuning resonance frequency. (Even if the pumping looked similar between 2 different speakers, pumping likely audibly degrades one speaker more than another, based on many variables.)

But suppose 2 persons employ the exact same arm/cartridge: person A's preamp/amp cuts off very low and makes high power in the bass (your OTL amps make more power @ 16 Ohm than 8 Ohm, the opposite of typical SS....also I don't know the speaker's impedance at pumping resonance); person B's preamp/power amp cuts off much higher and has minimal bass power. Person B's results may be fine, with little to no pumping, while person A's woofer pumping may audibly degrade performance. This could explain why your pumping is worse than another system with the same arm/cartridge.

Unfortunately I lost the link, but in the 70s IIRC, a European PhD. (I think a major European company like Bruel and Kjaer employed him) did a scientific paper on the subject of the ideal resonance range. He concluded that the ideal resonance frequency range is significantly higher than usually recommended. I use a Pioneer strain gauge cartridge, high compliance and very heavy. When I lowered the Rega RB300 arm resonance with a lighter counter weight, performance audibly improved by huge margin.

Long term wise a different arm/cartridge pairing may be the best solution. My strain gauge needs a true low mass arm, so I purchased a used Audio Technica AT-1100 with two wands. I shall add mass to one wand for use with a mono cartridge.

Your SMEV is in another universe v. my AT arm. The AT arm's effective mass is only about 7g. If/when finances allow, I plan to upgrade to the Moerch DP arm, which has 4 different wands of various mass from about 4g to 12g.

I always loved the looks of the SMEV, and the pro audio reviews were effusive in their praise of its performance. I'd buy one if it fit my needs.  

IMHO, you need a filter, or (cough), an eq to filter out anything below 15 hz. Some of it could be acoustical feedback.  I thinks it’s much more simple, than a mismatch or incorrect setup of tone arm/equipment.
I am no expert but I had the same problem with a VPI Prime Signature
and a very sensitive Van den Hul cartridge. I moved the cartridge to my
other VPI Prime Signature (identical) and the problem stopped. Turned out it was a acoustic feedback loop being caused by low level sound waves bouncing off the corner of the room.  VPI turntables are well isolated but the VDH cartridge is very sensitive. So I agree with those who suggest isolating the turntable. That said, some cartridge tonearm
combinations don't work, usually low mass cartridges on high mass arms. 

Thanks, all! Great to get so much expertise input!

Cartridge is probably OK, not worn, no sign of wear, or mistracking. Like I said, it is not the Io phono stage, since when the stylus is lifted from the groove, the woofers stop pumping. I have tried a platter mat, and different weights – no difference.  Mechanical problems? Player is level, on a solid stone rack. Testing with sthetoscope and fingers: very silent. I do find that the shaft that holds the spindle could be tightened a bit, but I don’t think this relates to the pumping. Also, this is clearly not related to airborne feedback, position of speakers, damping, etc. Either, the woofers pump (stylus in the groove), or they don’t.  It happens on all kinds of records, is not dependent on warps or record problems.

My new diagnosis is this.

1) Like many of you have said, the Lyra Atlas /SME V combo can be non-optimal – the resonance is too low. Maybe, those who don’t hear problems, have a less resolving system at low Herz, or a subsonic filter. I think I have solved the numbers mystery. The Atlas specs say: “Compliance 12 x 10-6cm/dyne at 100Hz”. But the calculators I have found (e g at Vinylengine) measure compliance at 10Hz. Noone seems to know the exact conversion, but a rule of thumb is to multiply the 100Hz value with 1.5 or 2 to get the approximate 10Hz value. This means that the Atlas compliance is in the region 20 to 24 (not 12). Using this value in the calculators, I do get a too low resonance for the combo, around 7.5 Hz. This fits quite well with my Hifi News record lateral test result (6-7Hz). Since obviously people have used Lyra’s with similar compliance to the Atlas and SME V arms to great benefit, the correct term is probably “borderline low”. It can be good enough, or not, depending on the system.  

2) With this “borderline low” situation, the cart/arm picks up too much of what happens down in the subsonic region. I tested with a record at the end of the runout groove, just now. The usual situation where the LP is still going round at the end, with an audible pop for each revolution. The pop is clearly audible. The pumping is only or mainly visual. I think they interfer with each other (indicating that the pumping is no good for the sound). I also found that there is a rythm to the pumping. A pattern is repeated for each revolution, so if I change platter speed from 33 to 45 rpm, it happens faster. My conclusion: The cartridge picks up player rumble. This is not because the player is bad or poorly tuned (the Hanss T30 has received a lot of praise for its silent motors, combined magnetic/ceramic spindle system, speed stability, “inflappable” quality etc) it is just what you get when you turn on a flashlight or microphone down low, in the 5-7Hz region.  Assuming that the low resonance acts like a microphone (which fits my testing).

Agreements – or not? Am I overlooking something?

So – what to do?

Some of you say a filter works, others that it doesn’t. For me, with a great cart and arm, prone to run many years ahead, it could be worth trying. Other options (change cart, arm) are far more expensive. Suggestions welcome. There are small XLR filters, but the ones I’ve seen on the net are for microphone use, with too high cutoffs, 100 or 50Hz.

Interesting post as I had a similar post about a month ago regarding the compliance at 100 hz and I received no replies.  Its a good question.  A very good question.  Someone at Lyra should respond to explain this as I am very interested in understanding this better.  I noticed a similar thing, not that my woofers were pumping, but I heard what I believed to be a compliance issue.  It is better now that the  cartridge is broken in but sometimes I do ask myself this question as well.  Maybe Lyras are made for lighter arms if the compliance is so high at 10Hz. 
@o_holter A simple way to decrease the compliance of the cartridge would be to load it. I would try 50-100 ohms and see how that works out.

Its not a sure bet- if you load the cartridge too low, its output will decrease, and in turn you phono preamp noise will be more audible. But its worth a try.

Damping would probably make matters worse; I would run it without damping and remove the little bit that runs in the damping trough to reduce mass, even if its only a little bit.
@invictus005 To which part do you address the 'huh'?
@atmasphere All of it...
OK... what do you want to know?
O_Holter, while it indeed sounds like the problem is a consequence of the arm/cartridge resonant frequency being too low, I’ve been thinking about what might be exciting that resonance, since based on what you’ve said it seems that the excitation is probably unrelated to record warps. And the one thing that occurs to me, given the unusual design of the turntable’s drive mechanism (comprising six belts, three of them driven by what is apparently a synchronous motor on one side of the table, and three of them driven at a different height by a similar motor on the other side of the table), is that the platter might be being driven in a slightly uneven and/or not perfectly level manner. Perhaps simply due to the condition of the drive belts differing slightly between the two sides.

And I note from your system description thread that the table appears to be around five years old. Perhaps all that is needed to resolve the problem is a new set of belts?

-- Al

Dear @o_holter : According your self research looks like the rpoblem is developed by the TT and not a mistmatch between cartridge/tonearm because even at 100hz the Atlat compliance and effective mass puts the resonat frequency in a " solid " 8hz.

The cartridge is a very sensitive " microphone "/transducer and it's picking up " something that is happening somewhere in the TT.

Normally when  a some kind of resonance/vibration are exiting/coincide with the cartridge/ tonearm resonance frequency in between the pick up jumps more than make a noise.

Before you go for the filter try to " figure " what could be happens in your TT. You are the one that know it, even contact the TT manufacturer and ask for its advice.

Regards and enjoy the MUSIC NOT DISTORTIONS,
Your problem is most likely a combination of ununiform belt thickness, not precise pulleys, motor rumble, not precise bearing. They all combine and create a mechanical shimmer in the turntable's suspension. 

While playing the runout groove and watching the woofers move in and out. Gently, but firmly place your hands on the plinth and try to very carefully hold it in place. The woofers should move in and out less.
Still even though it still falls within the 8hz range, I believe the ideal range would be closer to 10hz.  so if you buy a cartridge that you think has a compliance of 12 and it is really closer to between 16 and eighteen, i would think that would be audible at some frequencies which could be bothersome for some people.  its kind of deceiving as I did not even notice the whole 100 hertz thing until after I bought my cartridge.  It still sounds good but it is not what I thought I was getting.  for instance when I bought a benz cartridge and its compliance was 16, it was 16.
tzh21y - yes I think the same. Maybe even small things help, getting the resonance up. Stripping the arm of all extra mass and changing the counterweight position, like Atmasphere suggested.
Invictus, Almarg - I don’t think the player is the problem, behaves much better than my former VPI. The plinth is dead stable as it is. Belts - maybe new ones would be better, but this is not the main cause.
Somehow, the pumping has decreased a bit over the last days. Not sure which of my modifications that made the change.
The pumping is now very evident when I turn the volume up to 92-96 db from the listener position - measured when playing music. Going down to 88-90, where I usually listen, it is not so notable. I must test this more, trying to find "silent" vinyl grooves.
Atmasphere - I was not aware that loading could influence the resonance - ? I load the Atlas at 475 Ohm, but could go down to 100, have not tried yet.

Why don't you try what I posted...
Invictus005: I've tried your suggestion now, holding the plinth, but it makes no difference. This is a very heavy player (83 lbs). I used the runout on the Hifi News test record. And noticed, once more, that the woofer pumping is much reduced, compared to some days ago. In fact, it now looks/feels more like normal vibrations. And this is with the volume very loud (95+ db when playing music). So, where did the pumping go? I have a prolapsis so testing takes a bit of time. I wish I could tell you more exact what has caused the reduction of the problem. Besides reducing the effective mass, I did take off the platter, checked the spindle and moved the steel ball a little.

I also discovered that, indeed, "silent" record grooves are not the same. I have a UK original of Pink Floyd: Meddle, that plays amazing, especially side B (Echoes), with "HTM" in the deadwax, which means Harry T Moss "cutter extraordinaire at EMI UK" from what I read. In the silent-to-quiet opening of Echoes, the woofers pump a lot (on high volume). Is it a problem? Rather, I get the impression, this was intended by Mr Moss, to get the absolute best from the recording. As the music gets louder, I don't see the pumping (since the musical energy now grabs the woofers), although it may be there, in the background. This is what I suspect, and the reason I wanted to improve the situation in the first place. I think that this relates to a more "tense" or "disturbed" sound, and also, to a bit of break-up of the woofers at high volume (in sum - creating more listening fatigue). Btw the woofers are Acoustic Elegance TD10X (four of them in my system).

Testing again, with the HiFi News record side B band 6: Unmodulated groove (check residual system noise). Not much pumping even at unrealistic high volume. Even this track is not fully silent (what record is?) and the cone movement is in line with what I hear, indicating - I think - that indeed, the cartridge/arm combo has become less over-eager down at 5-6 Hz. I tested the runout on some other high quality records also - MFSL, ECM - same result.

There must be other Lyra cartridge / SME V owners out there, who have or don't have woofer pumping - ? Would be nice to hear from you! And maybe J Carr from Lyra could give a comment?

Atmasphere's advice reminded me of the old trick with the SME V to reduce effective mass: put the spring-loaded weight scale at zero, and then adjust the counterweight closer to the bearing of the arm. I use an electronic weight to get it exact at 1.72 g.

Based on Atmasphere's advice, I also tried higher loading, going from 475 ohm to 121 ohm (not so easy on the Io, changing a jumper at the back). Result? Musicality: great. "Echoes" sounds a bit sweeter, more mellow. I realize, I am moved by the music - always a good sign. Is it also a bit duller, rolled off, or contracted? Not sure. Maybe a little. I will have to try the middle setting (243 ohm). Testing with the Hifi news record, I did not find any change in the resonance frequency, it is still down at ca 7.5Hz.

More precisely: I can hear the test tone starting to quiver at 8Hz, increasing down to 7Hz, and then I can see the cantilever vibrating badly at 7-6Hz. So the effect of my various measures to raise the resonance seems rather small, and yet, the woofers have mainly stopped pumping. Why? Something else I did? Just changing the position of the player and spindle, a little? Is it the position of the sun (as was suggested)? The collective psyche of Audiogon members? I wish I could report some more hard facts. But whatever the case, I am mainly happy with the outcome. Even with NOS tubes in the first gain stage, the Io's noise level is mostly below the average groove noise level.  

OP. This is all bunk. Just enjoy the music. 
Like I said in a earlier post, just buy the KAB rumble filter and be done with it!  I tried everything mentioned in this thread at one time or another and only the KAB filter worked with no loss in bass quality or quantity.  I am using it with a VPT Prime and a ZU/Denon Dl103mc.  My woofers would oscilate so much I thought they were going to come right out of the cabinets.  With the KAB, nothing, nada and perfect pitched
Based on Atmasphere's advice, I also tried higher loading, going from 475 ohm to 121 ohm (not so easy on the Io, changing a jumper at the back). Result? Musicality: great. "Echoes" sounds a bit sweeter, more mellow. I realize, I am moved by the music - always a good sign. Is it also a bit duller, rolled off, or contracted? Not sure. Maybe a little. I will have to try the middle setting (243 ohm). Testing with the Hifi news record, I did not find any change in the resonance frequency, it is still down at ca 7.5Hz.
Loading should not affect the tonality of the cartridge, as essentially the loading is to prevent a resonance at very high frequencies from occurring by detuning it. If it made for an improvement, it means that the phono section is sensitive to RFI at its input and may have stability problems (but not the sort that cause woofer pumping).

In an ideal situation, the cartridge should be loaded by 47K. With low load resistances (like 100 ohms) the cartridge has to do more work, and that energy coming from the stylus motion means that the cantilever has to be stiffer as well. JCarr and I talked about this at Munich a few years ago.

Now you mentioned that you examined the platter bearing- did you lubricate it? If the platter bearing was dry, the simple act of removing the platter and reinstalling it may have gotten enough lubricant in place to result in the reduced woofer pumping. So the arm and cartridge combo not being ideal might be a complete red herring.
@o_holter Reading over these posts I'd lean toward motor, pulley or bearing as the source of the problem.  By way of example, a couple years ago I noticed excessive woofer pumping in my speakers.  It was extreme to the point where I could hear chugging from my subwoofer.  I have a VPI HW-19 Mark IV with a very early SAMA.  The early SAMAs came with a flywheel that was a large stainless steel washer that just slipped over the motor shaft.  Upon examination I noticed that this "flywheel" was wobbling while the motor was running.  I removed the flywheel and the problem was solved.  I later learned that VPI eventually realized the flywheel was causing more problems than benefit and discontinued using it.

Since you observed much less pumping after removing your platter it sounds like either your platter was out of balance on the bearing or the bearing was not properly seated.  I would clean the bearing shaft with long qtips and reoil the bearing shaft with a high quality oil.  I use sewing machine oil.  Second, I'd examine the pulleys and motor shaft for any wobble.