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
 
Sorry guys.  It’s NOT THE TT’s. All three do it on all different rack types. There is no way you get the exact same results on three different TT’s, sorry, that’s not the case here. 
Is not induced by the music. It happens on quiet passages. No music to cause pumping. 
I believe it’s EMI or similar. 
That being the case how can I track that down. 
Remember in one room the same TT and racks reproduce pumping and in the other, with all three TT and in the same rack I don’t get the pumping. Again, on quiet passages. It’s not a physical manifestation, it’s electrical. 
But thank you for your responses. 
tablejockey
3,961 posts
 
What I'd like to know is-members who have their table setup dialed in,  no rumble filter and use sub(s).

By the reports of some, you can actually play any LP, CRANK the volume, and you have ZERO woofer pump? 
larryrs
132 posts
 
@last_lemming, I'm having a difficult time in reconciling the findings with the EMI hypothesis.  That the pumping only occurs with a turntable, is worst at the periphery of the record, and is reduced by 30% when the preamp is put into mono mode all indicate to me that it is a mechanical resonance issue.  Maybe the best thing might be to start with the basics and go from there.  If I remember correctly, the table you normally use in the room is a VPI Prime.  I would start with that and put it on the shelf without any added isolation platforms or aftermarket feet, etc. and get a sense of the resonance level.  I would then try what I think will be most effective mechanical remedy for reducing the pumping and that would be a periphery ring in concert with a record weight.  The VPI ring, at least, is designed to work in concert with a weight not with a clamp (as @mytthor mentioned),  If that eliminates the pumping, great.  If it diminishes it but doesn't eliminate it, I would then try an isolation platform or a foot upgrade and see where that gets you.  If these mechanical remedies don't cure the problem, then the next step would be wall mounting.  Given that the pumping is worse in the right speaker, I would put the wall mount over to the left.  If all of those mechanical remedies don't solve the problem, then I think the only alternative is to go with a subsonic filter.  BTW, I had suggested in an earlier post that you try to measure the vibration directly.  I have an app on my iPhone called VibSensor that does that.  I'm not sure if it's sensitive enough to pick up vibration on your platter but it would be worth a try.
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cleeds
6,038 posts
 
tablejockey
... members who have their table setup dialed in, no rumble filter and use sub(s) ... you can actually play any LP, CRANK the volume, and you have ZERO woofer pump?
Yes.
To be fair, I don’t use subwoofers - I use a full-range speaker system that is essentially flat in-room to below 20hZ.
last_lemming OP
639 posts
 
Larry,

I know it’s the TT per se, but it seems like some sort of interference is ramping up the pumping, because it doesn’t pump in the other room in the same set up - TT, cart, rack.

to you comments:

1. I have bought the ring. Hasn’t arrived yet
2. I have bear claws on a maple shade wood block, with the original prime feet secured to the wood block.  I have removed all these feet and tried various racks and also a concrete floor and carpet. Pumping is exactly the same in this particular room. Even on quiet passages. 
3. The TT is FURTHEST away from the right speaker where the pumping is worse. BTW the right speaker pumps more on all three TTs with 5 different carts and 3 different alignment methods. The pumping is exactly the same in all the different configurations. 4.  I did download a vibration program, but it must not be sensitive enough since the line is perfectly flat even on the most sensitive setting. 
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