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
dcmnto
7 posts
 
No idea if this will help or if you have eliminated these potential causes, but I had a similar issue with my Pioneer and in my case there were multiple things happening. 

The one cause was the turntable being too close to the magnetic fields of my open baffle subs.  Moving the turntable helped.

The other cause (which is less likely in your case) was that the potentiometer (dial) used to adjust the speed had dirty contact issues which caused the direct drive to "flutter" for the lack of a better word. You could see the speed changes on the strobe. The magnetic fluctuations as it kept trying to adjust the speed were picked up by my MC cartridge making the bass pump. A dose of de-oxit sorted that out.

In either case and EMF meter could help determine if a magnetic field throughout your home is the source.





tom2015
96 posts
 
As has been said before the KAB rumble filter will fix it without any sound quality loss. I added between 2nd pre out and subs so no effect on highs/mids and the pumping stopped. Bass is actually better and more defined compared to before. 
mulveling's avatar
mulveling
1,908 posts
 
Despite swapping out turntable/cart/phono stage, your constant factors here are: your rack/mounting/floor under the turntable, its location (relative to the speakers too), and your (lack of) clamping over the whole record surface. You could leave everything as-is and attack this with the KAB rumble filter, but other than that these are the variables to play with.
last_lemming OP
638 posts
 
Yes the KAB is an option, but I want it to be my very last, but only after every other variable has been looked at. While I know some say it’s transparent, others have said otherwise.
To be clear the rack has not been constant. Anything but. The TT’s have been on concrete, carpet , rack, on and off maple block, with and without bear claws, different locations in the room, with and without record clamps, and all this tried with three different turntables, two amps, two preamps, three phono amps, different speaker cables, various IC’s, and even different power cables and outlets.  

It’s something with the room. I can’t figure what, but I’ve basically changed all components out, so what’s left is the room, and it’s not room interactions, because I hooked up a speaker with a very long speaker cable and ran the speaker outside the room the equipmentIs in, and it still pumped.  
It’s driving me nuts!  I don’t want to add a KAB to fix a problem that is not caused by the equipment.   



mtemur
11 posts
 
cause of the pumping woofer is rumble and it's inherited to vinyl playback. there is inevitable friction between tip of the stylus and groove walls while playing. additionally if your stylus is worn out it can reach the bottom of the groove and cause more rumble.

on the other hand turntable, tonearm and cartridge quality plays a major role on rumble but unfortunately you can not totally eliminate it. you can only lower it to an acceptable level. people who are saying that there is absolutely no rumble on their turntable are either not aware of the existence of an embedded rumble filter on their phono preamp which can not be turned off or don't have a speaker that can go below 40Hz.

in order to lower rumble to an acceptable level you need a much better turntable and tonearm than the ones you mentioned.
More to discover