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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?  


o_holter
o_holter OP
541 posts
 
Thanks tkr - but I live in Oslo.Thinking about the problem, I thought: maybe it is related to the Telefunken NOS tubes I use in the super sensitive first gain stage of the Aesthetix Io. So I pulled it halfway out of the shelf, enough to get off the top, and swapped the two Telefunkens in the right channel for a new pair of PSVANE 12ax7. Result? No difference. The pumping is still more visible in the right than the left channel. Then I swapped the left and right phono cables leading to the Io. Again: no difference. Right channel pumps more.

o_holter OP
541 posts
 
I disconnected the Aesthetix Io, and connected the ASR mini basis mk2. Playing Pink Floyd Echoes once more. Result? Very similar behavior. Subsonic pumping, strongest in the right channel. Even if the ASR has far less deep grunt in the bass compared to the Aesthetix. I was surprised! Clearly, like Atmasphere said, the phono stage is off the hook. 
o_holter OP
541 posts
 
I am back to square one. Invictus005 was right: "There’s nothing you can do. It's normal. .. Just live with it and when the stylus wears out get something else." 
o_holter OP
541 posts
 
Channel imbalance in woofer pumping? No. Mystery resolved. It turns out that one of the driver tubes in the left channel amp was going bad - at first, just weaker sound (and less pumping), but after plugging in the ASR and going back and forth to the Io, the sound became clearly distorted. Failure of a brown-base 67SN7GT Made in China. Replaced with a Electric Harmonix tube. Now the channels are equal in volume, and in pumping.
atmasphere's avatar
atmasphere
7,068 posts
 
@o_holter This really sounds like a turntable problem to me! I've dealt with this a lot; I repaired consumer electronics for a living right out of high school, through college and beyond. If its once per rotation, its something to do with the platter and literally can't be anything else.
To prove this out, change the speed to 45 rpm and you should see the pumping speed increase with it.
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