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.
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?
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- 185 posts total
@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. |
@o_holter I must echo armasphere. Pumping once per revolution is not electronics. It has to be bearing or platter related. It acts like a warped record. Have you checked to make sure your platter is dead level? Put a small bubble level on the platter and turn it slowly by hand to see if it is level through a complete rotation. Repeat this with the level in different places on the platter. Don't use one of the small round levels supposedly designed for turntables. Use a fairly short (6 to 8 inch) carpenters level. Second, have you checked to make sure the platter is not wobbling on the shaft? Good luck. |
analogluvr"Are you able to turn down the gain on the phonostage?" It has become increasingly obvious and apparent that the underlying responsible problem this particular user is experiencing is related to his turntable and possibly although not likely his cartridge/tonearm combination and there is no way that the gain of the phono stage could have any effect influence or ability to correct the problem which the user doesn't seem willing to take the steps necessary to resolve anyway. |
- 185 posts total