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So Weird- No Stylus Contact Woofer Pumping with Hana ML and Elac PPA-2

I observed the weirdest thing I have ever seen in audio. With the cartridge positioned above the record, tone arm locked up and platter spinning, the woofers were pumping on my system. I googled every permutation of query I could think of but came back with no hits. That’s when I decided to video the problem- link below:

Mystery Woofer Pumping

I could type out all the details but the video pretty much covers everything. I thought ya’ll might be interested in this.

 

mitchellcp
mitchellcp OP
86 posts
 

Would you like a lollipop to make you feel better?
 

My point

lewm
13,293 posts
 

Two lollipops then.

"No insult was intended."  MY point.

mitchellcp OP
86 posts
 

The problem isn't solved really. That woofer pumping should not occur to that extent. I believe there is a problem with the ELAC PPA-2 balanced input. Both single end inputs function fine. I'll be looking into it this weekend. I bought to unit on US Audiomart so no warranty for me.

holmz's avatar
holmz
2,328 posts
 

… DC into your woofer might burn up the voice coil but won’t move the diaphragm…

@lewm

That is false… DC will make a constant magnetic field that will then push the diaphragm off center.

It would need to be a pretty high offset to deliver enough energy to move it to overload the woofer thermally.

If it is not moving the diaphragm, then there is no AC and no DC.

 

Whatever the source is that’s moving your woofer it is an AC signal doing the work..

Yes AC, but AC that is at a low frequency.
Hence my earlier suggestion of a DC blocking capacitor, which blocks low frequencies.

But the freqs needing to be quashed, maybe higher than 20Hz as the table is turning at ~2Hz and the think is rising and settling over a small angular extent.

The problem isn’t solved really. That woofer pumping should not occur to that extent. I believe there is a problem with the ELAC PPA-2 balanced input. Both single end inputs function fine. I’ll be looking into it this weekend. I bought to unit on US Audiomart so no warranty for me.

Even more troubling @mitchellcp is that the causal mechanism is not known.
It would be interesting to try another phono stage that is balanced to help identify you hypothesis of the ELAC. But it seems like a rational conclusion.

A pragmatic person might just chuck in the RCAs.

lewm
13,293 posts
 

Ughh.. Holmz, DC will move the diaphragm in one direction only, yes. Constant DC of one polarity will eventually damage the voice coil. I suppose intermittent DC pulses could appear as if a low frequency AC source, but….The question is whether the preamplifier and amplifier can pass DC from the TT to the speakers. And DC of sufficient magnitude to move the woofers. His preamplifier uses a servo mechanism to cancel any DC offset at its output. (See review by Fremer.) I don’t know what amplifier is in use but many block DC. Any coupling capacitor in the amp circuit would suffice to do that. (Amp may have been mentioned but I’ve forgotten.)

 

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