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

… 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.

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.)

Constant DC of one polarity will eventually damage the voice coil.

Only if the DC wattage is enough to cause the VC to rise beyond its temperature capability. A small amount will only slightly warm the VC… R*I = power and those electrical watts are the same as thermal watts.

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.

Yeah we talked about blocking caps back on page 2 or 3.

And now whether the frequency is low enough to use a blocking cap to also block close to DC would likely work, as the excursion is not really heard. But maybe some doppler distortion can happen? 

Since we do not know the causal mechanism, we are sort of jumping the gun for a solution, as we do not understand how to ameliorate the causal mechanism without knowing the causal mechanism. 

I do not think we need to know the amp, as the system does it only with XLRs and the RCAs do not exhibit it.

So it is most interesting thread in ages.

Like I wrote above, my research tells me the OP's preamplifier avoids use of a coupling capacitor by virtue of having a servo mechanism to balance out DC offset at its outputs.  Right there, that ought to prevent DC from getting to the woofer.  But if one wants to insist on a DC origin, then you have to postulate that the DC is somehow getting by the servo mechanism and also that it is pulsatile in nature, either pulsing between positive and zero or between positive and negative with a 180 degree phase difference, in order to make the woofer move as we see it moving. I mentioned that such servo devices are usually very effective in blocking DC.  My Atma-sphere MP1 uses such a circuit to avoid the need for a coupling capacitor, and I have measured DC offset at no greater than 2mV.  That is not enough to move a woofer, even if all of it did get straight through the ampifier to the speaker.  Some SS amplifiers do pass DC, but they don't amplify DC.  So, I am dubious that DC generated somehow from the cartridge is causing the problem.  But it did occur to me today that maybe the servo in the OP's preamp is defective when operating in balanced mode.  All bets are off.

@lewm It is not DC… by definition is like a sine wave or really more like a wavelet that is at a period of 33.3/60 of a second.
However it is maybe not a 1/2 Hz sinewave, more likely it is a flat line, with a heart beat that is happening over a just a fraction of the 360 circle.
So maybe it is a 5 or10 Hz thing that happens “at a rate or period” that is 33x/minute.

If it was DC the cone would be pushed out, but the cone was “pumping” and that is a verb or action word that describes something that is not steady-state… and not what a blocking cap or servo is designed to control… assuming that they are used for steady-state control.

…. So, I am dubious that DC generated somehow from the cartridge is causing the problem. But it did occur to me today that maybe the servo in the OP’s preamp is defective when operating in balanced mode. All bets are off.

The thing is perfectly synced to the platter, and the signal has to be coming from the cart, or has to be coming from the ground.

There is no other way the phone stage etc can make the speaker pump perfectly in sync with the platter.

Maybe it could be an intermittent DC shift on the ground, but the “no vinyl” “No mat” discounts that. And a servo will not remove it.

it is a conundrum.