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.
|
Holmz, I have been saying forever and I’m sure ad nauseam that I don’t think it’s DC. So if you’re addressing me, you’re preaching to the converted. We agree.
|
Nothing that has been offered as solutions seem viable. Static is random, forget about it. The only suggestion that makes some sense is the the possibility on a weight sensor on the table to detect record weight. The Achromat is much lighter than the rubber stock mat on my old SP-15.
|
Nothing that has been offered as solutions seem viable. Static is random, forget about it. The only suggestion that makes some sense is the the possibility on a weight sensor on the table to detect record weight. The Achromat is much lighter than the rubber stock mat on my old SP-15.
Agree @waltroman - but ignoring a solution, how does the static manifest itself into the signal wires?
I would think that both the + and - wires would be elevated equally and in the balanced sense they should then cancel out with the CMRR of a balanced approach.
|
Weekend results- using a signal generator I input square waves into the phono pre at all three possible inputs, input 1 RCA, input 2 RCA, and input 2 balanced XLR. All three output clean square waves at normal operating frequencies at various amplitudes. I couldn’t trip it up. So I’m eliminating the preamp as a culprit.
|
I reinstalled the XLR and using the Hi-Fi news test record 300 hz bias test track 6, just for the 300 hz signal, I again got the woofer pumping. The signal rides the rising and falling baseline. With the cartridge lifted but over the record the signal is flat, rising and falling.
|
Also I input square waves at the phono cable end and scoped the cartridge end with the cartridge connected- all square with the left and right showing a slight amplitude difference. My next plan is to try to bypass the arm and phono cable wiring with an alternate set up mounted external to the arm to see if the problem repeats.
|
|
SOLVED- Short answer, my fault. The Audio Note silver litz is notoriously difficult to work with and in this case my reach exceeded my grasp. The o-scope trace of the left vs the right channel was different by about 15%. I figured there had to be something there to explore. I desoldered the wires to take a look under the microscope and saw very few clean areas free of urethane. Every connection point was wildly different.
I picked up an el cheapo solder pot so I would theoretically have an advantage clearing the goop. The trouble with el cheapo Amazon solder pot is that the temp controller swings too wide. Just when a wire was almost there- zap- melted in the pot. I need 13” of wire and at some point my second wire ended up at 12”. No more Audio Note wires.
I reinstalled the original Mogami set. This was designed for MC cartridges and despite my concern for the mass that the original setup adds, with the Hana ML it worked out to a tone arm resonance of 10 hz. The original set is copper and unlike the Audio Note it’s obviously larger than a human hair. It has the added advantage of existing within my skill and equipment set.
At any rate, the effect of static on the cartridge is gone. To be honest the circa 1970/80’s wiring sounds very good. I had originally pulled the factory set because it’s curiously heavy and the mass was too much for a 2M Black, I also suspected an electrical mismatch in design.
The PPA-2 using balanced input and balanced output is a different animal than in single end mode. It wipes the floor with its unbalanced self. More transient energy by a mile. It really comes alive.
This thread is solved, if nothing else, if someone else tumbles into this scenario it may help.
|
I'm stumped. What do you reckon was the mechanism of your original observation? Which is to say how do you suppose the wiring fault had something to do with the woofer movement? I am not at all challenging you or trying to contradict you; I am just truly curious, even though I do not doubt that you may have had some bare wires somewhere in your arm tube, if that is what you are suggesting.
By the way, I too tried to work with the Audio Note silver Litz, and I too used a solder pot. I melted more wire than I soldered, and in the confusion, the four wires got hopelessly entangled with each other. It's a job for a pro who preferably works with that wire every day.
|
I understand that resistance is additive in series. So in one sense there is no possibility where there would be an EM potential difference. However I saw on the o-scope various differences between the left and right channels that increased in amplitude as I lowered the input frequency. I figured all this was reactive- an impedance change. Also it was disappearing in single end- linking the ground fixing the problem, at least as I understand it. I was in the Submarine service and got a nice commendation for recommissioning a failing hovering system, it was a corroded solder joint. That’s how I got to a garbage solder joint as the possible cause. Change wire, add solid connections- problem gone. I figure someone in 2056 will have this trouble and thank me after I’m dead.
|
Also- you were right about the AC- it was going positive and negative, slowly but plus and minus none the less. Apologies.
|
Apologies not necessary. Suffice to say you found a glitch in the wiring and fixing the glitch also cured the woofer pumping. Is that a fair summation?
|
I’d say that’s the highlight
|
