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?
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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.
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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.
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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.
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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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Two lollipops then.
"No insult was intended." MY point.
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"I find a subset of people in the Analog section of the board who are terse, unhelpful and impolite if not outright rude and insulting. What could be more unhelpful than to present, as a fact, something that simply false."
Would you like a lollipop to make you feel better? I made an error in my preconception of the definition of the term "rise time", and I subsequently admitted as much. No insult was intended. Yes, things can get heated here once in a while. You came here with your mystery. Now you want to insist that you alone have solved it. OK. I read that your preamplifier uses no output coupling capcitor; instead, it uses a servo to balance out any DC offset in its output. So your preamplifier could in theory emit DC, IF and only if its servo corrector is not operating rapidly enough to prevent any DC offset in its output. But even then, the error in cancelling DC would likely be in the low mV range, perhaps not enough to move your woofer so obviously. (I say this because I use an Atma=sphere MP1 preamplifier that also uses a servo to cancel DC, and I have measured the error at 2mV, max.) I don’t know what amplifier you are using. If your amplifier uses a coupling capacitor at any point in its circuitry, then the amplifier cannot pass DC to your speaker, even the low level that might theoretically get past your preamplifier. Those are just facts. Not insults. I am only interested in getting the facts straight, because if you write something here that is just not possible based on facts, then some other reader may be misled. I operate on the assumption we are all here to learn.
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Sorry. I’m wrong when I wrote DC has no rise time. I still doubt DC is moving your woofer at whatever low frequency it’s moving. And constant DC of one polarity will burn out a voice coil. If it’s rapidly changing polarity by 180 degrees perhaps not.
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Show me or describe the wave form. You could be describing a square wave, which is complex AC. DC seen on a scope is a flat line with respect to time. The vertical position of that line will depend upon magnitude. DC into your woofer might burn up the voice coil but won’t move the diaphragm. Whatever the source is that’s moving your woofer it is an AC signal doing the work..
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DC has no "rise time", by definition.
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The idea that the ES charge is concentrated at one area on an LP or on the mat is contrary to data collected by Shure Corporation, when they studied ES charge in vinyl reproduction, albeit many years ago; they suggested that charge distributes evenly across an LP surface. However, I could perceive that there might be some assymmetry to charge distribution due to fingerprints or other oily or watery deposits on the LP surface. So perhaps the data you cite would contradict their earlier findings. I will take a look.
And we still have not had an answer as to whether the 18Hz high pass filter on the preamp was engaged during all of these investigations. If it was engaged, then I would expect there to be little to no woofer pumping when the platter is spun at speeds below 18Hz. Yet I thought the OP reported he can spin the platter by hand at speeds well below 33 rpm, and still visualize the phenomenon.
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How do you explain the periodicity? Wouldn’t the mat be uniformly charged?
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Pixies for sure.
since no hypothesis offered so far really holds water, who is to say that a step up transformer would not eliminate the problem? But do you wish to continue to operate in balanced mode? I thought you got rid of the problem simply by converting to single ended mode. If you are happy with single ended mode, why think about a step up transformer.?
Is it really the case that you’ve been using a hi-pass filter operating above 18Hz in all cases? You earlier stated that if you move the platter manually at sub 33 rpm, presumably at and below 18 rpm speeds, the pumping occurs with frequency proportional to platter manipulation. That seems impossible so I must misunderstand.
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"If the signal was sneaking in on the ground, then the SE is tying the phono stage to the TT. And the pin-1 being disconnected, is not tying the XLR to ground.
But this also would suggest that the XLR at the TT side may not be wired as push/pull and maybe has the out of phase side tied to ground?"
You lost me there, but I am not suggesting or even thinking that the signal is coming in on the ground connection. Quite the contrary, the balanced connection is floated (not attached to audio ground), and the phenomenon only occurred in balanced mode.
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In connecting a cartridge in balanced mode, to a balanced phono stage, ground is left to "float". As you know, the cartridge has no ground connection, per se, except for a very few older designs, like (I think) old Decca cartridges, and those cannot be hooked up for balanced drive. The shield on the phono cable itself, if there is one, can be attached to phono stage ground lug, but I have three TTs operating in fully balanced mode, and in no case has it been necessary to ground anything to anything. I don't see any problem with Mitchell's wiring scheme, certainly not one that can account for the phenomenon. And it's not confusing.
Someone else very early on mentioned the Hall Sensor, which is very likely used in the drive system of the Yamaha, because it has a DC coreless motor. On my Kenwood L07D, also coreless and also DC, the Hall Sensor is fixed to the plinth surface under the platter, but there must also be a signalling device built on the underside of the platter itself that rotates with the platter and triggers the sensor if there is a speed error. It seems possible that in balanced mode the phono stage is picking up a signal from the cartridge, as the Hall component that is fastened to the platter rotates under the cartridge. This is causing an impulse from the cartridge to push the woofer in concert with TT speed. But why this happens only with platter mat and LP in place, I do not know.
One idea why the problem only occurs in balanced and not in SE mode might be that in the latter case, both channels ARE connected to audio ground, so maybe the signal never gets to be amplified to drive the woofers. It would be interesting to hook the output to a 'scope and see if one can detect the spurious signal on hot or ground in SE mode.
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My oscillation hypothesis is officially in the toilet, if the frequency of the woofer pumping is equal to the TT rpms. Over and out.
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In the post above, the word "isolation" which appears in line 9 of the second paragraph, should be changed to "oscillation". I thought I fixed that within the time limit for editing, but apparently not.
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Not everyone is focused on magnetism. Have you read any of my posts? I’ve just grown weary of contradicting Holmz, who IS focused on magnetism. I let his last fantasy stand as is, because I did not want to appear to be picking on him.
Like I have said three or four times, my best guess is that the system is oscillating at a very low frequency when the preamplifier is hooked to the cartridge output in balanced mode. When the OP switched to single ended mode, the problem went away. The bit about the platter mat and LP is a red herring, as per my earlier definition. The fact that it seemed to make a difference can possibly be due to the fact that when you power down an oscillating electronic device (in this case, the preamplifier or the amplifier would be oscillating due to input from the TT), the oscillation of course ceases. When you then restart or power up the same electronic device, even with the same input and output loading, the isolation may or may not reappear. In order to remove the platter mat and LP, in this instance, the OP had to shut down power to the TT and then power it up again in order to demonstrate the "no platter mat, no LP" condition. So lets say the cartridge is picking up something from the TT motor that intermittently causes either the preamp or the amplifier to oscillate but only in balanced mode. The intermittent nature of an oscillation is what confounds the investigation of its cause, let alone trying to fix the problem. And beyond that, we really do not have enough data to speculate further. Maybe the OP will eventually come forward with some additional information, but I don’t blame him if he does not want to be bothered and is perfectly happy to operate in SE mode.
Magnetism, shmagnetism.
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fsonic, Mea culpa. A thousand apologies. It was Holmz who wrote the sentence I quoted (and responded to), not you.
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fsonic, I don’t know what I said to make you so angry, but you DID write, ..."or degauss the current mat, or put a blocking capacitor somewhere." And this is what led me to believe that you were supposing that a capacitor can block a magnetic field. Even Sherlock Holmes could testify to that fact.
Mitchell, I apologize if you felt that I was discounting the thoroughness of your analysis. I was not, although your report as it is does suggest a few other experiments that could be done to investigate the matter further, rather than for the rest of us to just keep on guessing. The first of those would be to re-install the XLR connectors and determine whether you can reproduce the original phenomenon. But I also understand what a pain it is to change the connectors on your ICs, and if you don’t want to be bothered, that’s fine.
My point was and STILL is that it could be that some piece of gear in your signal chain (originally I mentioned the preamplifier, but it could also be the amplifier) is induced to oscillate under certain conditions. And this may have nothing whatever to do with the platter mat plus or minus an LP on top of it. (Hence, I used the term "red herring" in reference to the bit about the effect of the platter mat/LP) Oscillation can be very capricious, intermittent, and nearly impossible to reproduce when you want to investigate its cause. Turning a unit off will stop its oscillation, and when you apply power again, the unit may work fine under the exact same input and output loads. Like I mentioned, I have had a personal experience with an unstable amplifier that vexed very competent repair persons and then vexed me for another year when I took on the job of fixing it because no one else wanted to touch it. This amplifier oscillated when fed by a certain CDP but not when fed by another CDP, for example. On other occasions, the amplifier worked fine for months before it would go into oscillation solely due to music input. From a pragmatic point of view, if you are happy with SE operation, and if your particular problem never recurs, you really never have to know what was going on. Just enjoy the music.
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A capacitor does not “block” a magnetic field.
but that’s not so much of a problem, because there cannot be a magnetic field generated from the Funk Firm Acromat, because it is completely non-metallic, let alone non-ferrous. (See the FF website.) I know there are some who believe that records can become magnetic and need to be degaussed periodically. I am not one of them, but even if it were so then we would all be having this kind of problem, and we don’t. Furthermore, a magnetic LP would attract the magnets in a cartridge, and could be disastrous for the suspension, but that doesn’t happen either. Furthermore, if LPs could be magnetized, they would become uniformly magnetic; the magnetism would not be patchy across the LP circumference so as to cause the phenomenon the OP observed.
As I said above and still believe, I think the story that goes with the observation (removing the platter mat and LP cured the problem, etc) is a red herring. If the phenomenon was to be further investigated, in other words, all that bit would be seen to have had nothing to do with the actual cause. For example, it is possible that the phono stage has the potential to oscillate at a low frequency when in balanced mode. Such an oscillation can easily be a some time thing; in other words it comes and goes. In the story, the OP had to shut down the turntable to remove the platter mat and LP. This might stop the oscillation that is really going on in the preamp, just by chance alone. When he switched to SE operation, that too would require shutting down the phono stage, and it could easily be the case that the premp does not oscillate at all in SE mode. If you have ever tried to chase down and cure an oscillation in a piece of audio gear, as I have done, you would know what a royal pain in the arse it can be. Took me over a year with an amplifier, and that was with help.
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Good find, Dekay. For a true balanced hook-up from cartridge to a true balanced phono stage, audio ground is typically floated (no ground, in other words). Pin2 of the XLR connector is typically connected to the positive phase ("hot" on an RCA connection), and pin3 carries the negative phase (the outer barrel of an RCA). Pin1 can be connected to shield but not to the cartridge. Maybe there is a wiring problem that only pertains when operating in balanced mode. But I hate to say this, the video shows the problem goes away when LP and platter mat are removed, even though he is still (I think) operating the system in balanced mode at that point. If we can throw out that bit of information, it makes more sense. (Just kidding; we are stuck with the facts of the matter.)
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He’d have to reinstall the XLRs and switch to balanced mode on his preamp in order to revisit the problem, and he prefers not to do that. So further conjecture is futile.
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The platter is solid aluminum. Even if it had a layer of another metal hidden below, it would be a solid circumferential piece. It makes no sense to invent possibilities that are very remote and then feel satisfied that you know what is going on. And even more important, if you watch the video, the pumping ceases when the LP and platter mat are removed!!! If the platter per se was the cause, that would not happen.
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Could be something is oscillating in balanced mode but why would it go away when you removed LP and mat? Neither of which can “store energy” for more than milliseconds. And it would be kinetic energy, not electrical.
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I think it’s a red herring, meaning something else is or was going on that neither we nor the OP have detected. Which is why I asked the OP to see if he can recreate the phenomenon by restoring the original conditions. It cannot be the platter per se because we see the pumping disappears when LP and mat are removed. Funk Firm mat contains no metal either. I’d bet the pumping has either directly to do with balanced mode or has nothing to do with what we see.
I certainly don’t blame the OP for not wanting to change back to XLRs just for my/our benefit.
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The OP clearly stated and also shows in the video that he’s using a Yamaha GT2000L, a very fine vintagE DD TT with a coreless motor. So far as I can determine that platter is all aluminum. Which is why I asked about the platter mat, wondering whether it might be ferrous. I know nothing about the Funk Firm, but I’m guessing it contains no iron or copper.
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Sorry but you have to prove that balanced input makes a difference by reverting to XLRs and re- testing. Also, is the phono stage actually balanced or does it just offer XLR inputs? Also retest with vs without platter mat. Also, what platter mat?
Has nothing to do with DC on the AC line by the way. DC is DC; has no frequency.
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If TT is turned off, does problem go away.? If so then I propose that the spinning platter has some iron content and this is inducing a very low frequency signal in the cartridge which is then amplified and affects the woofers.
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