Needledroppers - help invent a polarity test by (literally) dropping your needles

Thanks. Learn something new every day.

 

Thanks for the information missan. So it’s becoming clear to me that the stylus is climbing the left wall on positive peaks of velocity and losing contact with the right wall at or near peak velocity. This explains why the distortion occurs at opposite polarities in the left and right channels.

When I think about it, as the direction of the groove changes at the peak excursion the signal must pass through zero.

 

Yes for a pivoted arm with an offset angle, the needle is very likely to climb the inner left wall when tracking difficult passages.

 

Tin ears, I don't know if you're still following this thread but earlier you said you got opposite polarities from an AT440Mla and a Shure M97xE. I've just tested my Shure 97xE and it tests the same polarity as all the other cartridges I've tested on the same setup, including my AT440MLa. (The other cartridges I've tested are the AT33PTG/II, the AT150MLX and the Shure V15VxMR.) In post #125, moogt3 also indicates that he's tested the Shure M97xE and the AT440MLa and as far as I know, he's getting the same polarity from both. So I wonder if the inversion you saw crept in some other way?

Meanwhile I've been refining my testing technique. It's definitely better to take off the antiskate if it can be done without too much trouble - any sideways movement can give unclear or unreliable results. And I've found I get the best results by not using the cueing lever. Instead, I push it all the way down so that the cartridge is free to drop. Then I use the fingerlift to drop and raise the cartridge repeatedly. I get lovely, big, clear spikes that way.

I'm also sending out some emails to try to get confirmation of what we've found out about polarity.

 

One year later...

Today I travelled all the way to Bristol for a hi-fi show where I had good reason to believe Mr A. J. van den Hul, the man behind the cartridges of the same name, would be present. I found him, cornered him and threatened not to let him go until he told me which channel was inverted in a standard audio cartridge.

It was a faintly bizarre and very frustrating conversation. He told me that when he makes a cartridge, he uses an old CBS test record and an oscilloscope to make sure he has the polarity of the magnets the right way round. But here's the thing - he flatly denied that one channel was inverted relative to the other. When I said it had to be because the groove in the LP was cut with one channel inverted, he flatly denied that, too - he said there was no inversion anywhere, either in the groove or the cartridge. When I said there had to be because otherwise the left and right channels would cancel each other out when playing back a mono record, he said he was only interested in stereo.

I could hardly tell him he was wrong - he's been making cartridges for 40 years and I can barely make toast. But he is. He doesn't realise that the test LP he uses is cut with one channel inverted, and the magnets he's fitting probably aren't marked for polarity either, so when he drops the needle in the groove and sees a double positive, he thinks both magnets are firing in the same direction. We know that's impossible because if it was true, you wouldn't be able to play a mono record with a stereo cartridge, but I can only think he's never stopped to think that through.

Oh well, the search goes on. I know we're 99 per cent sure it's the right channel that's inverted but I won't be happy till it's 100 per cent certain. I did ask Mr van den Hul what test record he used but he couldn't remember the number. He said it wasn't a CBS consumer test record like the STR 100 but one that was made for audio professionals. I've Googled it but I can't find any CBS test record that has a polarity test so I don't know what he means.

Sorry not to have better news. Next update in February 2016...

 

99.9%, but the waiting is the hardest part.

 

Nagaoka MP-500:

 

Nice forum although this topic is in slow motion right now.

I found this forum while trying to solve a polarity/bias problem. Both my Pioneer and Empire cartridges are wired correctly but produce an inverted wave form of each other when recording. No amount of anti-skating altered the bias. The Pioneer sounds better and I noticed that most clicks/pops occur on the positive side for the left channel, just the opposite on the Empire. I think this matters because it gets the most oomph out of the recording. As an experiment, just blow on your finger at 2 inches then suck the same amount of air pulling in. You can't feel the negative pressure. Pushing air (sound waves) is more efficient then the pulling.

I tried the paper pull test and sure enough the Pioneer was biased positively when pulling the paper towards the record rim which in effect is pulling the stylus toward the rim. If the previous post is correct then the Pioneer cartridge has the correct polarity. I have a screenshot which shows the Pioneer cartridge vs. the Empire but haven't figured out how to post it.

 

I’m re-opening this thread to pass on some news – finally, we have a definitive polarity test for vinyl playback!

After last posting on this thread back in February, I quietly spent months trying to get official confirmation of what we’d long suspected: that pushing the needle outward, towards the record rim, should produce a positive signal in both channels. It was amazingly difficult to get this confirmed.

I eventually wound up with the IEC, which is the European standards body. They had an old standard on analogue playback called IEC98, now re-numbered 60098. It’s far too expensive to purchase a copy of the standard and it’s not to be found anywhere online. But after a few email exchanges the IEC very kindly agreed to help answer my question. In fact, they ended up passing me on to the equally helpful British Standards Institute who told me that they had an identical British standard, called BS 7063, covering the same territory, and they sent me the relevant extract.

And ta-da! Here’s what it says:

11.4.4 Channel polarity

Stereophonic reproducing equipment should preferably be so connected that movement of the reproducing stylus tip along the radial line through stylus tip and disk centre in a direction away from the disk centre shall produce compression in front of the left and right-hand loudspeakers similar to that produced by the live programme source.​

“Compression” means a signal that causes the speaker cone to move towards the listener, which in turn means a positive signal. So we finally have our confirmation, that a horizontal movement of the stylus towards the rim produces a positive signal in both channels.

Elsewhere, the standard also states that the outer groove wall represents the right channel. Well, we knew that. But the point is that, with this piece of information, you can easily deduce which channel is inverted, as follows:

Any hump in any groove wall produces a compression of the needle, and compression = positive. Any valley in any groove wall produces a rarefaction (or decompression) of the needle, and rarefaction = negative. When the needle is thrown towards the rim of the record, that’s because it’s experiencing a hump in the inner groove wall which is the left channel and a valley in the outer groove wall which is the right channel. So that means you SHOULD be getting a positive signal from the inner groove wall (left channel) and a negative signal from the outer groove wall (right channel). But In fact, you get a positive signal from BOTH channels. Therefore, the right channel is inverted.

I’ve made this diagram, based on an existing image I found on the internet, to make things clearer. The red pole piece (probably not the right word but you get the idea) is picking up the right channel and the white one is picking up the left channel:




Using this information, it’s easy to devise a polarity test for vinyl. You’ll probably come up with your own test but one way would be to do the drop test that I originally proposed right at the beginning of this thread. With that test, you do need your vinyl rig to be hooked up to some kind of waveform editor on a PC, but once having achieved that, all you do is drop the needle vertically onto the deadwax with the turntable stationary and look at the spikes in your waveform. You should get an upward (positive) spike in the left channel and a downward (negative) spike in the right channel (because the right channel is inverted). If you don’t, then either you’re using an unorthodox cartridge that doesn’t follow the standard, or something in your vinyl playback system is inverting absolute polarity.

Some more thoughts:

1. Just a reminder that, although the cartridge inverts the right channel, it’s not playing your records back wrong. When your records were made, the cutter head inverted the right channel, so the cartridge is simply putting the signal back to how it should be. All this was set up when stereo records were invented so that mono records could be played with a stereo cartridge. If things had not been arranged this way, you can see from the diagram above that mono records would not have played properly with a stereo cartridge because the signals coming through the left and right channels would have been matching but opposite and therefore would have cancelled each other out.

2. It’s interesting that the standard lays down a preference rather than a cast-iron rule. That would seem to confirm that correct absolute polarity was seen by the industry as desirable rather than essential. In reality, I’ve seen (and continue to see) large numbers of records, CDs and even digital downloads where the absolute polarity is obviously wrong and I long since gave up worrying about it.

3. As I’ve said, the IEC and BSI standards on this are the same. From a Japanese website, I’ve learned that the Japanese standard also states the same. I haven’t seen a US standard but it seems inconceivable that the US would be doing the opposite and indeed I seem to remember that Stan Ricker said outward = positive so that seems to confirm that there’s a single global standard. (It would be madness if there weren’t.) So far as we’ve been able to establish in this thread, all the big cartridge makers, including Shure of the US and Audio-Technica of Japan, follow this convention.​

I’m going to open a new thread in the next day or so telling anyone who’s interested how to carry out this test so they don’t have to wade all the way through this thread to find out. Congratulations to all those who contributed to this thread and helped invent the world’s first DIY polarity test for vinyl playback!

 

Nice job, good to have a confirmation of what we 'knew' was the correct behavier.