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

I've discovered my SACD player inverts polarity (reverses positive and negative, so the waveform comes out upside down) and I'd like to prove that my vinyl setup doesn't do the same. I've been struggling to think of a way of doing this but then I thought, well, if I just drop the stylus on the record, it should produce an upward (positive) spike in the waveform, right? To my horror, it produced an upward (positive) spike in the left channel and a downward (negative) spike in the right! But I think this is because the coils in a stereo cartridge are arranged in such a way that an upward vertical movement of the stylus produces a positive signal in one channel and a negative signal in the other. The trouble is, I don't know which is which.

With your help, we could easily produce a polarity test for vinyl setups. All we need is a majority verdict on which way around the signals should be.

If you'd like to help, all you need to do is:

1. Open a new file in your waveform editor and hit the "record" button.

2. Literally drop your stylus (gently!) on a flat area of vinyl - maybe a few times to make sure you get a consistent result.

3. Look at the spikes in your waveform editor - both channels.

4. Post here whether the spikes in each channel go in opposite directions. If they do, please say if it's up in the left and down in the right, or the other way around.

With any luck a pattern will emerge and before you know it, we'll have invented a simple polarity test!

 

Here's one I did a few hours ago, I'm in the middle of doing some Boston right now, do you want deadwax or music?

 

Sorry, c-eling, I didn't explain it properly. THE TURNTABLE MUST BE STATIONARY - that's the point I failed to make. All that's needed is a picture of that single little bump as the needle hits the vinyl, which should produce a nice big spike in the waveform editor. A flat section of vinyl would be best because we want the needle to hit the vinyl at 90 degrees.

I can't get to my turntable at the moment but I'll post a picture tomorrow to show you what I mean.

 

Gotcha, give me a bit, in the middle of Aja at the moment

 

With an Audio Technica MM cartridge:

 

Ortofon Concorde - Yep, Upward in the left and downward in the right. Has to be because of the movement of the cantilever inside the cart

 

Yes! Yes! This is so exciting! (I'm easily excited.)

We're making history here - crowdsourcing the world's first ever simple polarity test for vinyl rigs!

Here's mine:



That's five drops. You can see that each drop consists of a big spike where the needle hits the vinyl, then a wiggly line (slight reverberation, I suppose), then another spike where I suddenly lift the needle OFF the vinyl again. Then silence, then the next drop. (I exaggerated the y-axis to make things clearer.)

In each case the initial drop produces a sharp upward spike in the left channel, mirrored by a sharp downward spike in the right channel. That's the same as other people's results so far.

Still waiting to hear from c-eling though - he's been listening to Aja for 14 hours now.

Please, please, post your results too. You don't need to post a picture - just four words is all that's needed - either "Left up, right down" or " Left down, right up".

I reckon if we get a straight run of around 10 consistent results, we'll have ourselves a polarity test. If they start coming in mixed - well, we'll worry about that when the time comes.

 

Sample size is still low, back2vinyl, but I don't expect any further surprises for the result.

For anyone that might be apprehensive about "dropping the needle", I did my test shown above by just starting a record, lowering the needle onto the lead-in, which is sufficient to see that initial spike. Then, when the stylus catches the lead-in groove, you'll get a second spike in the left channel (you can just see the start of that in my screenshot), but that's not in question here. Anyway, just adding this as an alternative.

 

Yes it´s up in left, down in the right here too. You can also place the needle on the run out and gently tap the headshell.

 

Denon 110 MC Series of four-

 

Well done, missan and c-eling.

Tell you what, let's keep a tally.


Left up, right down
Antares
druboogie
back2vinyl
missan
c-eling

Left down, right up
None so far


We really could use some more results so please do post.

The reason for all of this is, if you look at an LP rip of a piece of music in waveform, and then look at a CD rip of the same piece of music, you'll often find that one of the waveforms is upside down relative to the other - in other words, positive and negative have somehow become reversed. I'm trying to find out why this is happening. If we can devise a test that rules out our vinyl rigs, that's a step towards finding out what's really going on. And it'd be a useful test in any event, just to check everything's as it should be.

 

Earlier this week, I captured samples of all of my gear playing the frequency sweep from my recently acquired CBS STR100 Test Record (NM for $3!), so I already the had waveforms handy.

cartridge / status

Stanton 681EEE / Left up, right down
Stanton 680HiFi / Left up, right down
ADC PSX-40 / Left up, right down
Audio-Technica AT247E / Left up, right down
Audio Technica AT-3830 / Left up, right down
Shure N70B / Left down, right up*

from a recent 78 drop
Shure M78s / Left up, right down

* - this is the only cartridge I am using with my recently restored Dual 1214.

 

Absolutely! (pun sort of intended)

Thanks for thinking of this. I checked the wiring on the Dual, and it shows to be correct. It can't be the phono stage or anything else downstream, as all of that's shared with the BSR linear tracker (which shows as correct) - so I went ahead and flipped the polarity of both channels at the headshell. Now it matches with the others.

Again - very cool of you for bringing this up. I've been thinking of using the Dual for ripping some of my more "distressed" 45s, as the Shure conical setup does a nice job of covering up the nastiness you can get from worn styrene.

 

I'm sorry, this doesn't seem like usable science to me - very random. Isn't there a test record with an absolute polarity test on it?

 

What effect will/should the results have on our needledrops? Should be inverting one channel post-drop?

 

Would the drop not tend to produce one result with vertical compliance and another with lateral?

 

Excellent! Thanks so much, Sid Hartha. Strange about the Shure N70B but it was always possible there might be one or two cartridges out there that invert - that's why we need plenty of results.

I've tried to make it a fair test in a scientific way. Why do say it's random? Dropping a stylus on a flat surface requires no skill or expertise and my tests have shown you ALWAYS get the same result no matter how many times you do it. It's extremely simple and totally reliable - surely that's the best kind of test there is? There's no readily available test record that provides an ABSOLUTE polarity test (as distinct from a channel orientation test). There's apparently one on Denon Audio Technical Test Record XG-7003 but I've never seen a copy of this record available. Best of all would be if some expert would simply tell us which way the coils are aligned in a stereo phonograph cartridge - they're obviously in opposite phase but we need it confirmed that a vertically upward thrust produces a positive signal in the left channel and a negative signal in the right - except in the Shure N70B!

No, don't worry, this isn't about one channel being out of phase with the other. It's about the polarity being reversed on BOTH channels. Imagine you walked over to your speakers, disconnected the speaker cables and re-attached them the wrong way around - red to black instead of red to red, etc. And imagine you did that to both speakers. Very probably you wouldn't hear any difference but you still might feel it wasn't quite right and prefer to have it the right way round.

 

Hmm, I'm not sure if this answers your question but are you aware that the coils both face downwards at 45 degrees off the perpendicular, in a sort of V configuration (but at right angles to each other)? It's not a case of one pointing downwards and the other pointing sideways. It's called the 45-45 system if you fancy Googling it.

 

Just to be sure I did a ****inuity check. So now after everything is connected as it should be, left is down. Don´t know if it means anything, the digital recording could very well reverse the phase. Anyhoo left is down, without a doubt.

 

Googling shows the Cardas test LP apparently has one, too. Dropping the needle is an unscientific test for what you claim to be testing because there are so many undefined variables. You're looking at computer generated "waveform" readings from different programs, rendered on different computers, through different phono preamp stages and unknown (random) analog and a-to-d circuitry. How do you know any stage in between isn't inverting absolute polarity? There's a 50/50 chance any given stage is as it's not considered important to most gear manufacturers (especially at the low end, but also extending as far up the line as your SACD player if you're right about that), and most of these readings are probably at the end of three or four random stages.

Using the same source throughout and defining the measuring point is what would move towards making this a scientifically useful test. Ideally the measuring point would be right at the cartridge or turntable leads, making the only variable the cartridge and arm cabling manufacturer's markings, but that would require a real oscilloscope with pretty high gain which is probably inconvenient for crowdsourcing like this. And as you say a suitable test record is not widely available. I would suggest a record that probably is widely available among your intended audience - Pink Floyd's Dark Side Of The Moon, specifically the flub-dub heart sound at the beginning. If you stipulate that the signal should be taken at your preamp's "tape out" output (and say if it's not), record a few of the beginning thumps and post pictures of those with some indication of what cartridge and electronics you used on both the digital and analog sides, you'd at least be able to say that when it got to that the tape out point your particular computer recording/display setup rendered it like so.

 

There are voice tracks in and out of polarity, and it is very easy to distinguish as the out of polarity tracks sound smeared and wobbly.

 

I think that's testing relative polarity (left and right channel the same). Absolute polarity (when waveform goes positive speaker goes out) is much harder to hear, and pretty much a dead issue if you're talking about modern multitracked recordings, where track to track and song to song can be different, let alone record to record. I have switches on my preamp which invert absolute polarity in both channels at will and I've never heard a difference. Someone with better hearing then I might be able to get it on specific one or two mic recordings.

 

AT 440mla


Shure m97xe


Opposite - both cartridges appear to be wired up correctly.