Cartridge Alignment: Setting Azimuth with a PC and Soundcard

Discussion in 'Vinyl Nutjob World: Turntable and Related Gear' started by purr1n, Apr 17, 2016.

  1. purr1n

    purr1n On vacation

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    If you have some money to blow, just get one of these: https://www.gcaudio.com/cgi-bin/store/showProduct.cgi?id=636

    From http://www.gcaudio.com/resources/howtos/cartbasics.html


    Azimuth: Even more critical (in my opinion) to proper set-up than VTA, is cartridge azimuth. Unfortunately VTA gets all the press, therefore many people are not aware of the importance of this adjustment. What is azimuth? Looking at the cartridge body from the front, it is the left to right tilt of the cartridge body. Contrary to popular belief, azimuth is not necessarily correct with the sides of the cartridge body are perpendicular to the record surface. What we're actually looking for is the correct relationship of the stylus to the groove. Unfortunately, the vast majority of styli are not mounted perpendicular to the bottom of the cartridge body, thus making azimuth set-up by sight alone erroneous. And with the current trend toward decreasing stylus size, even seeing the stylus without the aid of magnification borders on the improbable. The "eyeball" or "mirror" method should only be employed if other more sophisticated methods are unavailable.

    I set the azimuth on my cartridge with a PC and a QA400. You don't need a QA400. A soundcard with free RTA/FFT software will do. You can use jDFT: https://people.kth.se/~johk/jdft/ or other free software. A test LP with separate 1kHz left and right tones is also required: http://www.musicdirect.com/p-8523-ultimate-analog-test-lp-analogue-productinos-test-vinyl-lp.aspx

    The procedure is to set the azimuth so that crosstalk (bleed from one channel to the other) for each channel is the same. That is, for the reference level left channel 1kHz tone , the right channel output should be the same as the left channel output for the right channel 1kHz reference level tone. Crosstalk is going to be pretty bad on turntables, on the order of 25-35db, so this will be easy see in a spectrum analyzer.

    Here is the crosstalk (RED) on the the right channel, bled in from the left channel 1kHz reference level tone.
    azi L.png

    Here is the crosstalk (YELLOW) on the the left channel, bled in from the right channel 1kHz reference level tone.
    azi R.png

    IMG_20160417_160925351.jpg
    Above is a phono of the cartridge with the VPI azimuth alignment rod after alignment using the above method. Note that the stylus is not quite mounted perpendicular to the bottom of the cartridge body! I had previously "eyeballed" it with the VPI rod, and it turned out after measurement that the left and right crosstalk signals were off about 4-5db!

    Supposedly, azimuth alignment is more crucial to the cartridges with the Micro Line, Micro Ridge, Shibata, SAS type contact tips because the needle goes deeper into the grooves. I can't attest to this, but I can say that after an afternoon of experimentation, setting azimuth using this method yielded a much more stable center image and a more focused precise sound.
     
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    Last edited: Apr 17, 2016
  2. NekoAudio

    NekoAudio Acquaintance

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    Yep. Azimuth is super, super important. Azimuth calibration on my reference table changed No Doubt's "Tragic Kingdom" from a sloppy incoherent mess into the awesome music it is supposed to be.

    But I'd like to chime in and say only addressing crosstalk may not be good enough. If the crosstalk and phase line up perfectly at the minima then it'll work out, but Feickert's example measurements show sometimes crosstalk and phase don't. In which case, you can be better off with slightly higher crosstalk in order to get matching phase.
     
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  3. purr1n

    purr1n On vacation

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    The phase for azimuth is the one thing I'm still scratching my head around. It shouldn't be difficult to check phase with ARTA's Time Record view; however, can't phase also be tweaked with cartridge offset angle (zenith)? And wouldn't phase be inherently slightly off here and there from tracking error (on traditional, not linear tracking arms)?

    Another way to check phase would be the use of the 1kHz signal out-of-phase on track 4 on the Analog Productions Test LP. The output can be summed and the minimum signal would be the ideal.

    I'm trying to find solutions that don't require the payment of $400 for Fonzimeters or $500 for Dr. VonDoom's software. This stuff shouldn't cost that much and the only reason it does is because of the wealth dichotomy of vinyl users (either semi-poor or ultra rich).

    One last solution might be a USB microscope to check the stylus (as opposed to the cartridge body).
     
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    Last edited: Apr 18, 2016
  4. Vastx

    Vastx Facebook Friend

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    Er... What's azimuth phase?
    In case you're wandering, I googled it already :oops:
     
  5. purr1n

    purr1n On vacation

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    Changing azimuth will affect LR phase, LR/RL crosstalk and LR balance / level. This gets to be a clusterfuck because so many things are interrelated and also because it's normal for cartridges to be off 1 db or so between L and R channels. Would be interesting to see real life examples of the relationships between azimuth, phase, and crosstalk.
     
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  6. NekoAudio

    NekoAudio Acquaintance

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    It's hard for me to know for sure but I assume any sort of movement of the cartridge can affect phase, including azimuth. But if you want to keep the needle lined up straight (based on the protractors) and that still doesn't give you proper phase and crosstalk then you have to adjust azimuth.

    Azimuth is like the clockwise and counterclockwise rotation of the cartridge, if you're looking at it head on. Some arms let you mount the cartridge and then rotate the arm itself to adjust azimuth. Other arms don't rotate and you have to try adjusting the two screws attaching the cartridge to the tonearm, letting out one and pulling in the other, in order to adjust azimuth.

    You should be able to look at phase using a two-channel oscilloscope, I imagine. For a given frequency, peak sum between the channels would be matched phase, or A-B would be zero at matched phase. The ease of everything using Adjust+ makes it worth it for me. But yes, it is relatively expensive.
     
  7. Dr. Higgs

    Dr. Higgs Boson - Member

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    This tip is great! I thought the soundstage seemed off with my new cart, and when I tried your method using the level meter in ARTA I saw that the crosstalk in the right channel was awful. Just got it adjusted to within approx .5-1db in both channels and it sounds like everything has snapped into place.
     
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  8. slowsound

    slowsound Acquaintance

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    Are AP 200 G LPs of good quality?

    I keep reading QPR 200 G tends to be dished and sometimes off centre.
     
  9. purr1n

    purr1n On vacation

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    It's surprising how off perpendicular cartridges, even up to several hundred dollars, can be. Ask you can see, my 2M Black had to be tilted slightly right for the needle to be perpendicular to the record. My Ortofon Cadenza Bronze was spot on though.
     
  10. Mr.Sneis

    Mr.Sneis Friend

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    VTF and anti-skate are gimmies but so many of the consumer level tables do not have VTA much less Azimuth adjustment capability :( They indeed are crucial IME but damn is it expensive to buy the "proper" tools.
     
  11. JoshMorr

    JoshMorr Friend

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    Ok this is a pretty basic question, but how would one connect their laptop to a turntable for this analysis? I was thinking a usb sound interface similair to Focusrite Scarlett Solo which could also double up as mic interface. Then a RCA to 1/4" cable to connect the two?
     
  12. Dr. Higgs

    Dr. Higgs Boson - Member

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    I just used an RCA to 3.5mm cable and plugged straight into my laptop's mic input. Be warned that some laptop mic inputs will only record in mono, which means you'll need a different interface to measure both channels.
     
  13. purr1n

    purr1n On vacation

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    You can use the Focusrite. Just needed RCA to phono adapters.
     
  14. Chris F

    Chris F Boyz 4 Now Fanatic - Friend

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    Here here is a good trick I've been using to do azimuth quick and dirty. I've found it very useful while breaking in my new cart as I have been changing parameters on a semi weekly basis to see how the sound changes. The catch is that you need a digital recorder (or software) that can do peak hold for each channel in realtime. I think all standalone ones do (the DA-3000 has a whole submenu for it); not sure about software.

    Anyhow:
    - Pull out a mono record that you are certain was cut properly (I'm using the AP re-issue of "Masterpieces by Ellington")
    - Set the peak hold on your recorder to 3s
    - Play the record and watch the peak hold values; if the channels are constantly within 0.5db (or whatever the balance spec for your cart is) you are good else adjust until they are

    Note that this only gets you good channel balance and ignores phase and crosstalk. However, if balance is bang on crosstalk should also be close to ideal since they are directly tied together. Phase I am not so sure about; this is a new measurement to me (wrt to phono carts) and I need to do experiments/understand more.
     
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  15. Wfojas

    Wfojas Friend

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    I forgot about this method, its been so long, lol. But i do remember that if you wire one channel out of phase, a balanced output will give you the overall lowest sound. Peak holds on meters are better, though I agree.
     
  16. Cspirou

    Cspirou They call me Sparky

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  17. Wfojas

    Wfojas Friend

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    That's how Mint protractors are made, actually. So assuming there are no sizing discrepancies from file to print, he should be done.
     
  18. bazelio

    bazelio Friend

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    I fucked around with cart alignment tonight using a digital oscilloscope called Bitscope. I bought the Bitscope for other breadboard stuff, but now find it pretty damn useful for cartridge setup. Previously I'd only use mirrored protractors and Fonzimeters.

    Cutting to the chase: Mirrored protractors (like the Mint) and Fonzimeters get you close, but you can do better. Anti-skate can be dialed in quantitatively. The Ultimate Analogue test LP is really useful. My rig does sound better after doing this.

    The Jerry-rigged setup looks like this. A piece of metal flashing with two RCA chassis connectors and a speaker binding post for a ground wire connection. I came from the cart, in to a SUT, and then into the scope. The signal coming off the cart directly is lower than than noise floor of my scope. The distortion properties of this sut are acceptably low.

    [​IMG]

    First look, phase and amplitude using test LP track 1, 1 kHz left + right. To start, phase and amplitude were off. I tweaked zenith a bit to bring phase in line. Then I found an azimuth setting which didn't disturb the phase but brought L + R to the same amplitude. This was the result (L + R channels both displayed).

    Oscilloscope waveform:

    [​IMG]

    Vectorscope (a perfect result is a line with slope of 1 (45 degrees), no or minimal ellipse:

    [​IMG]

    Pretty damn good. When I started, I could clearly see an elliptical vectorscope shape, and non-overlapped waveforms in the o'scope. The vectorscope is really useful for visualizing aberrations.

    Next, crosstalk. Here we screw with azimuth to dial this in.

    Left 1 KHz, right channel no signal.

    Oscilloscope waveform:

    [​IMG]

    Vectorscope (a perfect result is a horizontal line, no or minimal ellipse shape):

    [​IMG]

    Pretty good. This one was a bit more of an ellipse at the start. Throughout the track, you'll see the ellipse opening and closing a bit, but it's pretty stable, and almost perfectly horizontal.

    Right 1KHz, left channel no signal.

    Oscilloscope waveform:

    [​IMG]

    This one is visually worse in the waveform. How about the vectorscope (a perfect result is a vertical line, no or minimal ellipse shape):

    [​IMG]

    Some crosstalk from right to the left channel is clearly visible. The vectorscope is tilted, and the o'scope shows ripple as well.

    Looking at the frequency domain...

    Right channel:

    [​IMG]

    Left channel:

    [​IMG]

    So, about 30dB of separation. Not bad really. It was about 28dB when I started, so it slightly improved. What I found is that I could tilt azimuth quite a bit more to improve crosstalk in this direction. However, then I would start to see both phase and amplitude get much worse. So rather than going all out for crosstalk, I left a dB or maybe two on the table as a tradeoff. It's still pretty good. The Fonzimeter was a bit misleading - i.e. I would have (and previously) did over-correct for crosstalk....

    All in all, this is easy (and fun) and relatively low cost. I'll probably sell the Fonzimeter now, and the Bitscope will be paid for if I do.

    Oh, and I forgot to capture the waveforms from the test LP, side 2, track 1 for anti-skate. But this was equally easy to visualize. I had previously set the anti-skate too high and one channel was breaking up earlier than the other. Now both channels are clean up to the highest level. It took about 5 minutes to find the sweet spot.
     
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  19. Cspirou

    Cspirou They call me Sparky

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    ^^^

    Bookmarked!
     
  20. lehmanhill

    lehmanhill Almost "Made"

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    Big thanks to Baselio. I have a similar digital scope and got nice results using your approach. The best part is that it is straightforward and understandable.

    In the area of confessing my own mistakes to keep others from repeating them, make sure your wires are not interfering with horizontal motion of the tonearm. I read somewhere that you should be able to balance the tonearm so it doesn't rest on the record and be able to easily move the tonearm across the record surface by blowing on it.

    I missed that step and I can tell you that your ability to adjust the tonearm is pretty much gone if there is drag on the horizontal movement. You can still see the measurements on the scope, but adjustment isn't predictable, even possible.
     

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