MC loading. Myth?

Discussion in 'Audio Hardware' started by Ingenieur, Dec 5, 2023.

  1. Ingenieur

    Ingenieur Just a dog looking for a home... Thread Starter

    Location:
    Back in PA
    This months Stereophile has a first page article on MC loading. The premise is it is not as critical as once thought. Phono amp SS Pass XP-27

    After reading it I had questions, lol.

    They measured response of pink noise at 300 and 47,000 Ohm. The only difference was magnitude, that is all they measured.

    So I wanted to see what else changed.
    I used a loading of 100 pF and their 300 and 47000 Ohms and calculated the impedance, magnitude and phase. The results are below.
    I left the calculations out, sorry, I know how much you guys love them. I only looked at the load. Next I'll look at load + cart.

    But the cart is a generator/source and the load determines its output.

    47 kOhm 20 to 20 kHz
    Magnitude 47000 to 40500, -1.3 dB, no much, likely not audible.
    Phase 0 to 30 deg, now that may be?

    300 Ohm
    Magnitude no change
    Phase 1/2 deg, nadda

    The cart will see an essentially pure resistive linear load at 300 Ohm.
    A non-linear reactive with 47000

    The 300 would be easier to drive, less phase distortion, etc.

    Not saying imo 300 to 500 or 40 to 100 does, but 300 to 47000? Likely

    graph, red = 300 Ohm
    [​IMG]

    Results
    [​IMG]
     
  2. TheVinylAddict

    TheVinylAddict Look what I found

    Location:
    AZ
    So you're asserting (with data in this case) that changes in loading (at least in the case or instance of what you measured) does nothing more than change the output in db (amplitude)? And other than amplitude the signals track identically, signifying that the simple act of turning the volume up or down would result in identical sound?

    Hmm.... interesting.
     
  3. SCM

    SCM Senior Member

    Location:
    Fl
    Nope...not a myth
     
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  4. Mitsuman

    Mitsuman Diamond Tone Junkie

    Location:
    Missouri
    Sorry, I’m missing the magic here. :shrug:
     
  5. Ingenieur

    Ingenieur Just a dog looking for a home... Thread Starter

    Location:
    Back in PA
    That was their implied assertion.

    Mine is it is more complicated, and the phase is impacted in extreme cases.
    The lower you can make the phase shift while keeping the load within the mfgs spec, the better.

    If you can make the load purely resistive, 0 deg phase the oscillating reactive power is minimized.
    Can't get the system to 0 because the cart is net inductive.

    The best may be -x at the load and +x at the cart.
    System net 0 deg.
    I need to look at that
    Xc and Xl cancel.
    Time to change lp's lol

    back :)
    Mono week
    Jazz at the Oblerlin off
    Workin' with the Miles Davis Quintet on

    cart load 10 Ohm 22 uH
    20 Hz, 10.00 /0.016 deg, obviously all R 10 Ohm

    20,000 Hz 10.385 / 15.6 deg, 10.00 Ohm R, X = 2.8 Ohm

    X for load at 20 Hz ~ 20,600, R 34,900

    It should not be a big factor
     
    Last edited: Dec 5, 2023
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  6. TheVinylAddict

    TheVinylAddict Look what I found

    Location:
    AZ
    @Ingenieur - what cartridge(s) did you test, and thinking you probably used more than one?
     
  7. TheVinylAddict

    TheVinylAddict Look what I found

    Location:
    AZ
    Yes, any experiment :) is only as good as the controls and the variables - that was my next question - are you measuring everything that is impacted?

    @Ampexed
     
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  8. TheVinylAddict

    TheVinylAddict Look what I found

    Location:
    AZ
    Ah, you added this part after I posted my last two posts... I've often wondered about what you're kicking around here. I'll keep an open mind as it's where I need more data.... :) Interesting topic.
     
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  9. Davey

    Davey NP: Chihei Hatakeyama ~ Mirage (2017 LP)

    Location:
    SF Bay Area, USA
    Yea, we've shown the frequency response stays the same under different loads in the past here, I did one plot below with my AT-OC9XML at both 121 ohms and 47kohms showing only the expected change in volume. But as you say, it is more complex on both the cartridge and preamp sides, there are compliance changes at the cartridge and filter changes at the preamp that may also impact overload performance. Possibly distortion changes, and maybe other cartridge parameters are affected too. And if you switch between load values without compensating for the volume change, you may also perceive a frequency balance change since our hearing is more sensitive to higher frequencies. And if you add transformers in the mix, hehe, it gets way more complicated. But not sure anyone will have their mind changed by your findings, still an interesting diversion, kind of like the record weight thread :)


    [​IMG]

    The Technics SL-1200 GAE/G/GR general questions thread
     
    Last edited: Dec 5, 2023
  10. Ingenieur

    Ingenieur Just a dog looking for a home... Thread Starter

    Location:
    Back in PA
    I did not test, they did Ortofon Windfel Ti

    I used the numbers from my AT33PTGii for the calculations
     
  11. Ingenieur

    Ingenieur Just a dog looking for a home... Thread Starter

    Location:
    Back in PA
    I only ran the numbers because the assertion sounded 'off'. Not based on MC carts, but EE in general.

    The issue is the load X/C C is much, much, larger than cart X with L

    20,000 vs 2.8, so that would seem to imply it can't be manipulated for phase.
    But lower R can be.

    I've drawn no conclusions, only wanted to see the impact on the other primary signal component, phase.

    the resonance frequency is so high that it can't mechanical be reproduced nor is it audible if it were.
     
  12. TheVinylAddict

    TheVinylAddict Look what I found

    Location:
    AZ
    Thanks. Yes, it appears there's more going on agree it's not as simple as the test made it appear.

    BTW, your title / OP made it a little confusing for me at least as to what you were asserting vs he test conclusion :).... but I see now and still keeping an open mind!
     
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  13. Ampexed

    Ampexed Forum Resident

    Location:
    Santa Fe, NM
    This is the frequency response / level changes with my AT ART9Xi with loadings of 1000 Ohms, 100 Ohms, and 10 Ohms. I can do a 1kHz distortion FFT of all these if you really want, but I'm not in the mood to do any additional work unless there's something in it for me. o_O

    Looks like just level differences to me...

    BTW, these were done with REW - see how useful this program is beyond room measurements? :agree:

    [​IMG]
     
  14. Catcher10

    Catcher10 I like records, and Prog...duh

    Have not read the article yet.....but fine whatever they say. At end of day, for me, changing from my current loading of 475 ohms to 47K or even 100K changes the sound experience for me negatively. 475 ohms gives me insane resolution and dynamics, end of story for me.
     
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  15. TheVinylAddict

    TheVinylAddict Look what I found

    Location:
    AZ
    Vintage or modern mono? :)
     
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  16. Ingenieur

    Ingenieur Just a dog looking for a home... Thread Starter

    Location:
    Back in PA
    Modern
    AT33Mono
    imo excellent
    Much better than the mono switch
    Much quieter too
     
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  17. TheVinylAddict

    TheVinylAddict Look what I found

    Location:
    AZ
    If you paid the thread cover charge, there's a raffle, maybe you'll win something.

    Yes, it does appear.... seeing a theme here.
    Are you posing the question because your ears tell you different?:D

    Because these results would change a lot of rules of thumb, tribal knowledge and paradigms, no? Are loading changes, in all cartridges, just the higher db elixir....?

    What's it mean?
     
  18. Ampexed

    Ampexed Forum Resident

    Location:
    Santa Fe, NM
    My feeling is that people who are hearing a difference are mainly reacting to the level difference, and as you know, our ears are very non-linear to changes in level (Fletcher-Munson curves).

    That being said, when the loading on my cartridge is towards the lowest (lower than recommended), I can hear dynamic compression to a slight degree. With my years in recording and using compressors of all types, I'm very sensitive to hearing the effects and artifacts of compression. When the loading is within the recommended range, the only difference I hear is one of level.

    That there is an impact on level dynamics isn't so surprising since the generator within the cartridge is being damped by the lower resistance. This could probably be tested by playing square waves (the Ortofon test disc I have has a quasi-square wave band) and noting the rise times.
     
    Last edited: Dec 5, 2023
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  19. chervokas

    chervokas Senior Member

    Well one wouldn't expect the LCR resonance and rolloff effects to anywhere near the audible range with a low inductance MC. Was anyone really expecting FR changes in the audible range from MC loading? The R loading should effect the amplitude of ringing at the LCR resonant frequency, but with MC that'll be in the RF range.
     
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  20. Ingenieur

    Ingenieur Just a dog looking for a home... Thread Starter

    Location:
    Back in PA
    Interesting
    The difference between 10 and the other 2 vary with frequency. If purely R that would not happen. The reactive component changes phase which impacts magnitude.

    I would not do this since the delta is so small but one way to optimize might be:
    Start high and decrease in small steps, if the difference shrinks (a null sum)
    When it reaches the minimum/most consistent, and starts to increase. Use the previous value.
     
  21. Ampexed

    Ampexed Forum Resident

    Location:
    Santa Fe, NM
    My every day loading is set by the reflective impedance of the moving magnet input stage my SUT is seeing and is around 470 ohms. I have no reason to change it. I just did that graph showing the effect of extreme 10 Ohm loading because I could. The minimum recommended load by Audio Technica is 100 ohms for my cartridge.
     
    Last edited: Dec 5, 2023
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  22. Ingenieur

    Ingenieur Just a dog looking for a home... Thread Starter

    Location:
    Back in PA
    Mine is fixed based on gain.
    A 2 winding SUT feeds the MM section
    1:8 is rated 40 Ohm, measures ~60-70 Ohm
    1:24 rated 2.5 Ohm, measures 7 Ohm

    I use the lower gain. I like it.
     
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  23. pacvr

    pacvr Forum Resident

    Location:
    Maryland
    The issue with loading may be with the preamp. In the TI literature for its preamp opamp AN-346 High-Performance Audio Applications of The LM833 (Rev. D) "In addition to the amplitude response errors (which can be made small through careful design), the lack of a continued rolloff can cause distortion in later stages of the audio system by allowing high frequency signals from the pickup cartridge to pass through the phono equalizer without sufficient attenuation. This is generally not a problem with moving magnet cartridges, since they are usually severely band-limited above 20 kHz due to the electrical resonance of cartridge inductance and preamp input capacitance. Moving coil cartridges, however, have very low inductance, and can produce significant output at frequencies as high as 150 kHz. If a subsequent preamplifier stage or power amplifier suffers from distortion caused by slew-rate limitations, these ultrasonic signals can cause distortion of the audio signal even though the signals actually causing the distortion are inaudible." This concept of the cartridge loading being beneficial for preamps with insufficient high frequency design margin is commonly addressed by Ralph Karsten of Atma-Sphere.

    Otherwise, if you wish to play around with the numbers, and you want to see what a single node/pole LCR filter looks like, use this calculator, just plug in the values and it will perform the transfer function and plot the bode diagram along with other functions showing you the resonant peak (and cut-off frequency) Low-Pass Filter Design Tool (okawa-denshi.jp).
     
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  24. TheVinylAddict

    TheVinylAddict Look what I found

    Location:
    AZ
    The same Ralph Karsten who is a member here?
     
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  25. Ingenieur

    Ingenieur Just a dog looking for a home... Thread Starter

    Location:
    Back in PA
    That is one advantage of an SUT. The L helps as a low pass.
    Mine -3 dB at 40 kHz , -6 at 80 Hz as far as I can tell from tests.
     
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