Massdrop THX AAA 789 and Schiit Jotunheim Measurements

Discussion in 'Headphone Amplifier Measurements' started by purr1n, Nov 17, 2018.

  1. purr1n

    purr1n Finding his inner redneck

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    Jot vs THX AAA 789.png

    Observations
    1. Both are excellent measuring amps at these realistic power levels and loads. Red is THX AAA 789. Blue is Jotunheim. Purple is where the plots intersect.
    2. Jotunheim has a slightly higher noise floor. At -140db, no one will hear this.
    3. THX AAA 789 has a few harmonic spikes from power mains hum. At -125db, no one will hear this.
    4. Distortion characteristics at 1kHz look extremely similar.
    Notes:
    1. AverLAB output set to 8.23dBu. I figured this would be representative of consumer DAC output levels.
    2. The volume knob was adjusted accordingly to get -3.0dBu (within +/-0.1db) on the balanced outputs.
    3. The load was 330ohms to approximate to the nominal impedance of Sennheiser HD6## headphones.
    4. Both L and R channels are driven.
    5. The THX AAA 789 exhibited a sharp AC mains spike near -100db when the Jotenheim chassis was placed on top of it. I figured the big power transformer on the Jotunheim messes with a few things. I wouldn't worry about it. You can't hear the hum at -100db unless you are Amir. If you are super paranoid about measurements, then don't place any magnetics (transformers) near the THX AAA 789 chassis.
     
    Last edited: Nov 17, 2018
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  2. Elnrik

    Elnrik Super Friendly

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    Are you saying these amps do things I won't be able to hear? WTH is the point then?

    After seeing this, I cannot recommend
     
  3. purr1n

    purr1n Finding his inner redneck

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    LOL, both of these amps would be worthy of instrumentation gear 10-15 years ago. They do sound different per subjective impressions here: https://www.superbestaudiofriends.org/index.php?threads/massdrop-x-thx-aaa-789.5852/

    If there is a lesson to be learned, don't fall for hype over measurements. Good measurements are important, but only to a certain extent. And as I've said before, the THX AAA 789 does deserve a bit more notice than it has on SBAF.
     
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  4. Roget

    Roget Rando

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    @purrin: How do you explain this? The distortion is much higher here.

    Schiit Jotenheim DAC dashboard as is measurement.png
     
  5. yotacowboy

    yotacowboy McRibs Kind of Guy

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    I'm gonna go out on a limb and guess the power cables behind Amir's setup look like a rats nest.
     
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  6. SoupRKnowva

    SoupRKnowva Official SBAF South Korean Ambassador - Friend

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    >Yotunheim[sic]
    >DAC as is

    I guess the fact that he measuring the amplifier only doesn’t mean anything to you?

    Also, as Marv mentioned, things being near each other can have a great influence on measurements, a fact that he openly disclosed when he could have just posted the worse measurements for the THX amp, since were all Schiit schills here.

    Also also, who the fuck knows where this random image came from?
     
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  7. purr1n

    purr1n Finding his inner redneck

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    I believe that for that particular measurement, Amir may have used the built-in multibit DAC card, which does not measure well. The measurement is fair when considering the Jotunheim / multibit DAC card combo as an AIO. However, it does not reflect the amplifier's performance. I believe Amir used a 300 ohm load with that measurement.

    Here is an equivalent measurement (but with similar 330 ohm load) running 8.23dBu input (2Vrms) and setting the volume so that gain is zero - same 2Vrms output.

    Jotunheim 2Vrms input. 0 gain into 330 ohm load.
    Schiit Jot 1kHz 8.23dBu 0 gain.png

    The unfortunate reality is that Amir likes to speak half-truths, enough truth to shrug off lawsuits, but also not enough to mislead those who do not read carefully. This is the second time in a few days that new posters have associated Schiit gear with "bad measurements". It's important to set the record straight.
     
    Last edited: Nov 17, 2018
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  8. purr1n

    purr1n Finding his inner redneck

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    Here is the equivalent for the THX AAA 789

    THX AAA 789 2Vrms input. 0 gain into 330 ohm load.
    THX AAA 789 1kHz 8.23dBu 0 gain.png

    Observations:
    • THX AAA 789 noise floor is lower, but unless you listen to music at levels with 150db (actually more like 200db) peaks, you are not going to notice.
    • The lower noise floor reveals more of the distortion characteristics of the THX AAA 789. The more visible spikes past 3-4kHz do not mean the THX AAA 789 has more distortion.
    • We get more insight into the distortion characteristics of these amps. The Jotunheim has declining distortion at the 2nd, 3rd, and 5th harmonics. The THX AAA 789 has a declining distortion at the 2nd, 3rd, 4th harmonics.
    • Distortion is similarly low for both amps.
    • There is some AC mains noise and related harmonics, but not significant at -125db.
     
    Last edited: Nov 17, 2018
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  9. purr1n

    purr1n Finding his inner redneck

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    Of course, nothing on SBAF is replete without a bit of drama:

    drama.png
     
  10. SoupRKnowva

    SoupRKnowva Official SBAF South Korean Ambassador - Friend

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    That’s embarrassing, someone at THX or Massdrop should shut him up before he does actual damage to the product.
     
  11. yotacowboy

    yotacowboy McRibs Kind of Guy

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    "789 has MUCH lower noise, distortion, and intermod performance"

    Of course! 'cause i can reliably A-B/X the difference between a -125db and -135db noisefloor. All caps is completely necessary for measurements under 120db below full signal. That should be some sort of standard. Proclamations of N measurements greater than 20db below human hearing threshold should be all caps, if not bolded and italicized. Even greater reverence given to those written in comic sans.
     
  12. Elnrik

    Elnrik Super Friendly

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    I'll explain it.

    Amir couldn't measure his own ass with both hands and a yard stick.
     
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  13. purr1n

    purr1n Finding his inner redneck

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    Well, if you want to be silly about it, you could be like Amir and bitch about the "skirt" at the base of the 1kHz test tone. Let's not go there. Both amps measure excellently. I'll run some more tests later, maybe with a live headphone instead of a resistor! The new frontier. Maybe magic smoke. Muahahahaha.
     
    Last edited: Nov 17, 2018
  14. Cspirou

    Cspirou They call me Sparky

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    Very dumb. Amirites would just do that crap for him and he wouldn't have to get his hands dirty.

    https://www.instagram.com/p/BqOP8RiA1Ts/?utm_source=ig_share_sheet&igshid=hs6jhucbulud
     
    Last edited: Nov 17, 2018
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  15. Roget

    Roget Rando

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    Oh OK. That makes sense. I didn't know that the built-in DAC was limiting the Jot. What would you recommend for a DAC? What did you use to get your measurements?
     
  16. purr1n

    purr1n Finding his inner redneck

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    If you care about measurements, the DS card or any DS DAC with opamps are going to measure well. Heck, throw an SDAC, ODAC, Topping, Modi, etc. there. They all measure close enough to each other.

    I used the AverLAB's signal generator to feed both amps. Come to think of it, the above measurements might be limited by the AverLab's signal generator.
     
    Last edited: Nov 17, 2018
  17. purr1n

    purr1n Finding his inner redneck

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    A large part of D2 and D3 is likely from the generator. The higher D4 on from the THX AAA 789 might actually be a sign that it measures worse than the Jotunheim in terms of THD. However, the THX AAA 789 takes the cake in terms of the noise floor for this last set of measurements at 2Vrms. However, 2Vrms into a Sennheiser HD600 will blow your ears out if not melt the voice coils.

    With amps, I like to rely on measurements that reflect realistic use, and then push things a bit to better see differences. I dislike measurements for the sake of measurements. The -3dBu used in the first set of measurements is 0.548 Vrms, which is deafening loud into the HD600.
     
  18. atomicbob

    atomicbob dScope Yoda

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    I would like to address the issue of requesting explanations for random measurements such as this one pulled from the internet. Without context, this graph is meaningless.

    1. Where is the picture depicting measurement setup? It matters, especially for looking at power supply noise over 85 dB below stimulus, which in this case amounts to approximately 112 uV. Not hard to find that much noise with a ground issue present.
    2. What was the test load? 30R, 300R or ?? It matters when evaluating harmonic distortion.
    3. Which input / output combination was used? Single ended will often measure higher in THD+N than Balanced.

    A comprehensive set of measurements on the Jotunheim may be found here:
    https://superbestaudiofriends.org/index.php?threads/jotunheim-technical-measurements.2760/

    Comprehensive measurement for many amps may be found here:
    https://superbestaudiofriends.org/index.php?forums/headphone-amplifier-measurements.13/

    And finally, my pet peeve, why measurement numbers are just short of worthless here:
    https://superbestaudiofriends.org/i...-of-6-amps-thd-n-and-thd-specifications.6194/
     
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  19. Negura

    Negura Friend

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    Is there a way to measure crosstalk. The published spec for Jot seems very low. Crosstalk: >-70dB, 20 Hz-20KHz.
     
  20. atomicbob

    atomicbob dScope Yoda

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    In the post directly above yours this can be found:

    A comprehensive set of measurements on the Jotunheim may be found here:
    https://superbestaudiofriends.org/index.php?threads/jotunheim-technical-measurements.2760/

    In that comprehensive set of measurements is both the simple numerical roll-up of crosstalk and the much more informative graphs of crosstalk vs frequency for each channel. Four combinations of balanced / SE at both 30R and 300R are provided.
     
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