CHANGSTAR: Audiophile Headphone Reviews and Early 90s Style BBS

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Author Topic: Amp measurements: Obj2, Magni 2, Vali, Studio  (Read 3016 times)

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Solderdude

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Re: Amp measurements: Obj2, Magni 2, Vali, Studio
« Reply #10 on: July 26, 2015, 10:23:36 AM »

Thanks for measuring this Marv.

Kuddos for posting them as most high-end amp manufacturers never post plots like these as they are hard to 'defend' given how many people adhere to nothing but 'superb' measurement values.

It's actually pretty good for this type of amp design.
Not worried about everything below -70dB myself.
When you look at the spectra of real instruments you often find the 2nd, 3rd harmonics are just 10 to 20dB below or even above the fundamentals so I don't worry about harmonics usually unless they are really high order ones that are high in levels as well.

I think one has to 'fear' more for IM.

What I find funny though is that most people worry (and/or claim) that everything above -100dB is potentially audible (especially in DACs) and subsequently amplify those signals with amps that 'add' god knows what to their signals.
But IMO if one likes what one hears who cares how it measures as it is all about personal enjoyment of music/sound and as this amp appears to deliver who cares.

Would be fun to have a 'full' set of measurements on some of the better sounding gear though.
Willing to bet that NO relation to subjective reports will ever be found though.

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aive

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Re: Amp measurements: Obj2, Magni 2, Vali, Studio
« Reply #11 on: July 26, 2015, 02:27:11 PM »

What I find funny though is that most people worry (and/or claim) that everything above -100dB is potentially audible (especially in DACs) and subsequently amplify those signals with amps that 'add' god knows what to their signals.

Pretty sure quite a few ppl on this forum have made that claim inc Marv, unless I misinterpreted his claim to be able to hear ~18 bits dynamic range? Not a jab, just sayin.....

I have no idea what my audible threshold is so can't say either way practically speaking , although the engineer in me is naturally bias towards less distortion...
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Marvey

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Re: Amp measurements: Obj2, Magni 2, Vali, Studio
« Reply #12 on: July 26, 2015, 03:30:31 PM »

Pretty sure quite a few ppl on this forum have made that claim inc Marv, unless I misinterpreted his claim to be able to hear ~18 bits dynamic range? Not a jab, just sayin.....


The bit-depth with DACs and associated noise floor with those bit-depths is a totally different story from distortion:
  • Digital hard clips at 0db, so with good uncompressed masters, we are unlikely to see much or any of the codewords near 0db. This in essence reduces the effective bit-depth of a recording.
  • In my own experience with true 24-bit recordings, I found that decimating down to 18-bits to be no different from original 24-bits, and 18-bits to be possibly better than 16-bits. It's possible that 18-bits sounded better because of less quantization error.
  • Finally, we are talking about distortion signals. Distortion signals are likely to be masked by the fundamentals which are playing much louder. It's important to not confuse the ability to hear dynamic range with the ability to hear distortion.
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Marvey

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Re: Amp measurements: Obj2, Magni 2, Vali, Studio
« Reply #13 on: July 26, 2015, 03:59:30 PM »

What I find funny though is that most people worry (and/or claim) that everything above -100dB is potentially audible (especially in DACs) and subsequently amplify those signals with amps that 'add' god knows what to their signals.

This is probably one of the most harmful things that came from nwavguy. Misunderstandings or obsessive focus from laymen and sadly "engineers" (or other self-appointed experts who cite various unrelated credentials) on getting the best results from a suite of five or six measurements. Results that far far surpass what these very same people can actually hear.

Willing to bet that NO relation to subjective reports will ever be found though.

I would say there is quite a bit of correlation - if and only if you know what specifically to listen for*. For the EC Studio, Craig and I, and to a lesser extent Anaxilus, went through almost a dozen interstage transformers. We listened and measured (the transformers). It's no accident that the best of the bunch had the best distortion characteristics - mainly in the bass - where distortion tends to be highest and most audible.

However, the notion that distortion on a FFT spectrum plot is the end-all-be-all is completely ridiculous. We simply need to do a thought exercise:

The distortion of transducers is a magnitude or two (or three) higher than that of amplifiers. A headphone's distortion will completely dominate a amp's distortion on an FFT spectrum plot. If one wanted to be a hard-ass and "objective" about measurements, then amp distortion measurements (at least from most amps) really don't matter. If one wanted to be true to measurements, one cannot cherry pick ... it should be that the measurements that matter most are those coming out from the transducer as part of the total system.

*I've always maintained that measurements must be correlated to subjective experience and not be considered in a vacuum - measurements for measurement's sake. Jason @ Schiit said the same thing in his measurements post on HF.
« Last Edit: July 26, 2015, 04:18:56 PM by marvey »
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Marvey

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Re: Amp measurements: Obj2, Magni 2, Vali, Studio
« Reply #14 on: July 28, 2015, 03:28:56 AM »

More measurements. Again 100 ohm load at ~0.6V. /10 probes. Just getting some baselines. Ultimately, I'd like to take the measurements at 300ohm and 30 ohm loads which represent Sennheiser and typical orthos respectively. We at Changstar should try to develop some baseline measurements which are reflective of typical conditions experienced in the hobby.

The Studio at 20Hz and 40Hz. I feel that tube amps biggest disadvantage compared to solid-state is bass performance. Solid state typically has better bass definition and articulation, at least to my ears. Keep in mind that The Studio has uber (near $1000 / pr.) custom interstage transformers with nano-crystalline cores (which did measure better than all the other interstages we tested).

What's interesting is that we see more 3rd order harmonic distortion (-51db) for the 20Hz tone. Second order distortion is -58db down. For the 40Hz tone, the 2nd harmonic is -65db (0.06%) The 3rd order is a little bit higher -57db (0.14%). Wait a minute, aren't tube amps supposed to have a high level of "pleasant sounding" even order harmonics? The moral of the story is that we shouldn't overgeneralize.  FWIW, all distortion sucks to my ears, including even order. Whoever said even order harmonic distortion is pleasing should be shot.

I really doubt most people will be able to hear these small levels of distortion in the bass. Those who have heard The Studio know how good the bass quality is on the amp. Finally, it should be noted that 99% of music has very little or rolled off energy below 40Hz.
« Last Edit: July 28, 2015, 03:50:06 AM by marvey »
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Marvey

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Re: Amp measurements: Obj2, Magni 2, Vali, Studio
« Reply #15 on: July 28, 2015, 03:37:08 AM »

Vali (hybrid amp) bass distortion. Same conditions. 20Hz and 40Hz for comparison.

For the 20Hz tone, Vali is slightly worse in 2nd order, but much better for 3rd order compared to The Studio. Same situation for the 40Hz tone, although 2nd order on the Studio is significantly better -65db vs -54db (Vali). Vali does have much lower 3rd order, about 33db better!

Succinctly, The Studio does have better 2nd order performance than the Vali, but is worse in the higher order distortions.
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Marvey

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Re: Amp measurements: Obj2, Magni 2, Vali, Studio
« Reply #16 on: July 28, 2015, 03:41:18 AM »

Magni 2 here.

As we can see Magni 2 destroys anything prior with a tube. The interesting thing is that even order distortion is non-existent.


Now the important questions are:
  • What levels of distortion at 20Hz and 40Hz can we actually hear?
  • Does bass distortion, even from the tube amps, even matter if the distortion from the transducers are going to dominate (HD800, HD600, etc.)
P.S. 100 ohms is a odd load. Going go run these tests again with ~300 ohm load which should cover a lot of the Sennheiser headphones.
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schiit

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Re: Amp measurements: Obj2, Magni 2, Vali, Studio
« Reply #17 on: July 28, 2015, 03:57:33 AM »

Holy crap, that's brave, posting 20Hz measurements out of a transformer-coupled tube amp! Transformers are most disadvantaged in the bass (just check some bad transformer-coupled designs for bass distortion, holy moly.) The Studio is daaaaammmmnnnn impressive.

I expect midband measurements to be really amazing.
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Anaxilus

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Re: Amp measurements: Obj2, Magni 2, Vali, Studio
« Reply #18 on: July 28, 2015, 04:16:53 AM »

How relevant is tube rolling and tube condition to these? Would be cool for people to see how/if different tubes alter what you've shown and whether there would be a subjective correlation.
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Re: Amp measurements: Obj2, Magni 2, Vali, Studio
« Reply #19 on: July 28, 2015, 04:26:35 AM »

From what I remember on the Torpedo measurements (which is not the same as the Vali and the Studio), different tubes had indeed different characteristics. The 6J6Ws had less overall distortion than the E90CCs, but a little more higher order distortion in the upper frequencies.

I would expect similar in other systems. However, obviously is not always possible to tube roll.

Also, those are indeed fairly good measurements for the Studio given the Vali reference, which I don't think uses transformers in the topology.
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