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SMSL SP200: Do We Get Golden Samples For Review?

amirm

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#1
I recently reviewed the SMSL SP200 THX headphone amplifier and gave it very high marks for excellence in performance. Given that this product was not yet available, I accepted the opportunity to review. Same happens with offers from other manufacturers. Invariably someone after the review wonders if I have received a "golden sample," i.e. a handpicked unit to measure well. My answer is that the chances of that is very low but that if there is some doubt, people should send another one and we can verify. Well, that has happened. A member ordered a SP200 and kindly sent it to me for evaluation.

For this assessment, I am just performing some spot checks as opposed to re-running all the tests. If there are differences, these tests should easily show them.

Let's start with our dashboard view using the same settings as the review unit:

SMSL SP200 Production Version Dashboard.png


SINAD which represents noise and distortion relative to our source signal is only 1 dB down. I see variations like this and more in products I test. There is always some variability with respect to temperature, environment, run to run variation in measurement, etc. So this is definitely within the accuracy limit of our measurements.

What I can't explain is the spectrum of distortion products changed. Here it is from the review unit:
1572730349058.png


We are still below -130 dB but the role of 2nd and 3rd harmonics has changed.

Next I tested the signal to noise ratio for the same input and output level:

SMSL SP200 Production Version Signal to Noise Ratio.png


We see a 1.7 dB difference which likely the reason SINAD changed similar amount. Again, nothing to worry about.

Let's see how our power curve relative to THD+N looks with 300 ohm load:

SMSL SP200 Production Version Power into 300 ohm.png


Performance is as identical as you can get. Both high and low gain product the same power and very low distortion and noise.

The one element that I thought would have variation would be the analog volume control. So I tested channel balance:

SMSL SP200 Production Version Channel Balance.png


This is quite different than the review sample. First, the level would not change for quite a while and once it started to change, it fell apart a lot sooner than the review unit. You can only get 30 dB of attenuation before channel balance becomes extreme relative to 70 dB before.

Hard to tell if this is an outlier, typical of these analog controls, the one I got was hand picked or what. If you are going to use sensitive IEMs, this may be an issue for you.

Conclusions
I see little evidence of SMSL having picked a special unit to send me. Performance is as superb as the review unit. Volume control has some issues but as mentioned, I think there are other explanations for this than a golden sample.

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Noob

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#2
As an advocate for controling volume with a variable output DAC, analog potentiometers are no issue for me. I reccomend everyone get a DAC with volume control so that you can leave your amp at max and have perfect channel balance.
 

Veri

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#3
As an advocate for controling volume with a variable output DAC, analog potentiometers are no issue for me. I reccomend everyone get a DAC with volume control so that you can leave your amp at max and have perfect channel balance.
That's a smart way around that particular issue, indeed :)
 

Labjr

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#4
I'd still like to see a stepped attenuator as an option. A single resistor in the signal path is better than any pot.
 

Toku

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#5
I think it is acceptable from the quality level of the potentiometers used.
However, the sample may have been selected from a product with good potentiometer characteristics.
It's not just SMSL, but any manufacturer will want to see the product better. That is very natural.
 
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AnalogDE

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#7
Any manufacturer will have access to test data so there wouldn’t really be a big effort to find the best testing unit.
 

August

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#8
The emphasis of the first harmonic and the second harmonic are interchanged.confused:D
 

DDF

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#10
I'm not the least bit surprised at this. A well run manufacturer would probably double check that review units are functioning properly, but to actually cherry pick? QC would have to be pretty bad for that to make an appreciable difference!
Cheap pots typically have appreciable sample to sample variation in channel tracking matching. Given how well engineered this unit seems to be, its very likely that smsl know the mfg variance of the pots they use and they'd be taking a big risk not checking the pot before sending a unit to asr for test.

Years ago when I bought a Gilmore Lite, the pot tracking was very poor, like this unit. The mfg didn't hesitate to send me a hand picked pot to swap in, acknowledging the variance between units.
 
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Shadrach

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#11
Mod edit: ouch! I edited this post instead of replying to it by accident. Typing on my phone in bed....

Before anyone goes into outrage mode, I'm not suggesting amim is complicit in any of what follows.
That seems ri be half your thesis though. :(

This is supposed to be a science based forum and in reality the OP doesn't actually prove anything. A smart marketing person would arrange just such a comparison with a comparable unit.
I believe sly marketing of a similar nature was what encouraged Amazon to start To make this post mean anything the puchaser should be identifiable, a copy of a purchase ticket should be available showing date of purchase and an independent body do the test.
The unit was purchased from third party seller and drop shipped to me. The purchase is a senior member of the forum and has sent me gear before. I am 100% confident he has no connection with any seller or manufacturer.

If you are going to doubt the above you might as well question what you are for lunch.

As for your Amazon example how do you know they are not faking entire reviews including the verified purchase tag? If you doubt me you should doubt them too.
 
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KSTR

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#12
What I can't explain is the spectrum of distortion products changed.
[...]
We are still below -130 dB but the role of 2nd and 3rd harmonics has changed.
Nothing to worry about and completely inside normal item-to-item deviations.
Mind you, a distortion profile is complex thing, the various stages in a product might contribute their harmonics with all different phase angles. Vector sums, that is, and therefore anything can happen from plain scalar summing to partial cancelling. This makes the spectrum look somewhat unstable.
Also, if the analyzer residuals are less than 20dB below the DUT, this vector summing instablity must be taken into account as well. Your AP of course clears that mark.
 
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#13
I'm surprised with the result too.
For the manufacturers, it is easy to test each components and select the components closest to the specification to create a Golden Sample for reviews. What if they use the same PCB and BOM sheet, but use worse components for mass production? It is impossible for customers to distinguish the differences.
 

amirm

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#14
Mod edit: ouch! I edited this post instead of replying to it by accident. Typing on my phone in bed....


That seems ri be half your thesis though. :(


The unit was purchased from third party seller and drop shipped to me. The purchase is a senior member of the forum and has sent me gear before. I am 100% confident he has no connection with any seller or manufacturer.

If you are going to doubt the above you might as well question what you are for lunch.

As for your Amazon example how do you know they are not faking entire reviews including the verified purchase tag? If you doubt me you should doubt them too.
So to be clear this was my response to poster.
 
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#15
As an advocate for controling volume with a variable output DAC, analog potentiometers are no issue for me. I reccomend everyone get a DAC with volume control so that you can leave your amp at max and have perfect channel balance.
Granted, I know next to nothing about electronics, but the idea of leaving an amp on high gain at max volume all the time scares me.
 

Veri

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#16
Granted, I know next to nothing about electronics, but the idea of leaving an amp on high gain at max volume all the time scares me.
Unless you are using IEMs where you don't want "accidents" to blow up your earphones or ears, there's nothing dangerous about it.
Then again I would roll with low gain at max volume (this is +6dB over unity gain which is for me, plenty).
 

Jimster480

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#17
Do you have the original? maybe you can do a teardown on both units and see if there is a different pot?
 
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#18
Do you have the original? maybe you can do a teardown on both units and see if there is a different pot?
So to be clear this was my response to poster.
Dear Jimster480, Yes you are right! we use B type Pot on the mass product, the one we sent to amir was a A type, but they are the same series pot. the performance is the same! just the volume position is changed!
 
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amirm

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#19
Do you have the original? maybe you can do a teardown on both units and see if there is a different pot?
I don't have permission to open the original. And the owner is returning the new one so don't want to open that either.
 
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