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strange SMSL M500 high 3rd harmonic

liu

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#1
I just got a brand new SMSL M500. it's the latest 1.7 firmware and 1.3 hardware version. (windows shows 2.06 in xmos utility).

The following measurements are done with computer -> USB-> M500 XLR output-> ADI-2 Pro input -> computer.

I use REW to generate the sine wave and plot the fft.

If I play sine wave from both L+R channels, or just the R channel, the FFT looks very normal:

Screen Shot 2021-04-22 at 17.24.56.png


However, if play sine wave only from the left channel, the third harmonics is 0.015%.

Screen Shot 2021-04-22 at 17.24.22.png


I tried different DACs (such as Topping's, or SMSL's M300), swapped cables, swapped L, R input channels, and can confirm this issue only happens with M500 left channel.

The issue only occurs when left channel is playing different audio compared to the right audio --- When L and R are both playing sine wave at the same volume, it's quite normal. When only the left channel is used, or when left is playing 90% volume and right is playing at 70% volume, the problem occurs.

Any guesses why it is like so?

And no, you won't find this test in either @amirm 's or @WolfX-700 's review.

Also, since SMSL SU-9 is basically the same hardware and software, an educated guess is this will happen in that device as well. though I'm not very sure.
 
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AnalogSteph

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#4
This one's weird. Something clearly is very unhappy there. I would suspect maybe a short or a bad solder joint in the signal path or on one opamp's power pins.

I would suggest testing the unbalanced and headphone outs next.
 
OP
L

liu

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Thread Starter #5
I would suggest testing the unbalanced and headphone outs next.
same thing on headphone out and unbalanced. The rca and HP actually get signal from the balanced --- the above tear down photo shows it very clearly.

the thing I don't quite understand is why it behaves correctly if (and only if) I play sine wave on both Left and Right channels with the same volume.
If left channel is fucked up it should be constantly broken.
 
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seki97

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#6
Mine is sw 1.7 and hw 1.3 as well... If I manage to open it I'll check if I have opas or lmes... but this is very bad.
 

Jimbob54

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#10
Guys, I just got a new device from Amazon and here's the result. They definitely fucked this up again. Now I can confirm all M500 devices suffer from this issue. View attachment 126161
Not sure I can agree with your conclusion there but there is something worth investigating further by smsl.

You can't say all based on 2 units
 
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liu

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Thread Starter #11
Not sure I can agree with your conclusion there but there is something worth investigating further by smsl.

You can't say all based on 2 units

here's the third unit, and I can see from the user's previous comments that it was bought July 2020. so SMSL has been cheating customers for a long time.
 

Jimbob54

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#12
here's the third unit, and I can see from the user's previous comments that it was bought July 2020. so SMSL has been cheating customers for a long time.
Meant the left channel issue. I can easily believe the op amps were swapped for a whole run or maybe forever.
 

Veri

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#13
Guys, I just got a new device from Amazon and here's the result. They definitely fucked this up again. Now I can confirm all M500 devices suffer from this issue. View attachment 126161
The interesting thing is still that when you measure both channels it doesn't happen, right? Can't this be a measurement artefact? Op-amp oddity?
 
OP
L

liu

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Thread Starter #14
The interesting thing is still that when you measure both channels it doesn't happen, right? Can't this be a measurement artefact? Op-amp oddity?
both xlr connectors are always connected so both are measured. the bug happens when I only play sine at the left channel vs both channel. see the following dialog

Screen Shot 2021-04-25 at 18.46.30.png

so yeah this is very easy to reproduce. anyone who has a M500 and audio interface can reproduce it.

I also tried the following --- letting right channel play a lower volume sine wave (such as -10dbfs) via this tool. same thing occurs as well. the device perform at its best when L=R. the larger the volume difference, the higher the 3rd harmonic is.
 

lizhuoyin

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#15
both xlr connectors are always connected so both are measured. the bug happens when I only play sine at the left channel vs both channel. see the following dialog

View attachment 126167

so yeah this is very easy to reproduce. anyone who has a M500 and audio interface can reproduce it.

I also tried the following --- letting right channel play a lower volume sine wave (such as -10dbfs) via this tool. same thing occurs as well. the device perform at its best when L=R. the larger the volume difference, the higher the 3rd harmonic is.
Is it REW? The UI looks different from mine. Do you update it to the latest?
 

solderdude

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#16
Can you do the following test on the L channel ?

L channel 1kHz and then slowly increase the 1kHz on the right channel while watching L channel ?
Also what happens if you have 1kHz on L only and then apply music or other freq. test signals on the other side ?

Does the same happen at say 1kHz L only but the 1kHz being -20dB or so ?

80dB 3rd harm. could be almost an audible thing.
When you listen to the 1kHz (only L channel) does it sound different from R channel only (via the same speaker) ?
 

solderdude

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#17
Is it REW? The UI looks different from mine. Do you update it to the latest?
When it is REW a simple L-R cable swap at the DAC output should make this clear.
Fairly certain liu will have done this already given post 1 where he mentioned this only happened with this particular model.
 
OP
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liu

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Thread Starter #18
Can you do the following test on the L channel ?
> L channel 1kHz and then slowly increase the 1kHz on the right channel while watching L channel ?

As I said above, "the device perform at its best when L=R. the larger the volume difference, the higher the 3rd harmonic is."

so if L = max and increase R from 0 to max, you'll see 3rd harmonic decrease over time





> Also what happens if you have 1kHz on L only and then apply music or other freq. test signals on the other side ?

Interesting

Here's L=sine and R = sqaure.


Screen Shot 2021-04-25 at 19.10.43.png


Here's L = sine and R = sine and both at the same volume, but different phase:
Screen Shot 2021-04-25 at 19.11.00.png

compared to L = sine and R = 0 below, you'll see different phase results to higher harmonics.

Screen Shot 2021-04-25 at 19.11.07.png


> Does the same happen at say 1kHz L only but the 1kHz being -20dB or so ?

Yes. Here I have the distortion panel on. you'll see lower the volume significantly reduced the 3rd THD.

Screen Shot 2021-04-25 at 19.15.20.png




Screen Shot 2021-04-25 at 19.15.08.png


> 80dB 3rd harm. could be almost an audible thing. When you listen to the 1kHz (only L channel) does it sound different from R channel only (via the same speaker) ?

I cannot do this experiment. SMSL devices are known for having higher output (to achieve good measuring results). My speaker is Genelec 8030C and even with the lowest sensitivity I cannot tune the volume above 15 (full is 40) on this device. With such low volume the thd is not high enough to be audible.
 
OP
L

liu

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Thread Starter #19
When it is REW a simple L-R cable swap at the DAC output shoulf make this clear. Fairly certain liu will have done this already.
yeah, I swapped cables already. I also swapped different devices (such as Topping's and SMSL's own latest gen M300). Pretty sure this only happens on M500 left channel.
 

Jimbob54

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#20
yeah, I swapped cables already. I also swapped different devices (such as Topping's and SMSL's own latest gen M300). Pretty sure this only happens on M500 left channel.
Not the first oddity with this dac. The thermal performance of the dac chip itself was wayward.
 
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