ESS THD ‘Hump’ Investigation

[solderdude]

Is the same opamp used in the IV stage ?
Is the same DAC chip output current flowing into the IV stage in both schematics ?
Is the IV stage running on a higher voltage in the sgd1 ?
The IV converter in the Tone board doubles as 2V output stage or is it going into a not shown circuit ?

 

[Herbert]

1-no But should an ideal opamp have almost no load on the DACs output?
2-we should assume yes
3- a current DAC-output needs to be tamed, does'nt it?
4-The answer to your question is linked schematic.

 

[Herbert]

The new Khadas Tone Pro2 is humpless:

https://www.audiosciencereview.com/forum/index.php?threads/khadas-tone2-pro-review-dac-amp.20684/

But this time, Khadas did not publish the schematics, correct?
AFAIK though it has balanced output, they use the same DAC and opamps.
If so it would be interesting to know the resistor values...

 

[somebodyelse]

The new Khadas Tone Pro2 is humpless:

https://www.audiosciencereview.com/forum/index.php?threads/khadas-tone2-pro-review-dac-amp.20684/

But this time, Khadas did not publish the schematics, correct?
AFAIK though it has balanced output, they use the same DAC and opamps.
If so it would be interesting to know the resistor values...

No schematics yet, but there's a folder ready for them so perhaps they'll turn up soon?
https://dl.khadas.com/Hardware/Tone2/

 

[Veri]

No schematics yet, but there's a folder ready for them so perhaps they'll turn up soon?
https://dl.khadas.com/Hardware/Tone2/

They changed designed from Tone 1 though (who is behind SONCOZ).
Maybe they don't share in-depth schematics anymore.

 

[Herbert]

We´ll see. But is it confirmed that the same DAC and opamps are used.
In the Tone1 it was a formerly not known "audio"opamp from a chinese manufacturer...

 

[somebodyelse]

They changed designed from Tone 1 though (who is behind SONCOZ).
Maybe they don't share in-depth schematics anymore.

Perhaps, but it'll be a change of direction if they don't - I think every other product of theirs has schematics available. It's one of the things that distinguishes them in a positive way from some of their competitors, so I hope they continue. Maybe @Gouwa can comment?

 

[ShiZo]

Was this ever figured out?

 

[Herbert]

Not yet. Khadas has not published schematics of the Khadas Tone Pro2.
Assuming that they still use the same opamps it should be fairly easy
to change the resistor values. A pity as I still have a sealed v1 that I would like to modify.
I do not need volume control or selectable filters or balanced out...

 

[Herbert]

Took some minutes to compare images from the Tone1 with Tone 2.
Different board layout, different Opamps.
So I guess no hump-solution on this path...

 

[syn08]

Was reading this thread and duly noted people claiming the IMD/THD hump is present only in the ES9038QM2 DACs, while the ES9038PRO is missing this ESS signature feature https://www.audiosciencereview.com/forum/index.php?threads/ess-thd-‘hump’-investigation.5752/page-6 I also see Amir measured a few commercial ES9038PRO products (Melokin DA9.1, etc...) and did not find the hump too (although this result was not consistent?!).

Well, I am sad to report that the ES9038PRO chip has the hump as big and fat as other ESS DAC chips, see attached THD measurement (X axis is in dBFS). This is an ES9038PRO in mono mode, balanced output, half of the IV stage simplified schematic (removed decouplings, etc... for less clutter) is also attached.

I'll try to see if the known hump counter-measure work for the ES9038PRO as well, I ould suspect they do.

So all ESS DAC products are affected by this issue, and they did nothing to fix it in subsequent revisited designs. Dissapointing, but what else is not disappointing about ESS? Unfortunately, after the AKM factory demise, they have a quasi monopoly on the high end DAC market.

 

[mansr]

Unfortunately, after the AKM factory demise, they have a quasi monopoly on the high end DAC market.

Cirrus and TI both make perfectly adequate DAC chips too.

 

[syn08]

Cirrus and TI both make perfectly adequate DAC chips too.

Not for an instrumentation project I am working on.

 

[deafenears]

Was reading this thread and duly noted people claiming the IMD/THD hump is present only in the ES9038QM2 DACs, while the ES9038PRO is missing this ESS signature feature https://www.audiosciencereview.com/forum/index.php?threads/ess-thd-‘hump’-investigation.5752/page-6 I also see Amir measured a few commercial ES9038PRO products (Melokin DA9.1, etc...) and did not find the hump too (although this result was not consistent?!).

Somewhere mentioned, either in this thread or elsewhere, the 9038 PRO suffers from this too. Examples are the Sabaj D5 and SMSL VMV D1.

 

[syn08]

Somewhere mentioned, either in this thread or elsewhere, the 9038 PRO suffers from this too. Examples are the Sabaj D5 and SMSL VMV D1.

Yep, my measured THD+N appears a smidge better, but otherwise it tells the same story

 

[chris719]

Cirrus and TI both make perfectly adequate DAC chips too.

Cirrus is also having supply problems on some products. Probably due demand from former AKM customers. I thought UMC was their foundry also... and they may be busy with more important things these days.

 

[syn08]

...and the ES9038PRO hump is gone .

The solution was almost trivial: someone reported on this forum (don't have the link, it was only casually mentioned to me) launching the hypothesis that a change in the Vcm could address the ES9038PRO "hump" issue. This turned out to be 100% true. Also noted from the ES9038PRO ESS reference board schematic that they use a Vcm=1V instead of the obvious guess of AVCC/2=1.65V.

My implementation with the ES9038PRO in mono mode, 2x4channels in parallel, then summed up, 49.9ohm as I/V resistor. You can see above the results for Vcm=1.65V. Lowering Vcm leads to shifting the "hump" towards higher input levels, to the sweet spot of Vcm=0.68V, where the hump is gone for good. Attached are the THD and THD+N measurements.

I hav no idea why lowering the Vcm eliminates the "hump", not sure if Vcm=0.68V is the sweet spot for any configuration (the ESS reference board suggests it is not, since they use Vcm=1V, but for 8 independent channels) but mostly I have no idea if the same almost trivial method would apply to the ES9038Q2M. If anybody has any ideas how/why Vcm affects so strongly the distortion profile, I am all ears.

-112dB THD+N and -123dB THD, this is one good DAC A shot of my ES9038PRO test board (one channel only installed, shown in a digital loop with my own ADC implementation) is also attached below.

 

[Veri]

Very nice.. there appears to be some saturation at the end of the sweep though

 

[KSTR]

If anybody has any ideas how/why Vcm affects so strongly the distortion profile, I am all ears.

We would need the distortion profiles vs. level first for any sort of educated guesses. Do only harmonic levels change, are non-harmonic spuriae popping up (like seen on any AKM), is there any change in noise floor (correlated), does digital DC bias change anything, etc?

Excellent work and shame on ESS for their non-communication/non-information policy on this blatant issue... now AKM also doesn't have everything covered in their datasheets but still much better than ESS.

 

[TheTalbotHound]

Cirrus and TI both make perfectly adequate DAC chips too.

Cirrus sure, but i haven't seen much high performing stuff using TI chips, if any. Would be interesting to see someone like topping try their hand at a TI based design, like they did on the D30Pro with Cirrus.