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Measurements Of Generic ES9028Q2M DAC Board

March Audio

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#1
I have wondered for a while what these generic Chinese DAC boards found on ebay are actually like. On face value can they really be that bad?

First one is a ES9028Q2M based board. It has single ended, balanced and headphone outputs. Audio and digital sections appear to have separate power supplies driven from a 2x 15V and 1x 9V transformer. This board only accepts I2S input but there are a plethora of xmos based boards that will do the job of conversion from USB. It comes with a short ribbon cable for connection. Note there is no onboard clock with this board, MCLK has to be provided from the USB to i2s board.

I bought this from Audiophonics simply due to the massive and rather random delivery times from Chinese Ebay vendors (not to mention Cinese New Year delay) where it can be found much cheaper.

https://www.audiophonics.fr/en/diy-...alanced-dsd-1x-lt1963-regulators-p-12355.html

1.jpg


2.jpg


Single Ended Outputs

0dBFS - Output is low at 1.44V rms. 2nd and 3rd harmonics are fairly high.
upload_2018-3-2_14-59-23.png


-6dBFS - harmonic distortion drops significantly
upload_2018-3-2_15-0-50.png


-60dbFS - Noise floor drops revealing a spread of harmonics, but these are at a low level
upload_2018-3-2_15-7-35.png


-90.31dBFS (24BIT)- Quite a noisy waveform with low frequency (probably 50Hz mains) modulation
upload_2018-3-2_15-10-15.png


24 Bit J-Test - Not the cleanest but no significant jitter
upload_2018-3-2_15-14-40.png


IMD SMPTE - Again not the cleanest
upload_2018-3-2_15-17-18.png

upload_2018-3-2_15-18-1.png


FR and imaging
upload_2018-3-2_15-19-25.png


Linearity - Not good, bombs after -115dB
upload_2018-3-2_15-44-49.png


Overall conclusion from the single ended output is its unimpressive, but not that bad. Considering I have seen this for as low as $30 US on ebay then you have to put it in perspective.

I will test the balanced later and see if that offers improvement.
 
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March Audio

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#2
Balanced Output

odBFS - Thats not expected, the output voltage is lower at 1.3Vrms! Harmonics seem similar however low frequency noise has reduced.
upload_2018-3-2_17-0-54.png


-6dBFS
upload_2018-3-2_17-2-7.png


-60dBFS - Some odd things going on in the noise floor but no harmonics as found in SE.
upload_2018-3-2_17-3-15.png


-90.31dB 24 bit Waveform - cleaner and no LF modulation
upload_2018-3-2_17-44-33.png


Jtest
upload_2018-3-2_17-5-42.png


IMD SMTP
upload_2018-3-2_17-6-33.png

upload_2018-3-2_17-6-58.png


Linearity - much better than single ended.
upload_2018-3-2_17-17-10.png


Overall a marginal improvement with balanced. I havent followed the circuit through but I am guessing its configured to take the balanced DAC output and I to V convert with the first dual opa amp (5532) and convert to single ended with the subsequent single 5534 op amp. I wonder if the circuit can be finessed?

Listening impressions? A very quick listen through my Oppo PM1 cans it aint terrible, lacks a bit of detail but surprisingly listenable. It sounds softer than my Chord Mojo.
 
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DonH56

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#6
Not a lot of difference between balanced and unbalanced after a very quick skim. Balanced should cancel even-order distortion but not do much to odd order so some of the distortion measurements are "interesting". The drop in signal level is also odd. I suspect the conversion circuit though the static linearity improved.
 

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