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ES9038Q2M Board
ES9038Q2M Board
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Old 3rd January 2018, 10:00 PM   #61
JensH is offline JensH  Denmark
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ES9038Q2M Board
Victors I/V circuit looks similar to what I used, except that I didn't convert the output to a single ended signal. And I used different op-amps and slightly different resistor values.
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Old 3rd January 2018, 10:13 PM   #62
DPH is offline DPH  United States
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In either case, it clearly seems like your I/V isn't the culprit in the rather mediocre performance but the 9038 board, seeing as Victor is still getting better all-in performance (~-115 dB on the 3rd harmonic at 0 dBfs).

Still nice knowing these guys perform better in current mode. Also, the measurements are appreciated!
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Old 3rd January 2018, 10:40 PM   #63
JensH is offline JensH  Denmark
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ES9038Q2M Board
I think that ESS generally recommends current mode, without being specific about the differences.

The main source of noise in the original circuit seems to be the relatively high resistor values in the filter/buffer. So the dynamic range of the original design gets nowhere near the performance possible with the DAC chip.

Perhaps I should try the current mode with e.g. the LME49720 to see if it will be better than the LME49990 for this.
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Old 3rd January 2018, 11:05 PM   #64
DPH is offline DPH  United States
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It might be, but at this level, it's pretty much impossible to tell outside of empirically. Paradoxically with your 1.26 K feedback network, I'm getting the 49720 as the lower noise option, albeit very slightly (3.56 vs 3.66). (If I made a bonehead about the current noise contribution, do correct me)

I don't have the respective current outputs of the 9018k2m vs the 9038q2m either. I'm assuming they're the same, in which case, you have 1.5x the gain.
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Old 4th January 2018, 08:12 AM   #65
freezebox is offline freezebox  Germany
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I did not get it..is current or voltage mode just pending on the output circuit following the DAC output or do I need to set it somehow in the controller for the DAC chip?


JensH, the 2 resistors I see on the picture in your report (thanks for publishing it!)are a V-devider for the the 1,65V to feed to the yellow wire?
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Old 4th January 2018, 08:45 AM   #66
terry22 is offline terry22
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thanks
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Old 4th January 2018, 08:56 AM   #67
JensH is offline JensH  Denmark
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ES9038Q2M Board
Yes, current mode or voltage mode is determined by the circuit connected to the output of the DAC. Some DAC's are intended for current mode, e.g. some of the high-end converters from TI and some DAC's are intended for voltage mode, e.g. converters from AKM and Cirrus Logic. The ESS DAC's can typically be used in either current mode or voltage mode.

In current mode the output is held at a fixed voltage, typically provided by an op-amp with the inverting input directly connected to the output of the DAC (one op-amp for each polarity). The non-inverting input is connected to a reference voltage, in this case 1.65 V (half of the 3.3 V supply). The feedback will make sure that the DAC output is held at the same voltage as the reference voltage. The current through the DAC output will vary depending on the audio signal applied to the DAC.

In voltage mode a high impedance filter/buffer stage is connected to the output of the DAC. So the DAC output will have some voltage swing in this case.

Yes, I used two resistors and a tantalum capacitor to make a 1.65 V reference.
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Old 4th January 2018, 09:32 AM   #68
terry22 is offline terry22
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Quote:
Originally Posted by pet547 View Post
I own this NE5532 replacement: HDAM Double differential circuit Fully symmetrical circuit Double op amp replace NE5532 LME49720 MUS02 OPA2604-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group

I am waiting for the delivery of my power supply and then I want to test the board with this replacement.

@freezebox: Please can you tell me (us) which DC blocking caps are to be bridged and which resistors are to be removed. The board revision is VR1.04.

Thanks!
Hi, do you own the old or the new board?
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Old 4th January 2018, 10:53 AM   #69
freezebox is offline freezebox  Germany
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Hello JensH,


Thank you for your Explanation! I could also use a dual op-amp for each channel as well, right? And I need the DC blocker circuit at the output as in victors shematic due to DC offset? What C and R did you use?
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Old 4th January 2018, 11:32 AM   #70
androa76 is offline androa76  Slovenia
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Hi Jensh.
Interesting measurements.
Can you show a schematic of your output stage in current mode?
Voltage mode was original like on board?
Thank you.
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