Measurements of LJM CS4398 DAC kit

[audio_tony]

Here are measurements of the LJM CS4398 DAC kit (still available on Ebay)

I built this around 2018 / 2019 IIRC.

The board has had some mods (specifics not shown here).

My test setup: Asus Xonar STX sound card with a self built buffer / gain box in front of that. Host PC is an Intel i7 running Windows 10 with 32G RAM and SSD - no mechanical disks or CDROM drive present.
I also use an Altor Audio Olivine-2 ADC, however the Asus Xonar was used these measurements.
Sound card input was set to 24bit/96kHz
I used an S.M.S.L. PO100AK as a USB to coax bridge, as the I do not use the limited USB input on board.
I used Arta for the measurements.
Output to DAC was set to 24/192kHz

My DAC assembled:

Board as advertised on Ebay:

THD 0dB

THD -3dB

THD -6dB

THD -30dB

THD -60dB

THD -90dB

Digital silence:

Frequency response (Arta sweep) - don't think this is right...

Frequency response (smoothed white noise):

Jitter:

THD vs Frequency:

 

[AnalogSteph]

THD 0dB

Kinda high. What are the analog supplies and opamp on this guy?

Frequency response (Arta sweep) - don't think this is right...

Why not? You've got a 50 dB vertical scale there, the default in RMAA would have been +4/-5 dB.

 

[audio_tony]

Kinda high. What are the analog supplies and opamp on this guy?

Supplies are 12-0-12 and opamp is NJM2043DD. Any other 'jelly bean' opamp yields the same result.

I have a couple of other CS4398 based DACs and they are the same at 0dB.

When I exported the response to a text (CSV) file it was suspiciously flat, i.e. all zeroes for the amplitude!

I have attached an example of the export. The response surely cannot be this flat...

 

[AnalogSteph]

I have a couple of other CS4398 based DACs and they are the same at 0dB.

Still, almost 0.01% THD+N is way short of chip specs. This guy should be able to achieve -98 dB worst-case. It's almost like there is some kind of oscillation or something, or the analog supply current is causing jitter?

I have attached an example of the export. The response surely cannot be this flat...

Why not? The chip itself has a combined filter FR spec of -0.01 to +0.01 dB (10 Hz to 20 kHz), plus whatever the output stage does. You're seeing -0.001 dB at 10 Hz to +0.011 dB at 20 kHz. Digital filter response itself at 96 kHz would be within 0.003 dB from 0 to 20 kHz.

 

[audio_tony]

Updated measurements.

Following the somewhat disappointing results (I was sure this had measured better previously) some further investigation found that Windows 10 was the issue here.
So I measured again using Linux.
As can be seen, the multitone and the -0.1dB results are hugely improved.

I guess my next quest is to re-measure all the CD players I did as well. Windows...