Measurements of LJM CS4398 USB DAC With NJM4580D

[kozard]

In case it helps someone else in a purchasing decision I have enclosed measurements of the LJM CS4398 USB DAC with my choice of NJM4580D op amp installed.

The distortion is pretty much at the limit of my SB0490 to measure. It is still worth measuring because it could help detect a major layout or power supply issue.

I do see a strong roll off at 20 kHz and some ripple. Can anyone comment on that? Expected? Anyone else measure the same? The filter is stock except for the NJM4580D.

I use it with my project amplifiers with the volume potentiometer at maximum and using software control of volume. I think that sounds better than setting the DAC at maximum/full scale and then controlling the amplifier with the potentiometer.


If anyone knows how to get the EMU 1820m working with Windows 10 then I could remeasure with a better ADC.




I would appreciate any advice/help/comments on improving the measurements. One of my hobby goals for 2021 is to add good quantitative measurements to my experiments. (Especially evaluation of my project amplifiers.) Next I am going to try to figure out how to measure the CIRMECH CS4398 (did not measure properly with the SPDIF output of the SB0490) and then one of my project power amplifiers.

 

[kozard]

I was looking at the output filter recommendation in the datasheet and I found the filter shown below in the first attached image.

Since it referenced application note AN-48 I looked at that. However AN-48 has a very different filter as shown in the second attached image.

Can anyone help explain to me which is best to use? (And why the datasheet references AN-48 and then AN-48 has a totally different set of values?) What am I missing?

 

[Rick Deckard]

The output filters in fig 12 and fig 5 are for two different
dacs. cs4398 and cs4329 respectively.
I would use the filter in fig 12 for a cs4398 dac.

 

[kozard]

Ok. It is just confusing when the CS4398 datasheet refers to the output filter in AN-48 and then that filter in AN-48 is the wrong one. (And is instead for a different DAC.)


Page 21 of CS4398 Datasheet:

The Cirrus Logic application note “Design Notes for a 2-Pole Filter with Differential Input” (AN48) discusses the second-order Butterworth filter and differential to single-ended converter topology that was implemented on the CS4398 evaluation board, CDB4398, as seen in Figure 12.