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ebay SPDIF dac "CS8416 + CS4398" only  - worth a try?
ebay SPDIF dac "CS8416 + CS4398" only  - worth a try?
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Old 22nd September 2014, 09:12 AM   #11
Stefan0815 is offline Stefan0815  Germany
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Hello Charly,
If i had read your thread before, i would't have bought the PCB.

I have got an idea why this dac performes so bad.
In the attachment is the suggested "minimalistic" filter.
As you can see, there is a second cap preventing the DAC driving a permanent DC current.
Adding this cap would be a easy tweak (all in all i'd like to modificate SMD more than DIL)

To you have the possibility to check, if the PCB has the chematics of the datasheet?
I can count 4 ceramic caps per channel and 6 resistors. The part's count does fit with it.

My second Idea is, that those ceramic caps are so bad, that they couse the "outstanding" disturtion.

My PCB will arrive in a few weeks and my goal is to tweak this little pcb to the datasheet performance (even then, jitter performance won't be very good, but for such a cheap dac?)
Attached Images
File Type: png 2014-09-22 11_06_35-4398cs.fm - CS4398_F1.png (10.5 KB, 562 views)

Last edited by Stefan0815; 22nd September 2014 at 09:18 AM.
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Old 22nd September 2014, 04:58 PM   #12
CharlieLaub is offline CharlieLaub  United States
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ebay SPDIF dac "CS8416 + CS4398" only  - worth a try?
Sorry I can't trace the PCB. It seems to be more than 2 layer.

In a similar thread on another forum some on-board SMD caps were identified as the main culprit of the rising distortion at higher input levels. I bought another board with the same ICs but using film caps as the output filter and it has a relatively flat distortion profile. I think that the builder just wanted to make a small and cheap DAC.

As I pointed out, if you used this only for low frequencies there is no problem and performance is fine in that application.
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Old 30th September 2014, 06:14 PM   #13
Stefan0815 is offline Stefan0815  Germany
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My DAC arrived very fast.
I traced the Analogue Filter chematics for the Right Channel.

At least that, there is no CAP in the positive DAC output does stress the DAC with a permanent 3k Load.

A little bit tweaking, and it's the original one.
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File Type: png dacFilter.png (26.3 KB, 508 views)

Last edited by Stefan0815; 30th September 2014 at 06:38 PM.
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Old 4th October 2014, 02:45 AM   #14
CharlieLaub is offline CharlieLaub  United States
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ebay SPDIF dac &quot;CS8416 + CS4398&quot; only  - worth a try?
Quote:
Originally Posted by Stefan0815 View Post
My DAC arrived very fast.
I traced the Analogue Filter chematics for the Right Channel.

At least that, there is no CAP in the positive DAC output does stress the DAC with a permanent 3k Load.

A little bit tweaking, and it's the original one.
What do you add/change? Sorry I could not follow it. Can you give more details please?
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Old 8th October 2014, 03:00 PM   #15
Stefan0815 is offline Stefan0815  Germany
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Sorry for my very bad written last post!

If you compare the original schematics from CS and the ebay dac schematics you will notice that both are using the same topology.
There are slight differences:

The CS one does have a second elec cap to avoid DC current. I will add this cap.
The values for parts seems strange in the CS chematics, but they are making sense for low noise.

The values of the resistors are "hard to find" (farnell does have those values but i'd like to go to a local store!). So i give a try with other values:

R40-> 1,58k ----> 1,6k
R35-> 698 ----> 680R
R41 -> 1,27k ----> 1k2
R37 -> 604R ----> 619R
R38 -> 267R ----> 270R
R36 -> 487R ----> 470R
R2 --> 560R ---->100R

This gives a CMRR which is better than the 1% resistor tolerance.

What's harder to find are good npo caps with the suggestet values in SMD. So i will go for MKS02 RM2,5 Caps.

I choose:

C44 -> 1n8 ---> 2n2
C43 -> 6n8 ---> 6n8
C39 -> 4n7 ---> 4n7
C1 (this number seems to be wrong) -> 18n ---> 22n

All Parts are for one channel, the other one is mirror inverted on the board.

This will give you not a perfect filter response, but we are talking about a cheep dac, so i don't like to spend too much on presision parts.

Parts are around 5€ in Germany

I haven't finished the modification untill now, but i will do the mod on the weekend.

Last edited by Stefan0815; 8th October 2014 at 03:03 PM.
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Old 8th October 2014, 03:24 PM   #16
CharlieLaub is offline CharlieLaub  United States
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ebay SPDIF dac &quot;CS8416 + CS4398&quot; only  - worth a try?
I'm interested in seeing the results of your experiment.

My problem with the DAC was only the performance as signal level approached digital 0dB (maximum output). Within about 10dB of this, the distortion performance had a rising character that exceeded 0.1% distortion by 20kHz dominated by odd order products. But at lower levels (e.g. -20dB) the DAC had more of a flat distortion profile with THD levels well below 0.01% except for a slight rise of 3rd order above 10kHz. You can see my measurements in post#9 in this thread.

I got some feedback that this distortion behavior is characteristic of non-NP0 type ceramic caps. So it's good that you are replacing the SMD caps with better types (MKS) in addition to adding the elcap.

Can you do some distortion testing after adding the MKS caps and before adding the elcap? It would be interesting to see the relative influence from these two modifications on any improvements that occur...
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Old 8th October 2014, 09:32 PM   #17
Stefan0815 is offline Stefan0815  Germany
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I don't know if i had the time to make those tests.
The Problem is that i don't have a good ADC at home. In university lab i have acsess to simmilar gear, but in the moment everyone is in stress there.

If you do some modifications on the resistors, the elcap is necessary because the DAC can only drive 1k and will be saturated by the DC current.

I think changing the caps is the best (and most easy) modification. Ill try to measure the original ones for you.
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Old 28th October 2014, 06:39 PM   #18
Stefan0815 is offline Stefan0815  Germany
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Hello out there!
It takes a long time for me to get a running Setup.
In the moment i use the ADC of a Terratec TS22 Soundcard (i think it was a AKM Chipset).

Because i had a OPA 1642 in stock, i changed the NE 5532.
Aditionally i added a few Tantals on the board and bypassed the output Caps with foil ones.

The first screenshot was measured with 2vpp

The second screenshot was shoot with a load of 100Ohm (with a output resistor of 270Ohm). You get around 10db less output voltage but the THD did not rise at all.

I think the THD is limited by the ADC and think i am on specs now.

Can anyone help me out with the right grounding?
In the moment the Case is grounded with the chinch connectors to anal. ground. The Spdif input went trought a transformer and isn't earthed at all. The Powersupply is not conneced to the case.
Attached Images
File Type: png Spectrum.png (227.3 KB, 399 views)
File Type: png Spectrum2.png (145.3 KB, 376 views)
File Type: jpg 2014-10-28 19.42.47.jpg (463.1 KB, 396 views)

Last edited by Stefan0815; 28th October 2014 at 06:51 PM.
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Old 28th October 2014, 10:58 PM   #19
Stefan0815 is offline Stefan0815  Germany
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I did another modification on the DAC:

I power it from a single wall mart supply and noticed that the ripple on the positive voltage supply was around 500mV with the typical peaks (If you supply it with a dual supply the ripple decrease, but even 250mV are a lot!).

I decided to use a CRC Network with aditional 2200uf and a 10Ohm Resistor. That takes the powersupply ripple down to 50mV with much less peaks in it.
This help's to remove the 50Hz Humm on the output.
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Old 30th October 2014, 03:25 AM   #20
CharlieLaub is offline CharlieLaub  United States
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ebay SPDIF dac &quot;CS8416 + CS4398&quot; only  - worth a try?
Quote:
Originally Posted by Stefan0815 View Post
Hello out there!
It takes a long time for me to get a running Setup.
In the moment i use the ADC of a Terratec TS22 Soundcard (i think it was a AKM Chipset).

Because i had a OPA 1642 in stock, i changed the NE 5532.
Aditionally i added a few Tantals on the board and bypassed the output Caps with foil ones.

The first screenshot was measured with 2vpp

The second screenshot was shoot with a load of 100Ohm (with a output resistor of 270Ohm). You get around 10db less output voltage but the THD did not rise at all.

I think the THD is limited by the ADC and think i am on specs now.

Can anyone help me out with the right grounding?
In the moment the Case is grounded with the chinch connectors to anal. ground. The Spdif input went trought a transformer and isn't earthed at all. The Powersupply is not conneced to the case.
Good job! This is definitely an improvement on the performance.

Usually you would ground the case to earth ground, but with a wall wart power supply that isn't available. Using the PS ground like you are doing is second best. I'm pretty sure that the spdif input should not be earthed.
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