CS4398 capacitor vs. op-amp out - diyAudio
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Old 25th April 2012, 11:52 AM   #1
Ciorny is offline Ciorny  Austria
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Default CS4398 capacitor vs. op-amp out

Hello

Have a modified Gigawork CS4398 DAC with OPA627 (no buffer-stage) as a sum amplifier & without couple-cap (disconnected now)....see attachment

I would not like to come here deeper into my modifications, but ask myself whether a passive analogous out itself would be better listens than with a op-amp?

I have thought the following to me:

CS4398 + pin --> resistor 1K --> cap 2.2 --> + RCA --> amplifier (16K)

CS4398 - pin --> resistor 1K --> - RCA (ground)

Any thought?

Thanx
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Old 25th April 2012, 01:41 PM   #2
Ryssen is offline Ryssen  Sweden
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In my opinion a cap is better,but I dont think you need the 1K resistor.
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Old 25th April 2012, 03:07 PM   #3
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Quote:
Originally Posted by Ciorny View Post
Hello

Have a modified Gigawork CS4398 DAC with OPA627 (no buffer-stage) as a sum amplifier & without couple-cap (disconnected now)....see attachment

I would not like to come here deeper into my modifications, but ask myself whether a passive analogous out itself would be better listens than with a op-amp?

I have thought the following to me:

CS4398 + pin --> resistor 1K --> cap 2.2 --> + RCA --> amplifier (16K)

CS4398 - pin --> resistor 1K --> - RCA (ground)

Any thought?

Thanx
You don't need resistors and you don't need to connect anything to - pin of the CS4398.

I have this DAC and tried it with OPA LME49720 and with transformators UTC A-20 connected between + and - of this DAC chip via 220R. I don't hear sufficient difference between sound with these OPAs and with transformator. I made A-B test for compariason. Sound of this DAC with LPF on LME49720 is good enough for me.
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Old 25th April 2012, 04:59 PM   #4
Ciorny is offline Ciorny  Austria
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OK thanks very much.

Has somebody compared with same DAC any high end transformer against a good cap at the exit concerning sound qualities?

I do not know yet what I should decide:

For instance: LL1690 costs a lot in contrast to good cap even from Mundorf:
Does it bring so much more "light" although technically seen a transformer introduce a some kind of "distortion"- still performs like filter - but maybe people love it?

On the other hand, a good capacitor alone may outperform any transformer..?
.
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Old 25th April 2012, 06:13 PM   #5
JensH is offline JensH  Denmark
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A passive analog out like the one you describe does not sound like a good idea to me.

I I have understood your description correctly, you will essentially end up with a single ended output from the + output. At least if there are other ground connections than the one from the RCA connector. I have used CS4398 (professionally) and found that the noise level is much higher if you use a single ended output, even when having a low pass filter on the output. You should either use a differential output going to a differential input or use a differential to single ended amplifier/filter, as described in the data sheet and evaluation board schematic.

A transformer can of course also be used to do the differential to single ended conversion, but personally I prefer op-amps.
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Old 25th April 2012, 06:43 PM   #6
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Quote:
Originally Posted by Ciorny View Post
OK thanks very much.

Has somebody compared with same DAC any high end transformer against a good cap at the exit concerning sound qualities?

I do not know yet what I should decide:

For instance: LL1690 costs a lot in contrast to good cap even from Mundorf:
Does it bring so much more "light" although technically seen a transformer introduce a some kind of "distortion"- still performs like filter - but maybe people love it?

On the other hand, a good capacitor alone may outperform any transformer..?
.
As I mentioned above I used UTC A-20 which is considered as one of the best transformers for this function and comparable with the LL1690. But I compared it vs excellent OPA. I can do A-B test vs Mundorf capacitor during this weekend. I will report the result.
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Old 25th April 2012, 10:33 PM   #7
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I have a DAC with the same chip and LM4562 as filters - straight out with no capacitors. I found that the noise below 20Hz is increased as opposed to the capacitor option. But if your next stage has capacitors, then you can go without them.
Sound with quality OpAmps is as good as it can get because the cip has voltage output therefore already has an OpAmp inside (for the I/V conversion).
Transformer "trick" is used on DAC's with curent output as I/V stage (personally I don't think is a good ideea anyway).
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Old 26th April 2012, 05:33 AM   #8
Ciorny is offline Ciorny  Austria
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Quote:
Originally Posted by JensH View Post
A passive analog out like the one you describe does not sound like a good idea to me.

I I have understood your description correctly, you will essentially end up with a single ended output from the + output. At least if there are other ground connections than the one from the RCA connector. I have used CS4398 (professionally) and found that the noise level is much higher if you use a single ended output, even when having a low pass filter on the output. You should either use a differential output going to a differential input or use a differential to single ended amplifier/filter, as described in the data sheet and evaluation board schematic.

A transformer can of course also be used to do the differential to single ended conversion, but personally I prefer op-amps.
I see, so you mean the SNR will rise if not used the differential output however: it does not only eliminate the DC-offset of the CS4398 (if done by op-amp or transformer correctly), but also any other "noises".

As far as I know, the CS4398 has no internal I/V converter due to direct voltage aggregation: please correct me if Im wrong.

However, a confrontation (A/B/C test) between

Op-amp / Transformer / Cap

concerning sound qualities would be quite interesting in spite of possible technical/measurable improvements or deterioration's.
Of course it depends of the quality of the used components, but the first tip would be quite interesting.
Please let me know, if somebody have the possibility or already done.
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Old 26th April 2012, 09:20 AM   #9
JensH is offline JensH  Denmark
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Maybe I didn't explain it clearly enough. I hope the following explanation will make it clear. In the following I will refer to the evaluation board description from Cirrus Logic, the CDB4398.pdf.

If you want a single ended output I would suggest to use the circuit around U1-A (and U18-A).

If you want a differential output the circuit around U5 and U10 (and U13 and U16) works well. But don't use this circuit to provide a single ended output.
Other op-amps can of course be used, e.g. the LM4562.

I have used both circuits and they work well. But taking a single ended output from e.g. U5 is not a good idea. The noise level is much higher than if you use the circuit around U1-A.
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Old 26th April 2012, 09:48 AM   #10
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Quote:
Originally Posted by SoNic_real_one View Post
Transformer "trick" is used on DAC's with curent output as I/V stage (personally I don't think is a good ideea anyway).
I absolutely agree with this statement. I have tried 2 types of transformers cheap but good Monacor LTR-110 and expensive UTC A-20 just because many people on this forum recommended to use transformers instead of LPF on OPAs. Conclusion of this test is following: either it doesn't sound better with transformers or my ears not good enough to hear the difference. I believe that my tube 300B SET amplifier and B&W speakers are not too bad and would allow to hear difference with good ears.

@Ciorny. We live in the same city. If you want I can borrow you for a while Monacor LTR-110 transformers that you can play with it and make your own decision.
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