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 µ --> + RCA --> amplifier (16K)
CS4398 - pin --> resistor 1K --> - RCA (ground)
Any thought?
Thanx
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 µ --> + RCA --> amplifier (16K)
CS4398 - pin --> resistor 1K --> - RCA (ground)
Any thought?
Thanx
Attachments
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.
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..?
.
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..?
.
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 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.
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.
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).
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).
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.
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.
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.
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.
I cannot understand that. Why transformer will give more solid bass than OPA? With LME47920 I don't feel lack of bass and the bass is very controlled.
while its been awhile since I looked at this chip's datasheet - in general this class of
Vout DAC use "full differential" sw-C filter CMOS op amp output circuit internally, has the same virtual gnd input structure as I/V
so you are really looking at a CMOS output op amp with switched inputs, relying on full differential operation to reject the DAC internal digital substrate noise common mode Sw-C clock feedthru, possibly give some distortion cancellation
for best specs you really should use a differential receiver on the DAC analog output – further, for low distortion, you want the loads to equal, relatively high Z - transformers give very low Z load at low audio frequency
and while the sw-C filter reduces image frequencies over a few Nyquist bands there is still clock frequency feedthru on the output - so low pass filtering is still highly desirable to remove clock feedthru, any common mode digital noise not removed by the differential receiver’s (often poor) RF input CMRR - balanced RC to Agnd with smt NP0 (low inductance) caps in front of any external op amp circuit will reduce the sw-C clok frequency at your diff/SE/filter op amp's inputs
at mixed signal interfaces like this it may pay to use op amps with better reputations for RF/EMI rejection at their inputs
Vout DAC use "full differential" sw-C filter CMOS op amp output circuit internally, has the same virtual gnd input structure as I/V
so you are really looking at a CMOS output op amp with switched inputs, relying on full differential operation to reject the DAC internal digital substrate noise common mode Sw-C clock feedthru, possibly give some distortion cancellation
for best specs you really should use a differential receiver on the DAC analog output – further, for low distortion, you want the loads to equal, relatively high Z - transformers give very low Z load at low audio frequency
and while the sw-C filter reduces image frequencies over a few Nyquist bands there is still clock frequency feedthru on the output - so low pass filtering is still highly desirable to remove clock feedthru, any common mode digital noise not removed by the differential receiver’s (often poor) RF input CMRR - balanced RC to Agnd with smt NP0 (low inductance) caps in front of any external op amp circuit will reduce the sw-C clok frequency at your diff/SE/filter op amp's inputs
at mixed signal interfaces like this it may pay to use op amps with better reputations for RF/EMI rejection at their inputs
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I have already thought to me that a difference output may have its advantages.
But I will try following this weekend:
Switch the OP-amp´s into virtually class a mode:
About the value of the resistor I am still unnerved, because contrary opinions rule in several forums.
I have simulated my circuit (the input sin values are not approved yet) and have inserted 2K as a bias resistor: whether is this value the right one? Bias current: 6mA.
Please let me have your opinions.
Thanx
But I will try following this weekend:
Switch the OP-amp´s into virtually class a mode:
About the value of the resistor I am still unnerved, because contrary opinions rule in several forums.
I have simulated my circuit (the input sin values are not approved yet) and have inserted 2K as a bias resistor: whether is this value the right one? Bias current: 6mA.
Please let me have your opinions.
Thanx
Personally, I think that the distortion of the OpAmp is low enough as it is and it is not worth messing with biasing in class A. It reduces the feedback capacity of the OpAmp on one alternance and limits the speed response on that alternance. It might work well for headphone buffer/amp, but for other stages, that rely heavily on a high open-loop feedback value, is a sub-optimal solution.
Hoever, more about bias in class A: Biasing Op-Amps into Class A
Hoever, more about bias in class A: Biasing Op-Amps into Class A
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I tested this DAC not only with very good transformers but also with tube stages in class A (SRPP and with cathode follower using Telefunken 12AX7).
The best sound for my ears gives LPF of this board with LME49720 which has THD+N 0.00003 at 3V RMS. This OPA was designed for usage in active filters and it gives very good result. I like sound of this DAC.
The best sound for my ears gives LPF of this board with LME49720 which has THD+N 0.00003 at 3V RMS. This OPA was designed for usage in active filters and it gives very good result. I like sound of this DAC.
My statement didn't say trafo brings more bass than opamp...my statement just indicate the utc-20 give you the impression of better bass than without it (like the original output stage) base on my experience. There's might be a technical explanation but I'm not expert on these area.
If you feel LME47920 is good for you that stick to it perhaps you can improve areas like power regulator for instance for the next mods.
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