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Output transformers for DACs
Output transformers for DACs
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Old 4th October 2019, 09:01 AM   #211
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
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Join Date: Sep 2008
Location: Kazakhstan, Almaty
Output transformers for DACs
All I want to say is that the shielding pin if connected to the DAC chip' ground (to pin 11 of ES9038Q2M at least) - it helps to eliminate the noise (FFT proving it btw). All other cases including connection of "shielding can" to the chassis\enclosure\case - depends on the particular implementation and is out from schematic I shared above. It is up to the DIYer, who is building the DAC in particular case. Nobody prevent you to isolate these shieldings from the whole enclodure - just avoid the contact of "shielding can" with chasis - nothing extraordinary.
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Old 4th October 2019, 09:46 AM   #212
lemon is offline lemon  Greece
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Thanks for the info, bisesik
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Old 8th October 2019, 04:10 PM   #213
randytsuch is offline randytsuch
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Join Date: Jan 2003
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My setup is:
pi3b
ian's shield board (board with ground plane and pass through connectors)
ian's fifopi
ian's dual mono es9038 dac
bisesik transformer output board

I ordered ian's un-populated opamp output boards, but never built them up or tried them.

Still tweaking the digital part of the setup, but I have no urge to try another output stage, I'm really happy with my transformer based output.

Its easy to implement, you don't need to generate the +/- 12 or 15 or whatever for opamps.

IMHO, a bargain for what you get. I expect it would take a lot more work and/or money to get a better dac output stage.

Randy
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http://randytsuch-audio.blogspot.com/2005/10/my-system.html
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Old 9th October 2019, 05:35 AM   #214
lemon is offline lemon  Greece
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Hi bisesik,
At the post #8 you have upload FR diagram with 10K load.
It seems in the range of 20-20KHz the FR response is flat and there is no need any LPF at the secondary.
I don't know how will be the FR Response with 192KHz sampling file, the trafo rises the upper part of FR Response usually.

At the post #36 you said
Quote:
=There is more powerful LPF in case of ES (or AK) DACs - its inner Digital LPF. My aim is not to add additional LPF if possible.
But, we know that the AK series 449x had a choice of 50/150KHz LPF on DSD only, to PCM files it simples some filters (linear phase sharp roll-off, linear phase slow roll-off e.t.c)

If we wanna to apply a LPF on secondaries, which is the best solution (I have attached two schemas about it) for voltage output trafo (80H:80H, 1:1)?
Attached Images
File Type: png LPF1 secondary.png (49.6 KB, 260 views)
File Type: png LPF2 secondary.png (49.9 KB, 261 views)
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Old 9th October 2019, 03:10 PM   #215
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
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Join Date: Sep 2008
Location: Kazakhstan, Almaty
Output transformers for DACs
Hi lemon. Your questions are more for the particular DAC implementation at DIYer's side and I know cases when in the same setup one of my friends chosed to use Zobbel network at the secondary while the second guy concludes that he prefer without LPF. I remind - at the same time/setup. That is why I am a bit "confused" and understand that in your setup might be that sonically there will be no reason to use capacitors (or Zobbel) - I don't know. Technically the difference between cap only and Zobbel - the targeted shape of the LPF curve. Better to choose the desired by listening. Rasmussen methodic looks useful practically: -0.7dB at 10kHz and -2dB at 20kHz for example. This curve shape depends not only from the cap/res values, but from attached load impedance too. And it can be simply happend that within the available capacitor's type and its value (the higher value - the worse usually) will be better to use Zobbel (it has more flexible possiblity to change the curve than capacitor in parallel).

Last edited by bisesik; 9th October 2019 at 03:22 PM.
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Old 9th October 2019, 05:44 PM   #216
lemon is offline lemon  Greece
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Join Date: Apr 2009
Bisesik thanks for the info.

I have thinking to use a 4 position micro-switch, at the first the zobel will be bypass and to the others 3 an appropriate combination for 10K, 20K and 40K load impedance.
I am thinking a very small silvered mica (330-470pF) for capacitor.

By the way, is that available the pin out of 1:0.5+0.5 trafo? I think this is the best setup for a true balanced output, isn't?
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Old 10th October 2019, 02:06 AM   #217
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
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Join Date: Sep 2008
Location: Kazakhstan, Almaty
Output transformers for DACs
Of course it is possible, I have emailed to you.
Though it is intersesting question regarding true\pseudo balanced output, but it relates more to the DAC chip than to transformer. Can anybody identify clearly what the ES or AK DACs the outputs have? Are they true balanced or pseudo? What is the clear definition for true\pseudo balanced output? If you will take, say... PCM1794 then it is impossible to operate with - and + outputs without GND at all - is it the true BAL mode then? Then all other DACs like ES or AK are pseudobalanced? (their + and - outputs can be used separately from chip's gnd)..
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Old 11th October 2019, 04:47 AM   #218
lemon is offline lemon  Greece
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I believe that all AK44xx series is a true differential output.

On page 63 of 4490's datasheet, says:
"The analog outputs are full differential outputs and 2.8Vpp (typ, VREFHL/R - VREFLL/R =5V) centered around VDDR/2and VDDL/2voltages..."

On trafos, never used the gnd connection, only the positive and negative output without any issue.
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Old 11th October 2019, 05:03 AM   #219
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
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Join Date: Sep 2008
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Output transformers for DACs
OK, if you have no any issues with noise, I agree .

It is more interesting to figure out why some DACs can operate with the single coil and others can not works like PCM1794.
Seems the DC-offset in 1794 have different polarity for + and - (in respect to GND) compared to AK/ES serries where the DC-offset polarity the same for both outputs (+&-).
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Old 11th October 2019, 10:17 AM   #220
lemon is offline lemon  Greece
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Difficult, to have right answers about your questions....
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