A NOS 192/24 DAC with the PCM1794 (and WaveIO USB input) - Page 33 - diyAudio
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Old 2nd May 2013, 09:48 AM   #321
bravi is offline bravi  New Zealand
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Default Additional boards

Hi Doede,

Any progress in your trial with 8 boards?

Looking forward to your experience on this.

Cheers!

Ravi
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Old 2nd May 2013, 10:00 AM   #322
dddac is offline dddac  Germany
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Quote:
Originally Posted by bravi View Post
Hi Doede,

Any progress in your trial with 8 boards?

Looking forward to your experience on this.

Cheers!

Ravi
Hey good Timing,

watch this Picture Made by my friend Dick. (as I had no time (again)

He just built it and it did not work at first... Digital noise. meaning the I2S signals were loaded too much. The solution was very simple. Change the 3,3 Volt Regulator on the Mainboard for a 5 Volt Regulator. All Chips (The Isolator on the WaveIO, the VHC164 Registers and the PCN1704 are all 5 Volt compliant. This Little Change made it work seamlesley !

Too early to give a commentary on the Sound quality. But that will follow for sure...

PS. I also uploaded a nice example of a solo DAC in a nice Chassis solution !
Attached Images
File Type: jpg DDDAC 1794 Octopus achterkant.jpg (372.4 KB, 704 views)
File Type: jpg DDDAC 1794 in audiorek.jpg (198.2 KB, 600 views)
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Old 2nd May 2013, 02:17 PM   #323
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Originally Posted by dddac View Post
by the way, this article is theoretically correct, but they leave the most important part away, the DC bias of the dac output.... the idea of this document works only, when the dac output is designed to work at zero volt DC output and swing around this point....
Hi Deode,

The DC bias is the reason to connect the center tap to common. This is the answer I got from a Chinese HiFi forum, the guy who gave me the answer used a transformer directly to the POS and NEG of 1794, and connected the center tap to common. And he used 1pc 1794 chip for one channel as well, and summed the output up exactly the same as your circuit. Your answer and his answer are just on the 2 side of this case and against each other, that made me a bit confused.
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Old 2nd May 2013, 03:25 PM   #324
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Hi Deode

Sorry for the previous post as you already answered the question. Actually the case I read from the Chinese forum was: the DC resistance for his transformer is around 120Ohms, so he just took all the resistor away, and used the transformer directly.

For this transformer: EDCOR - XS4400, the DC resistance of each winding is 116Ohms, I guess the winding can be used directly as a resistor.
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Old 3rd May 2013, 06:14 AM   #325
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Default Balanced outputs

I have a question about balanced output options which I would be grateful for advice on.

I have a DDDAC with single DAC board and standard output caps to RCA output. My preamp is an Ayre K-5xemp which apparently sounds best in all balanced operation. Before fitting balanced sockets to the DDDAC I want to be sure I'm on the right path.

The DDDAC has an output of 1.2v. The Ayre accepts a max input of 8v (bal) but I cannot find a figure for input sensitivity through single or balanced inputs. The input impedance is stated as 20k ohm single, 40k ohm balanced (20k ohm per phase).

So my questions/ concerns are:
1. How can I be sure that the 1.2v output will be sufficient for the Ayre's balanced input?

2. Given the input impedance of the Ayre are there particular output caps I should consider as a good match and upgrade over the standards? (As alternatives to the Mungdorfs)

3. Is balanced output possible when using Sowter transformers? (which I believe output circa 5v)

Many thanks.
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Old 3rd May 2013, 06:51 AM   #326
dddac is offline dddac  Germany
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Quote:
Originally Posted by lxiaob View Post
Hi Deode

Sorry for the previous post as you already answered the question. Actually the case I read from the Chinese forum was: the DC resistance for his transformer is around 120Ohms, so he just took all the resistor away, and used the transformer directly.

For this transformer: EDCOR - XS4400, the DC resistance of each winding is 116Ohms, I guess the winding can be used directly as a resistor.
Hi,

it is Doede by the way

the idea of using the DC resistance as the Bias Point is not so bad. 116 Ohm is than for one module kind of right. But do not forget, at AC the DAC needs to see a solid load to avoid wrinkled Transfer characteristics and distortion. Meaning, you need to calculate the AC load seen at the Primary. This MUST be round 100 Ohms over a wide frequency range. so take care the secundary load is right. I would even place a resitosr between POS and NEG for this purpose and Keep high resistance secundary. Pick your choice.

The proof is in the eating. Can't tell how good the transformer is at low and high ferquencies of course. Just give it a try
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Old 3rd May 2013, 06:55 AM   #327
dddac is offline dddac  Germany
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Quote:
Originally Posted by crimsondonkey View Post
I have a question about balanced output options which I would be grateful for advice on.

I have a DDDAC with single DAC board and standard output caps to RCA output. My preamp is an Ayre K-5xemp which apparently sounds best in all balanced operation. Before fitting balanced sockets to the DDDAC I want to be sure I'm on the right path.

The DDDAC has an output of 1.2v. The Ayre accepts a max input of 8v (bal) but I cannot find a figure for input sensitivity through single or balanced inputs. The input impedance is stated as 20k ohm single, 40k ohm balanced (20k ohm per phase).

So my questions/ concerns are:
1. How can I be sure that the 1.2v output will be sufficient for the Ayre's balanced input?

2. Given the input impedance of the Ayre are there particular output caps I should consider as a good match and upgrade over the standards? (As alternatives to the Mungdorfs)

3. Is balanced output possible when using Sowter transformers? (which I believe output circa 5v)

Many thanks.
No problem let me see if can answer this:

1. Use your ears and neighbors… if it plays loud enough it is ok By the way, balanced out is 2,4Volt
2. The brand is 100% personal choice…. For 20k 2,2uF is sufficient …
3. With the old ones not (there was no center tap) that has changed, new orders have a center tap, so YES, it can be used as balanced


Hope this helped!
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Old 7th May 2013, 08:25 AM   #328
tuyen is offline tuyen  Australia
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So can we confirm that a single 12v power supply kit can power 8 modules??

Curious to hear Dick's thoughts between 4 and 8 modules.
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Old 7th May 2013, 02:44 PM   #329
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Originally Posted by tuyen View Post
So can we confirm that a single 12v power supply kit can power 8 modules??

Curious to hear Dick's thoughts between 4 and 8 modules.
I suppose Doede's 12v supply will do (just).

I hope 8 boards will not be better than 4, it will drain my wallet building another 4 units with shunt supplies and a Salas supply cannot take the extra current.
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Old 7th May 2013, 03:42 PM   #330
xslavic is offline xslavic  Moldova
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Why dont you use simple regulators,you can filter it and its very efficient-youll get your 129 db snr
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