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Old 22nd November 2012, 10:10 PM   #1
dddac is offline dddac  Germany
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Default A NOS 192/24 DAC with the PCM1794 (and WaveIO USB input)

It has been a Long time after the DDDAC1543 saw the light and the world moved on, especially if we look at available sound track material. So much great soundtracks with high Resolution. Red book is not dead of course, but if I spend money on sound tracks, I look for 96/24 or even better 192/24, or the SACD equivalents 88.2 and 176.4...

In the past year I have been working on my new project: designing a DAC which will play up to 192kHz / 24bit material from a PC (or Mac...) There are many DACs who can do this, but I wanted to design a NOS version, as so far, every listening test I did, this led to a more open, natural and detailed sound.

I found this to be possible by using the well-known PCM1794 and avoiding the digital filtering built into the chip. This proved to be quite tricky, but I managed to find the key to do it. It has been a great adventure with much to learn and a fantastic result at the end....

To feed the DAC, I kind of integrated the WaveIO USB Receiver from Lucian. Great design and better sounding than all others I tried (see my website for this as well); I give a very detailed report on www.dddac.com

You can download the circuits here: dddac1794_nos_ver30.pdf



The Images below show:
The Mainboard with I/O and I2S to right justified conversion
The actual dual mono DAC Module (can be stacked parallel)
Built up with 4 modules and two power supplies (5 and 12 Volt)
Wired up in Chassis (Mundorf Gold silver oil output and optional Sowter 1:2
The DAC in my Audio rack
Another view inside
Block diagram


I opened this thread to share my design and experience and give a platform for questions, feedback, remarks and/or discussion...
Attached Images
File Type: jpg dddac1794nos1.jpg (152.7 KB, 6404 views)
File Type: jpg dddac1794nos2.jpg (200.9 KB, 6113 views)
File Type: jpg dddac1794nos3.jpg (206.0 KB, 5909 views)
File Type: jpg dddac1794nos4.jpg (223.1 KB, 5703 views)
File Type: jpg dddac1794nos5.jpg (235.5 KB, 5487 views)
File Type: jpg dddac1794nos6.jpg (440.4 KB, 1835 views)
File Type: png circuits_blockdiagram_large.png (111.4 KB, 2009 views)
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Old 22nd November 2012, 10:27 PM   #2
tuyen is offline tuyen  Australia
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Hi Doede,

The recently added 'Test Results and Specs' page is refreshing to know. Happily been enjoying my single board unit at the moment. I think I prefer the cap output over the o'netics dac buffer tx. Currently powering the mainboard/dac board with 12v from a lab power supply. The usb module running from 5V of usb cable.

Been listening to a few high-resolution (24/96) releases from the ACT label. Can really appreciate the step up in fidelity that your new DAC provides over your previous 16/44 DDDAC1543.

Looking forward to the PS Kit when it is ready. May be tempted to order a few more DAC boards while I am at it

Anyways, thank you again for your work on this new design and on development of the kit. I think it really suits beginner hobbyists like myself as the webpage is relatively easy to understand and build. Has certainly sharpened my soldering skills!
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Old 22nd November 2012, 10:32 PM   #3
dddac is offline dddac  Germany
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Quote:
Originally Posted by tuyen View Post
Hi Doede,

Currently powering the mainboard/dac board with 12v from a lab power supply. The usb module running from 5V of usb cable.

Anyways, thank you again for your work on this new design and on development of the kit. I think it really suits beginner hobbyists like myself as the webpage is relatively easy to understand and build. Has certainly sharpened my soldering skills!
Hi Tuyen,

Thanks for Feedback! The step up from using a separated 5Volt power supply in stead of bus power is significant. The power supplies are coming just a little patience
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Old 24th November 2012, 01:59 PM   #4
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Doede, what made you choose this chip over- say pcm1704 ?
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Old 24th November 2012, 07:53 PM   #5
ppap64 is offline ppap64  Canada
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Hi Doede
As an owner of a DDDAC1543 (2 tower) I have to say I've been extremely happy with its performance, to the point where Hi-res isn't a concern.
However, any potential improvement is intriguing, so I'm curious if Lucians' WaveIO can also be used with the DDDAC 1543 or is there an issue with how it would interact with the tower stacks.

Best regards
Peter
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Old 24th November 2012, 11:50 PM   #6
clivem is offline clivem  United Kingdom
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Originally Posted by studiostevus View Post
Doede, what made you choose this chip over- say pcm1704 ?
I also wondered why someone with a track record on R2R DAC designs would choose a delta sigma chip. The PCM1704 seems like an obvious choice for a NOS 192k/24 bit design, especially when you consider that the 1794 requires manipulation of I2S input to run NOS mode anyway, which would kind of negate any argument about a 1704 design requiring additional supporting circuitry.

If you factor in the design requirement for passive I/V, the 1794 has the current swing to do that, the 1704 doesn't. Maybe that's the reason. Will be interesting to hear what Deode has to say.
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Old 25th November 2012, 07:49 AM   #7
dddac is offline dddac  Germany
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Quote:
Originally Posted by studiostevus View Post
Doede, what made you choose this chip over- say pcm1704 ?
Few things:
general performance as DAC (which I considered as excelent)
192kHz possible
(high) current outputs (so I could parallel and do passive I/V)
the Option to avoid the digital filter
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Old 25th November 2012, 08:29 AM   #8
dddac is offline dddac  Germany
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Quote:
Originally Posted by ppap64 View Post
Hi Doede
As an owner of a DDDAC1543 (2 tower) I have to say I've been extremely happy with its performance, to the point where Hi-res isn't a concern.
However, any potential improvement is intriguing, so I'm curious if Lucians' WaveIO can also be used with the DDDAC 1543 or is there an issue with how it would interact with the tower stacks.

Best regards
Peter
Hi Peter,

Indeed, the good old DDDAC1543 still plays at top of the range.
The new DAC does show improvement on 44.1/16, but the real gain of course is with HD material (read the sound check 1 on my Website...)

yes, no problem. The WaveIO is a general board with I2S Output and it works perfect with the DDDAC1543...
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Old 25th November 2012, 08:34 AM   #9
dddac is offline dddac  Germany
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Originally Posted by clivem View Post
I also wondered why someone with a track record on R2R DAC designs would choose a delta sigma chip. The PCM1704 seems like an obvious choice for a NOS 192k/24 bit design, especially when you consider that the 1794 requires manipulation of I2S input to run NOS mode anyway, which would kind of negate any argument about a 1704 design requiring additional supporting circuitry.

If you factor in the design requirement for passive I/V, the 1794 has the current swing to do that, the 1704 doesn't. Maybe that's the reason. Will be interesting to hear what Doede has to say.
the current swing is one... and I did consider the PCM1704, but it only does 96kHz.... that's why i dropped it at the end
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Old 25th November 2012, 09:58 AM   #10
clivem is offline clivem  United Kingdom
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Originally Posted by dddac View Post
and I did consider the PCM1704, but it only does 96kHz.... that's why i dropped it at the end
Yes, but that's 96k at 8x OS. ie. 768kHz.
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