A NOS 192/24 DAC with the PCM1794 (and WaveIO USB input)

[dddac]

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...

 

[tuyen]

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!

 

[dddac]

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

 

[studiostevus]

Doede, what made you choose this chip over- say pcm1704 ?

 

[ppap64]

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

 

[clivem]

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.

 

[dddac]

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

 

[dddac]

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...

 

[dddac]

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

 

[clivem]

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.

 

[studiostevus]

Yes, but that's 96k at 8x OS. ie. 768kHz.

Correct, it should do 192 in nos mode. I am contemplating on designing a pcm1704 dac, but i am not sure if it's worth it. I generally find there is limited hi-def material around...

 

[Jackal29a]

Wouldn't it even do DXD in NOS mode?

 

[clivem]

Correct, it should do 192 in nos mode. I am contemplating on designing a pcm1704 dac, but i am not sure if it's worth it. I generally find there is limited hi-def material around...

There are several 192k/24 bit NOS designs built around the PCM1704 out there. Although the data-sheet states a max of 96k @ 8x OS, I believe Kingwa (Audio-GD) is running 192k @ 8x OS from his DSP to the 1704, which would imply that the chip is actually capable of a 1.536MHz word clock.

I have a little 96/24 material. Based on my own experiences, I still prefer that material run through 16 and 18 bit R2R DAC's, even with the loss of resolution.

 

[dddac]

Yes, but that's 96k at 8x OS. ie. 768kHz.

Very valid Point. I simply overlooked that in the early days. High price and output arguments played a role as well of course, as well minus power supply. After that I hold on to the PCM1794. Might have had still oversampling specs in mind then. Anyway, 96kHz was not the only showstopper. Does not change a thing on the fact the PCM1794 in NOS is performing great

Nevertheless it is tempting to try a pair of 1704 though

 

[dddac]

Wouldn't it even do DXD in NOS mode?

DXD must be supported by the USB Receiver. The WaveIO does not Support that according to specs (max 192kHz)

You would expect that the DAC as such would support this, as the 8x oversampling is omitted, but I have not been able to test this...

I see the next experiments coming

 

[dddac]

I generally find there is limited hi-def material around...

well have a look at my 3TB drive than

I believe there is more than enough out there and of excellent quality.
But that is my personal opinion of course

 

[Jackal29a]

DXD must be supported by the USB Receiver. The WaveIO does not Support that according to specs (max 192kHz)

The WaveIO does not go over 192KHz but at 39€ the Amanero board does (PCM up to 384KHz and also DSD):

http://www.diyaudio.com/forums/vendors-bazaar/216474-usb-i2s-384khz-dsd-converter.html

 

[clivem]

Nevertheless it is tempting to try a pair of 1704 though

Deode,

I've been pondering. I'm biased, a fan of the PCM1704, but you really should try this. Having already designed your main-board outputting right aligned, 7 delay right channel, 39 delay left channel, which from memory, is exactly what is needed for a 1704 design, without any changes. So an optional 1704 daughter board using your stackable design would be really cool! Sure, it means also adding a negative supply for the DAC chips and it would mean having to use an active output stage...... I'd buy a complete kit plus an optional 1704 daughter board if it was available........

 

[dddac]

exactly my thoughts... mainboard is ready to go ;-) that is the advantage of modular work .... Of course I do see issues in the extra supply and stage, but hey, this is hobby and I was already thinking what to do next.... no promises though

 

[clivem]

Of course, the other issue is cost. Using 4x K grade chips for 2 channel +/- @ $75 each, is $300 per daughter-board. A little more expensive than a pair of 1794's.

BTW, I just ordered a complete 1794 kit from your web store. Will be interested to hear how it compares to my own NOS DIY DAC's. I'll probably use Salas shunt regs for the power supplies and although I'll give it a go with passive out, I'm more than likely to drop the I/V resistor value and hook up a tube output stage...... CCS'd 6C45, or triode connected EF810 or d3a. We'll see.