GUSTARD DAC-R26 Balanced Decoder R2R+1Bit Dual Native Decoding Music Bridge

[camrector]

Thanks - that file is really good. I'll need to read it again to fully take it all in.

The one thing it doesn't really answer though is the Gustards 1bit architecture and the R2R ladder. None of the diagrams have that example in line with the Gustard's architecture, where the Gustard uses it's 1 bit DAC and then uses the R2R ladder to do the final d/a work..

It seems a bit of a contradiction really. I would of thought the 1 bit DAC would of done the full conversion, without the need for the R2R ladder? That's why I'd love to know more about the technical details behind why the Gustard manual says with 'DSD Direct on', the file still goes through the R2R ladder. I always thought the ladder was for PCM conversion and wasn't needed for DSD direct?

My knowledge here is not great so would love to know more.

I think that maybe the manual meant to say “resistors” instead of “ladder”
Unless The DSD DAC also uses the resistors of the ladder.
In this photo I believe we have a combo of B and D. That “optimization for analog filter” the R26 I believe is calling an interpolation fir filter.
This linked article has good info on why these types of filters are needed to reduce DSD noise.
http://s-audio.systems/dsd-filter/?lang=en

 

[labeelen]

Thanks - that file is really good. I'll need to read it again to fully take it all in.

The one thing it doesn't really answer though is the Gustards 1bit architecture and the R2R ladder. None of the diagrams have that example in line with the Gustard's architecture, where the Gustard uses it's 1 bit DAC and then uses the R2R ladder to do the final d/a work..

It seems a bit of a contradiction really. I would of thought the 1 bit DAC would of done the full conversion, without the need for the R2R ladder? That's why I'd love to know more about the technical details behind why the Gustard manual says with 'DSD Direct on', the file still goes through the R2R ladder. I always thought the ladder was for PCM conversion and wasn't needed for DSD direct?

My knowledge here is not great so would love to know more.

I share your doubt about use of the ladder in Direct DSD decoding.

Wouldn’t be surprised if there is a copy/paste error in the R26 manual as the texts for ‘pcm nos’ and ‘Direct DSD’ are identical:
“Default is OFF. Turn on to bypassing the internal interpolating FIR filter. The raw DSD stream is sent into the R-2R ladder directly.”

 

[labeelen]

I think that maybe the manual meant to say “resistors” instead of “ladder”
Unless The DSD DAC also uses the resistors of the ladder.
In this photo I believe we have a combo of B and D. That “optimization for analog filter” the R26 I believe is calling an interpolation fir filter.
This linked article has good info on why these types of filters are needed to reduce DSD noise.
http://s-audio.systems/dsd-filter/?lang=en

I think you are right, DSD Direct is handled by this section of the pcb:

https://wxalbum-10001658.image.myqc...7639.jpg?imageView2/2/w/1100/q/75/format/webp

 

[Odezra]

I think you are right, DSD Direct is handled by this section of the pcb:

https://wxalbum-10001658.image.myqc...7639.jpg?imageView2/2/w/1100/q/75/format/webp

Yea - If i read this - I think the file goes through the 1 bit multidac and straight into the output stage? Turning on Direct DSD effectively turns off the interpolation filter so that the signal is simply upsampled by Roon / HQ player before hitting the 1 bit multidac (with no filter applied) and then into the output stage? In this case - the ladder is not used right?

If i am right - wouldn't this correlate to model D on cam's diagram? (i.e. no ladder in play?)

I think that maybe the manual meant to say “resistors” instead of “ladder”
Unless The DSD DAC also uses the resistors of the ladder.
In this photo I believe we have a combo of B and D. That “optimization for analog filter” the R26 I believe is calling an interpolation fir filter.
This linked article has good info on why these types of filters are needed to reduce DSD noise.
http://s-audio.systems/dsd-filter/?lang=en

EDIT - I am trying to work out whether I am using the ladder or not. My latest listening has been DSD direct. Am trying to understand whether after all this A/B testing, I am preferring the 'R2R sound' as implemented by Gustard, or whether i have ended back in Delta-Sigma land. Would be good to know - well help me on my journey. Would also have me do some more A/Bing with the ladder to see what's going on. My read of the above is i am currently not using the R2R ladder.

 

[camrector]

I think you are right, DSD Direct is handled by this section of the pcb:

https://wxalbum-10001658.image.myqc...7639.jpg?imageView2/2/w/1100/q/75/format/webp

You can use the R2R ladder or a part of the ladder for DSD. So I’m thinking that that is what they are doing.
DSD Direct “on” is just bypassing the oversampling filter.

This article explains how an R2R ladder does that.
https://forum.psaudio.com/t/do-most-dsd-dacs-convert-dsd-to-pcm/23791?page=2

 

[Jake2]

I think that maybe the manual meant to say “resistors” instead of “ladder”
Unless The DSD DAC also uses the resistors of the ladder.
In this photo I believe we have a combo of B and D. That “optimization for analog filter” the R26 I believe is calling an interpolation fir filter.
This linked article has good info on why these types of filters are needed to reduce DSD noise.
http://s-audio.systems/dsd-filter/?lang=en

Some quality challenge and research there Dude, will digest later, and for what it is with pretty sure Jussi, the HQP creator, doesn’t yet have an R26 in hand to assess in the real.

 

[Odezra]

Some quality challenge and research there Dude, will digest later, and for what it is with pretty sure Jussi, the HQP creator, doesn’t yet have an R26 in hand to assess in the real.

Yea it's really good.

And just to throw another interesting tidbit into the works.

L7AudioLab had this to say about the measurements of DSD direct, which i don't fully understand. it seems to indicate less sinad.

Again - putting this out there for interest. Trying to optimise the performance of the gustard, and open to more trialling of it's different settings.

 

[camrector]

Yea - If i read this - I think the file goes through the 1 bit multidac and straight into the output stage? Turning on Direct DSD effectively turns off the interpolation filter so that the signal is simply upsampled by Roon / HQ player before hitting the 1 bit multidac (with no filter applied) and then into the output stage? In this case - the ladder is not used right?

If i am right - wouldn't this correlate to model D on cam's diagram? (i.e. no ladder in play?)

EDIT - I am trying to work out whether I am using the ladder or not. My latest listening has been DSD direct. Am trying to understand whether after all this A/B testing, I am preferring the 'R2R sound' as implemented by Gustard, or whether i have ended back in Delta-Sigma land. Would be good to know - well help me on my journey. Would also have me do some more A/Bing with the ladder to see what's going on.

We are most likely still using the ladder but just a few of the resistors that are on it.

 

[camrector]

Yea it's really good.

And just to throw another interesting tidbit into the works.

L7AudioLab had this to say about the measurements of DSD direct, which i don't fully understand. it seems to indicate less sinad.

Again - putting this out there for interest. Trying to optimise the performance of the gustard, and open to more trialling of it's different settings.

Those measurements are confirming exactly what I was theorizing about quantization noise. The first picture he says has DSD direct on.
The SINAD is 68db.
In the second one he says it’s better to have it off and the SINAD jumps way up to 91db. The higher number the better with SINAD.
So bypassing that filter is causing more noise with DSD.

 

[Nada]

So bypassing that filter is causing more noise with DSD.

What filter?

 

[camrector]

What filter?

The internal interpolation fir filter.
Turning DSD direct to “on” bypasses that filter.

 

[Nada]

The internal interpolation fir filter.

Thanks. Can a FIR work on DSD directly? I thought a FIR needs multibit ie PCM to process?

So it looks like for R26 to play DSD without loads of noise, it turns it back to PCM (back as most DSD was originally recorded and mastered in PCM) and then uses the R2R ladder.

Why bother with DSD at all?

 

[BShaw]

Well this place sure has been cookin' today, must be Saturday
I'm chiming in here because I recently posted about my OCK-1 and issues with the R26 reading "ext err". I've discovered when I leave the clock on for 20-30 minutes, the error disappears, and all is well in musicville. And well it is - with the Beatechnik cable in place, (warning: subjective outburst ahead, may not be suitable for the anointed defenders of science) HOLY SCHMIDT. the music just has so much 'in the pocket' groove, the soundstage is beyond big with the R26, it's absolutely immersive! Piano is one of the hardest things to get right IMO, and piano sounded just right tonight. I was enjoying the music like never before, just blown away by the quality of sound. Wow.

I wonder - does anyone here keep the OCK on all the time?

 

[Odezra]

Thanks. Can a FIR work on DSD directly? I thought a FIR needs multibit ie PCM to process?

So it looks like for R26 to play DSD without loads of noise, it turns it back to PCM (back as most DSD was originally recorded and mastered in PCM) and then uses the R2R ladder.

Why bother with DSD at all?

I am not sure that’s quite correct based on the articles cam has posted.

The FIR works pre dac stage.

I have just a/b’d dsd direct on / off with up sampled dsd files from Roon. There is a v small difference. Comes across as a half db increase in gain going from off to on. We are not talking major changes. I am guessing the FIR on attenuates the signal per cams articles.

It’s hard to tell what’s better so far. The science says that dsd off will have larger sinad and should be better. The perceived change in gain muddles up the testing for me - I can blind test and pick dsd on every time. But am not sure I can tell which is better.

Will test some more but on my system - not sure there’s much to worry about either way.

 

[Odezra]

Well this place sure has been cookin' today, must be Saturday
I'm chiming in here because I recently posted about my OCK-1 and issues with the R26 reading "ext err". I've discovered when I leave the clock on for 20-30 minutes, the error disappears, and all is well in musicville. And well it is - with the Beatechnik cable in place, (warning: subjective outburst ahead, may not be suitable for the anointed defenders of science) HOLY SCHMIDT. the music just has so much 'in the pocket' groove, the soundstage is beyond big with the R26, it's absolutely immersive! Piano is one of the hardest things to get right IMO, and piano sounded just right tonight. I was enjoying the music like never before, just blown away by the quality of sound. Wow.

I wonder - does anyone here keep the OCK on all the time?

Mines been on the whole time since purchase (nearly a month). Not sure what the story is here - whether it should be powered off at the end of each session.

BTW - ‘EXT ERR’ means external clock is not syncing with Gustard so it going away after 30 mins makes sense.