R-2R Ladder DACs (in production 2015)

I could be wrong but I do not think so.

 

Using Schiit as an example, I was under the impression (perhaps incorrect) that the Gungnir is a non-oversampling DAC.

The Cambridge DACMagic Plus is an example of an over-sampling DAC (everything gets oversampled to 192kHz)

 

NOS = non-oversampling
No "filter" (DSP) before conversion

R-2R is the means of PCM conversion to analog and it is one of the types of resistor ladders. Most PCM DACs are delta sigma.

Most R-2R DACs are NOS. The totaldac from the list, for example, has a "treble" filter which can be defeated.

DSP filtering is well beyond my depth, but there are those do not want any DSP at all and then there are those who prefer only one or more of types of DSP filtering, mostly for delta sigma DACs. The important thing for me, and perhaps for some others here, is generally appreciating that much R&D goes into filtering in any of the top delta sigma DACs (perhaps related to reducing pre/post ringing). It is important to understand that there are DACs with no DSP and that those are virtually always R-2R. One might find "NOS DAC" being used interchangeably with "R-2R", since the two typically go together.

Finally, I'd like to drive home the point that 99% of all DAC discussions revolve completely around the chip, which of course is nearly exclusively a DSD or delta sigma PCM chip. Hopefully, we can encourage others to recognize that the chip is really a small part of what creates the sound signature. Really, the filtering, complex power supply designs, clocking, and analog section are where it's at. And then, of course, there's the matter of R-2R versus delta sigma.

 

Just to make this more confusing, the Yggdrasil upsamples (oversamples?) everything to 384kHz. Google the Yggy's "burrito filter".

 

You are describing upsampling and not oversampling. I think. I'm just thinking of the "8x oversampling filter" that we've all seen. This seems different than upsampling. I'm not the expert, so someone else can elaborate.

 

Useful information here:

 

aqua La Scala MkII D/A Converter
- Made in Italy
- proprietary DFD (Direct From Decoder) digital decoding without digital filter
- Valve-Mosfet direct coupling analog stage in pure class-A (interesting hybrid, no op-amp)
- transformer-based passive I/V conversion
- all digital inputs handle up to 24/192 aside from their proprietary




There other technical details which distinguish these DACs from one another. I'm not the best at spotting significant details. Maybe we can get some feedback on this DAC.

 

We're discussing the La Scala and La Voce at this link:

http://www.computeraudiophile.com/f6-dac-digital-analog-conversion/aqua-la-scala-ii-review-25203/g

 

I wonder how many DACs deploy a tube / MOSFET hybrid analog section?

Is the La Scala hardware able to be upgraded? Looks sort of modular.

One thing I think we'll see is that there aren't any "empty boxes" in the R-2R list.

Oh, and this La Scala does have a matching physical disc transport. Another distinction.

 

The Yggdrasil is both an oversampling DAC and an R2R DAC.

As I understand it, the difference between it and other oversampling DAC's is that it uses a closed-form filter that preserves the original samples.

 

This is from Mike Moffat at Schiit (their DAC designer) on the Yggdrasil design. I have zero idea what this means technically, but it does say that it oversamples:

What are the technical design goals? Preserve all of the original samples of the source data. To oversample, insert time and frequency domain optimized samples between the original preserved samples. Convert the signal back to analog at full bit width with no delta sigma reduced bit width, no added noise to be partially filtered out later, or stupid meaningless bullschiit claimed bit specs

 

The Yggy is likely the most commonly known R-2R DAC, so we'll end up comparing and contrasting it with the others a good bit. I'd think. So with that said, the filter in the Burr-Brown PCM1704 chips used in the La Scala are bypassed. This is what makes it an NOS DAC. The Yggy might be using the AD5791 for the filter or perhaps there's another chip for that. For example, the DAC in my CD player uses a separate filter chip for PCM before it passes to the conversion (delta sigma) chips.

 

This is what the Schiit website says about the filter:

Digital Filter: proprietary Schiit bitperfect closed-form digital filter implemented on Analog Devices SHARC DSP processor

 

CH Precision C1 D/A Controller
Switzerland
-NOS or selection of DSP filters
-Fully module



This is a "cutting edge" unit, which can be translated in a few different ways.

 

Adding this one to the list:
Phasure NOS1

 

^It looks like they stole design from Sound Anchors...

 

The TI (formerly Burr-Brown) PCM1702 also appears to be still available.

It goes back a few years and you'd have found eight of them in the excellent Kenwood DP7090 from 1997. Still in production though it seems and you can still but it for projects though for general production I'd assume it's been superseded. The chip itself could potentially go up to 16x oversampling.

In terms of performance, the 7090 was excellent. A non-descript £400 machine turned in a very decent performance that was as good as the more than twice as much Linn Mimk that replaced it. Wish I'd kept it and I doubt I've seen five turn up on Ebay since I sold mine back in 2006. A great used buy.

 

Certainly an odd shape! Few more to consider before the 'P's', but that Phasure sure is interesting.

 

Computer Audio Design CAD 1543
UK
-NOS (the extreme end of this camp!)
-USB input only
-5 shunt regulated power supplies each fed from their own custom toroid
-Passive I/V Duelund cap and output transformers




This unit is aimed at those who don't like what is perceived as "digital sound". If DAC time alignment matters to some ears, then this is one to audition.

 

Interesting looking unit - thanks for the info.

 

Scott Berry of Computer Audio Design was kind enough to respond to a few of my basic questions about R-2R. He remains a proponent of no DSP at all, but if there were any filtering he is adamant that a computer is better suited to the task (prior to sending data to the DAC). [think Phasure!] I wanted to ask more about DoP (DSD over PCM) as he recommends it for the CAD 1543. Also, I wonder if this 2012 or so design isn't due for an overhaul.

A bit off-topic, but my number one hang-up by far with USB DACs is that I've got a bunch of great DSD stuck on physical SACD. It's 2015 for pete's sake. The move to a "digital transport" is going to happen for most of us and it sure would be nice if my SACDs could come along.

 

yes it would. Many SACDs here.

 

Well, you can always get CH Precision's D1 transport (in addition to their PCM1704-based C1 DAC)...

 

^problem solved.

 

I will say that now fully realizing the potential of this Aqua DAC, I am seriously considering getting a CD transport...