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The DSC1 DAC as a way to understand how a simple DSD DAC actually works


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By the way, so as not to confuse folks, the references to no schematics were to the Chinese boards - @Miska has schematics and a bill of materials on the Signalyst site.  (@jabbr , I'm sure you have schematics for your version at DIYAudio.  BOM as well?)

One never knows, do one? - Fats Waller

The fairest thing we can experience is the mysterious. It is the fundamental emotion which stands at the cradle of true art and true science. - Einstein

Computer, Audirvana -> optical Ethernet to Fitlet3 -> Fibbr Alpha Optical USB -> iFi NEO iDSD DAC -> Apollon Audio 1ET400A Mini (Purifi based) -> Vandersteen 3A Signature.

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1 hour ago, jabbr said:

 

Ok I thought perhaps they gave a bill of materials and schematic so you'd know what you were soldering where.

 

Balancing a single bit SDM stream is easy using a D-Flop which outputs + and -. Regarding digital switching noise, if both sides have very precise phase, then theoretically the switching signals will cancel. Changes in current will balance eachother. One issue, however, is when the signals arrive at different times to the chips. This can be caused by unequal trace path lengths and impedances. PCB routing can be important in this situation.

 

Does this make a difference? Well we talk about so-called "femtosecond" clocks. Signals travel down a one foot PCB trace in 1 - 2 nanoseconds -- so if the trace lengths are unequal that's a lot of femtoseconds ;) Vias also insert uncertainty. Another issue is clock distribution -- when a trace is fanned out this causes reflections (and phase error). A clock distribution chip reduces that (along with trace termination).

 

I've thought it amusing that many folks get caught up with using the latest and greatest "femtosecond" or "atomic" clock without a care in the world about how the DAC circuit actually works... now I'd be fairly certain that vendors such as ESS (and any large chip manufacturer) spend a fair amount of resources modeling trace delay and fan-out etc. -- particularly when they work at 100Mhz. For Ghz applications its absolutely essential.

 

Anyways when I think about folks "upgrading" a cheap circuit with an unknown design by using the worlds greatest and most accurate clock -- which costs waay more than the circuit its being applied to, my brain goes into a fog...

I do my best not to think much about what others do. :)

 

And of course you are correct about the clocking - and the D Flop. That can readily be done on the original board as well, and by using a pair of boards stacked or sandwiched you have stereo. I realize it is sub optimal, but I haven't your expertise and muddle along the DIY trail the best I can with the limited resources available here...

Forrest:

Win10 i9 9900KS/GTX1060 HQPlayer4>Win10 NAA

DSD>Pavel's DSC2.6>Bent Audio TAP>

Parasound JC1>"Naked" Quad ESL63/Tannoy PS350B subs<100Hz

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3 hours ago, Jud said:

By the way, so as not to confuse folks, the references to no schematics were to the Chinese boards - @Miska has schematics and a bill of materials on the Signalyst site.  (@jabbr , I'm sure you have schematics for your version at DIYAudio.  BOM as well?)

Everything is on the DIYAudio site ... the desire to use even more discrete implementations means moving more to SMD components -- the through the hole jFets are an increasingly rare ... and expensive ... breed. SMD components are super cheap in contrast, though soldering them requires skill and is aided by equipment like a stereomicroscope. So maybe not for everyone though several people are working on it. That said, SMD is great for production -- there is typically a substantial setup fee needed to load the rolls of the specific parts but then the production is automated with pick-and-place and then wave solder -- like pizza :) 

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39 minutes ago, jabbr said:

Everything is on the DIYAudio site ... the desire to use even more discrete implementations means moving more to SMD components -- the through the hole jFets are an increasingly rare ... and expensive ... breed. SMD components are super cheap in contrast, though soldering them requires skill and is aided by equipment like a stereomicroscope. So maybe not for everyone though several people are working on it. That said, SMD is great for production -- there is typically a substantial setup fee needed to load the rolls of the specific parts but then the production is automated with pick-and-place and then wave solder -- like pizza :) 

 

In other words, if enough people were interested, there might be benefit to a group buy.  How many do you think would constitute "enough people"?  (Right now I unfortunately have to say that though I wish I could be part of it, I'm paying on a mortgage and a construction loan and a lot of the other stuff involved in building a new home and paying the bills on the current one.)

One never knows, do one? - Fats Waller

The fairest thing we can experience is the mysterious. It is the fundamental emotion which stands at the cradle of true art and true science. - Einstein

Computer, Audirvana -> optical Ethernet to Fitlet3 -> Fibbr Alpha Optical USB -> iFi NEO iDSD DAC -> Apollon Audio 1ET400A Mini (Purifi based) -> Vandersteen 3A Signature.

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4 hours ago, 4est said:

I do my best not to think much about what others do. :)

 

And of course you are correct about the clocking - and the D Flop. That can readily be done on the original board as well, and by using a pair of boards stacked or sandwiched you have stereo. I realize it is sub optimal, but I haven't your expertise and muddle along the DIY trail the best I can with the limited resources available here...

 

People are free to implement any suggested optimizations in any way they see fit. The prices for the Chinese boards are unbeatable and if they would simply publish their schematic I'd be all in favor... I'm not intending to criticize (don't know enough in any case), rather trying to discuss methods we can use to optimize the DSC1 design. That's why its an open design, so we can optimize and discuss the value of optimizations -- and at points where there are rough consensus, then folks might implement -- and at some point a wider board production could be considered. Its hard to know how much actual interest there would be.

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32 minutes ago, jabbr said:

 

People are free to implement any suggested optimizations in any way they see fit. The prices for the Chinese boards are unbeatable and if they would simply publish their schematic I'd be all in favor... I'm not intending to criticize (don't know enough in any case), rather trying to discuss methods we can use to optimize the DSC1 design. That's why its an open design, so we can optimize and discuss the value of optimizations -- and at points where there are rough consensus, then folks might implement -- and at some point a wider board production could be considered. Its hard to know how much actual interest there would be.

 

No offense taken...My point was that were are/few options. After waiting so long for Miska's I sprung for it. I be interested in a group buy, especially if it had separate I>V. I know you've been working on a jfet I>V. Although I would love to try whatever you/they concoct, I am pretty interested in using transformers for this application. This is a perfect situation for them,  and I have access to some very nice vintage iron.

 

How many boards do we need for a good run?

Forrest:

Win10 i9 9900KS/GTX1060 HQPlayer4>Win10 NAA

DSD>Pavel's DSC2.6>Bent Audio TAP>

Parasound JC1>"Naked" Quad ESL63/Tannoy PS350B subs<100Hz

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I have no idea of jabbr his boards, but to give an idea of what producing a 2-layer DDC1 board means financially, this might help. I ordered a run of 3 boards and paid about €45/piece for them. When you order 10, the prices already get sliced in half, ordering e.g. 20 means paying roughly one third of it. I am pretty sure it could be done less expensive elsewhere (e.g. Chinese) and I have no idea what the costs for the automated "pizza treatment" /pick and place and soldering automation are, but I'm pretty sure the costs are similarly less expensive when one adds higher volumes. To me in general the rule is that more than 10 boards ordered it gets financially viable.  However: the opamps and capacitors do add substantially to the costs, let alone the time needed if one solders everything by hand. SQ: IMHO it sounds really good, straight up, no fuzziness or softness, clarity and rhythm are really good. Very honest and life-like. To add, it has "weight" in all tones as well as being dynamically sound. I still do have some dsd artifacts, but these also might be because of a Amanero issue. (Anyone else having some noise modulation artifacts when playing very low level music BTW? )

 

And yes I am also curious Miska: could you shed some light on the possibility of  a 2nd version or could that take many more months/is that nowhere on your schedule anytime soon?

 

Hope this helps.

Screenshot_2017-06-03-00-34-29.jpg

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Just curious, what makes this the "perfect situation" for transformers? I 'd love to know the general schematic of the Lampizator. I'd guess a tube filter, but tube I-V?

 

In any case folks like @Superdad or @vortecjr are probably much much more expert than me at getting a good run of boards built ;) 

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1 hour ago, Marco said:

I have no idea of jabbr his boards, but to give an idea of what producing a 2-layer DDC1 board means financially, this might help.

jabbr has a number of variations of boards . Link to purchase at OSH park are on DIYAudio. They require minimum of three but one is needed for each channel, so you'd have one extra to mess up. There are separate boards for the digital section and the analogue section.

 

The digital boards are 4 layered with a proper ground and power plane. The only impediment to mass production is the use of Potato Semi logic for the d-flop and clock distribution. (I'm sure that could be worked out) .

 

The digital board uses standard design techniques.

 

The analogue board is mirrored & balanced (2 layered). It's circuits are less typical -- the I-V section (based on EUVL's SEN which itself is based in Pass' ZEN) is designed as very low noise with parallel (3) jfet & cascoded (total of 12 jfets). The design minimizes current noise. The  op amps are discrete Scott Wurcer hybrid jfet/bjt -- so entirely open design and an ode to the BJ862 :cool: -- it will have a unique sound hopefully a great one ☝️ 

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1 hour ago, shadowlight said:

I would be interested in purchasing the fully populated board if there was a group buy.  It would be even better if all the transformer and case was also available as part of the group buy :D

+1  :)

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10 hours ago, shadowlight said:

I would be interested in purchasing the fully populated board if there was a group buy.  It would be even better if all the transformer and case was also available as part of the group buy :D

 

Count me in on that one. 

"Science draws the wave, poetry fills it with water" Teixeira de Pascoaes

 

HQPlayer Desktop / Mac mini → Intona 7054 → RME ADI-2 DAC FS (DSD256)

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On 6/2/2017 at 7:01 PM, jabbr said:

Just curious, what makes this the "perfect situation" for transformers? I 'd love to know the general schematic of the Lampizator. I'd guess a tube filter, but tube I-V?

 

In any case folks like @Superdad or @vortecjr are probably much much more expert than me at getting a good run of boards built ;) 

Maybe "perfect opportunity" for transformers would be more accurate. Note, in either case I did not say "perfect solution".. I realize transformers aren't "cool" or en vogue, but they are a very elegant solution to this problem.

 

At dsd512 there is little noise near the audio band, and the transformers filter that while also providing a true balanced signal and galvanic isolation -all with one part. In contrast, I've seen some of your designs on DIYAudio - a dozen active devices, two power supplies and a dozen or two resisters/caps per channel. That is a lot of stuff. Transformers have limitations, but an active circuit would have to be very well tuned to compete sonically. I have no idea what the numbers look like.Of course one cannot just grab a xfmr out of a bin and expect it to sound great, but there is lots of great iron out there if you know what to look for, It makes all the difference and transformers are not cheap.. In my case, by using my transformer volume control as the filter, I get all of that with volume attenuation as a bonus. Lastly, my interconnects become part of the filtering too!

 

To wrap it simply, one could take a board such as this, add an LKS Amanero with Crystek "femto" clocks (also on eBay)and power it with a single 5 volt supply such as an UltraCap LPS-1.

Forrest:

Win10 i9 9900KS/GTX1060 HQPlayer4>Win10 NAA

DSD>Pavel's DSC2.6>Bent Audio TAP>

Parasound JC1>"Naked" Quad ESL63/Tannoy PS350B subs<100Hz

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Ah ok. The transformer is being used in lieu of the active output SK filter.

 

One of the reasons to separate the digital and analogue boards are to allow different analogue circuitry.

 

I had simply replaced the opamps in @Miska's original DSC1 design with discrete jFet versions -- in the case of the opamp serving as an I-V converter, with a discrete jfet I-V converter for the reason that we are dealing with current and the jfet has low current noise (which is itself diminished by using 3 parallel devices).

 

The opamps that form the SK filter have been replaced with a discrete hybrid jfet/bjt opamp design. There are other discrete designs, some that have less devices. That particular design was the primary work of Scott Wurcer (who designed opamps for AD) along with the input of some other luminaries and being itself a freely available DIYA design, I wanted to incorporate it into DSC1.2. To be very clear, there are other discrete designs that could be used, maintaining the same Sallen-Key filter characteristics that are used in the DSC1.

 

Now if the Chinese "DSC1" is transformer based, then the question arises: What makes it "DSC1" and what characteristics does it share with the Signalyst DSC1?

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2 hours ago, 4est said:

At dsd512 there is little noise near the audio band, and the transformers filter that while also providing a true balanced signal and galvanic isolation -all with one part. In contrast, I've seen some of your designs on DIYAudio - a dozen active devices, two power supplies and a dozen or two resisters/caps per channel. That is a lot of stuff. Transformers have limitations, but an active circuit would have to be very well tuned to compete sonically.

Let me expand on this -- and give a listening impression.

 

I have both a FirstWatt M2 which is transformer based as well as the J2 which is JFET based. Although the M2 is terrific, the J2 is phenomenal.

 

The original DSC1 sounds really excellent. I am looking for the J2 level of phenomenal.

 

The I-V section could be simpler, I could drop the cascodes, I could use 2SK209s instead of BF862s. There are 3 in parallel both to handle the needed current (with room to space) as well as to further reduce current noise.

 

The discrete op amp filters could clearly be simpler... maybe the next version will be ;) If I were as brilliant as Nelson Pass I could do this all with a single jFet so I'm only 1/36th as smart as he is ;) 

 

Power supplies: yep lots of independent floating power supplies. My goal outside of the DSC1 project is to develop a bullet proof isolation between the external world and the DSD signal going to those shift registers in the DAC. Lots of independent floating power supplies and I have a really cheap way to make them ;) (see DIYA dual bank floating power supply post) ... but that also means that any digital noise on the power lines to the digital board are isolated from the I-V section.

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15 hours ago, shadowlight said:

I would be interested in purchasing the fully populated board if there was a group buy.  It would be even better if all the transformer and case was also available as part of the group buy :D

And to others:

Are we talking about a group buy of the DSC1 designed by Miska, or about one of it's offspring?

ted_b   

  • ted_b
  • 7,749 posts

Has anyone given their listening feedback?

 

I'm thinking I'm not doing this copy and paste action very well, sorry for that.

 

Anyway, is it an interesting idea that we build several versions of this dsc1 and send it around so that anyone can make their mind up about which implementation they like best? I'd certainly be interested in hearing one with the jfets as well as the transformer version and/or the balanced one. I already have the original one, I'd have no problem whatsoever to send it away to someone. If he would send it to the next person within a few days, we'd all learn something as well as know what we want.

 

 

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1 hour ago, ted_b said:

Has anyone given their listening feedback?

Just to be clear: it's my copy and paste fiddling that makes it look as if ted_b is suggesting we should all listen to another ones DSC1. I wanted one post and quote 2 persons. Sorry for that ted_b!

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3 hours ago, jabbr said:

Let me expand on this -- and give a listening impression.

 

I have both a FirstWatt M2 which is transformer based as well as the J2 which is JFET based. Although the M2 is terrific, the J2 is phenomenal.

 

The original DSC1 sounds really excellent. I am looking for the J2 level of phenomenal.

 

The I-V section could be simpler, I could drop the cascodes, I could use 2SK209s instead of BF862s. There are 3 in parallel both to handle the needed current (with room to space) as well as to further reduce current noise.

 

The discrete op amp filters could clearly be simpler... maybe the next version will be ;) If I were as brilliant as Nelson Pass I could do this all with a single jFet so I'm only 1/36th as smart as he is ;) 

 

Power supplies: yep lots of independent floating power supplies. My goal outside of the DSC1 project is to develop a bullet proof isolation between the external world and the DSD signal going to those shift registers in the DAC. Lots of independent floating power supplies and I have a really cheap way to make them ;) (see DIYA dual bank floating power supply post) ... but that also means that any digital noise on the power lines to the digital board are isolated from the I-V section.

 

I do not think a comparison of M2 to this is reasonable, they are different parts and applications. The M2 is an autoformer used as a v-gain stage of an analog signal whereas the DSC1.dif is using a 1:1 line isolation transformer as a combined LPF, galvanic isolater , balancer  and in my case, an attenuation device. I am using a Bent Audio/Music First TVC (not AVC), but there are options. Here is a $400 DIY one: http://www.sacthailand.com/ 

 

And please do not think I mean this to disparage NP or yourself. He understood what he was doing   http://www.firstwatt.com/pdf/prod_m2_man.pdf    with the M2, and I assume you do as well.

Forrest:

Win10 i9 9900KS/GTX1060 HQPlayer4>Win10 NAA

DSD>Pavel's DSC2.6>Bent Audio TAP>

Parasound JC1>"Naked" Quad ESL63/Tannoy PS350B subs<100Hz

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28 minutes ago, 4est said:

And please do not think I mean this to disparage NP or yourself. He understood what he was doing   http://www.firstwatt.com/pdf/prod_m2_man.pdf    with the M2, and I assume you do as well.

Oh not at all -- I am using the M2 vs J2 simply as an analogy! and happy to discuss and defend my design issues. I think the digital board is fairly standard design wise -- assuming you want balanced, a ground & power plane with a bypass cap network, and a clock distribution network with similar propagation delays.

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  • 2 weeks later...

Audio Note use transformer for DAC.

http://www.ankaudiokits.com/agrovedac.html

 

The output of most resistor ladder DAC chips is in the form of a current rather than a voltage. There are many ways to convert the current into a voltage but the most commonly used system is that of an op-amp connected as an I to V converter. This system requires the use of a high degree of feedback, and as a result there are problems associated with it. One of those is internal slew rate limiting of the op-amp itself. The rate of change of current at the output of even an audio DAC is very fast indeed. Even modern fast op-amps will slew limit internally and that affects sound quality. Some engineers have found that using extremely fast op-amps improves the sound quality, but we have completely sidestepped the issue by using a transformer I/V system. The transformer not only provides an I to V function but the way it is used in our latest DACs transfers maximum energy from the DAC chip itself. This in itself reduces overshoot and ringing and because the system is slightly overdamped the rise time is reduced to an acceptable rate as well.

Even a carefully chosen resistor used as an I/V converter can be successful if executed properly but the transformer system is sonically superior for the reasons of energy transfer outlined above.

The output from the I/V is fed into an amplifying stage, of course using valves. This can be a simple single valve stage up to a specialized line driver as found in the M3 to M8 preamps.

 

 

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10 hours ago, Eclectico said:

I think there is something wrong to use only i/v transformer instead of analogic fir filter.

We loose the 42 db slope of the frequency. 

The square wave form should change with only an i/v tranformer...

There is missing something.

Audio note almost exclusively uses the AD1865 dac chip in their products. It's a 18 bit ladder dac. Afaik they don't use an "analog fir filter", so it might not be applicable to their products. Transformers are funny things: "Slightly over damped" means something like a slightly lower load than the 1700 ohm output impedance they state in the datasheet of the ad1865, and also keeping the energy transfer maximum seems to point at this. Many dacs they manufactured incorporated an enclosed filter as well as a transformer, with a ratio of 1:1 or 1:2. The filter used resistors to load the current output of the chip. In later years they completely abandoned filtering of the deliberate kind whatsoever, don't know what they do for the last 5 years or so. It's hard to manufacture a high bandwidth transformer at high impedance sources like a -sort of- current source. Though 1700 ohms arent that bad, the dsc1 has an output impedance of about 470 ohm, many times lower, and it would probably also be more uniform in its impedance. Ladder dacs tend to change output impedance depending on the output level, so distortion products are more erratic. Also, I'm not sure if capacitive coupling in the transformer is sufficiently mitigated to state the rf demons of dsd and ladder dacs are sufficiently filtered out without added filters behind one, after going through a transformer. I would love to see some wide bandwidth (normal and common mode, above e.g. 100KHz) measurements of the dac output to prove that is the case and/or capacitive input measurements of the transformers' input and coupling to the secondary windings.

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Marco,

 

About Audionote and the fact they don't use fir filter, I have search to understand reason.

I share what I find, IMO i think it 's logical: http://www.6moons.com/audioreviews2/metrum/2.html

 

In the case of HQ player treatment by computer, aim of fir filter is just to convert square wave in sine wave, we agree with that.

For 16 bits dac,  LSB= 1/65536 => we can see on the image attached that without filter, it's appear like a filter sine wave due to small LSB. In the 6moons reviews, it' s appear ear is like a filter.

So fir filter should not give better results in this case.

 

But with  DSC1 DAC , LSB=1/32 equivalent of 5 bits, fir filter appear to be more important..

If Miska can confirm.

 

In other points, what is the accuracy of the sine wave in the output of DSC1 dac in comparaison to 16 bits dac?

Output is 32 possible voltage levels against 65536 for 16 bits DAC...

What think about that?:(

 

L0108_BitGraph.png

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33 minutes ago, Eclectico said:

In other points, what is the accuracy of the sine wave in the output of DSC1 dac in comparaison to 16 bits dac?

Output is 32 possible voltage levels against 65536 for 16 bits DAC...

What think about that?:(

 

The DSC1 DAC has an analog filter which follows the shift registers and I-V. The analog filter results in an approaching infinite number of output voltage levels.

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