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

[Marco]

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.

[Marco]

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 

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   

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Posted 1 hour ago · 

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.

 

 

[Marco]

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!

[Marco]

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.

[Marco]

2 hours ago, 4est said:

 

I can confirm this as it confounded me for awhile thinking I had an issue with my server. Thanks for the heads up on that one awhile back Jussi! FWIW, I even had soft clicking in the background of quiet passages with DSD256.

The newer firmware versions also don`t work for me (on Windows OS). After lots of reflashing I settled for "CPLD_1080_XC12"and "firmware_1097c". Lots of hassle to get dsd512 working.

 

What version did you end up with?

[Marco]

On 2017-6-21 at 5:59 PM, Eclectico said:

I agree and I see the power of DAC in accordance to time steps (abscissa for sine wave).

But let's look a little more on the ordinate.

Shift register are supplied by 3.3V, resistors are 8.2Kohm, at the end of I/v converter, the maximum output voltage can reach 6.4V. And the minimum output voltage available is 0.2Volt.

 

If we take example with Mola Mola dac for the maximum output voltage of 6.4V, min output voltage could be 0.025V.

258 combinations available.

 

In comparison if the output voltage should be at 0.1 Volt, we cannot obtain this value with DAC DSC1=> we can obtain 0V or 0.2V.

 

I discussed with T+A, they have only 2 shift registers but coefficient change with different resistors values.

IMO 1.5% of accuracy seems a little to just.

 

 

 

 

Eclectico, DSD streams basically work by means of averaging the electrical values by a low pass filter.

In your example it could work by averaging a stream of 0,2 volt, next clock cycle 0,0 volt, next clock cycle 0,2 volt again, next 0,0 etc etc. On average this gives 0,1 volts.

As Jussi pointed out, the values are not changed every 22 microseconds as with PCM 44,1 KHz coding, but with DSD512 around every 42 nanoseconds/24 MHz. Averaging all these high data rate changes is easier done as well as less jitter sensitive when done with a FIR-filter. 

[Marco]

10 minutes ago, 4est said:

 

I am running 1096 and also running to the mute button! Ok, I stroll to the mute button as it takes a minute or two for playback to start while HQP is building the filter.

 

There is a very loud pop/crack at first turn on and also turn off/power down/sleep from my server. Beyond that there is only a tick when I start a playlist/album/track and additional tracks within those albums or playlists are fine.

Ah, the dreaded mute-problems. I am running the output of the shift registers at different speeds than the datastream from Amanero. I only get pops when turning the dac on and off and when shutting down the pc. For the rest no problems when starting, changing filters or starting/exiting HQPlayer. This is without a mute circuit populated. I think it works because the storage registers still get their clock independent of what amanero does, but I haven`t given it much thought yet.

The problems i had were different: fluttering/ noise related problems in one channel. It is amanero based, because with a different CPLD (CPLD 1080 channels swapped) the noise problems also swapped channels. Maybe it is my version of the board, but I have 2 and have the same problems with both at dsd512. 256 and lower worked fine.

 

You`re saying don`t have those problems at those speeds?

[Marco]

36 minutes ago, 4est said:

 

I had that fluttering issue in one channel using 1099. Upon switching back to 1096 (after much ado from ignorance), the fluttering went away. This is on an original Amanero, and the LKS Amanero type I am using now. The latter is not a copy per se, but slightly modded with extra regulators and I added a 22M Crystek clock from some previous experimentation.

4est, many thanks! I couldn't find this flutter related problem on the Internet,  so I reckoned it had something to do with my hardware. I'll see if 1096 works also.

Btw if you're interested in a, imho, better sounding source (and/or in a network connection), you might want to check out the Twisted Pears' Cronus/Rhea etc. No fluttering there whatsoever and easy to connect to the DSC1. I'm not sure if Mute is operational though..

[Marco]

7 hours ago, 4est said:

 

It had me too! I thought the same thing as well. I am using an older cpu and OCing it now for 512, but then I had assumed I just didn't have enough oomph to do 256 proper. Does TP's solution do DSD512? If so, I'll definitely have a look!

It does do 512, but you need to populate the clocks with 45 & 49 MHz versions. Any higher would maybe be possible if it weren`t for the 100mbit NIC reaching its limits, I assume. It runs rock solid, sounds very organic and transparent and it serves as an NAA. I did replace the smt electrolytics with tantalums. Really nice!

[Marco]

5 hours ago, 4est said:

Are you using a BBB for it then?

AFAIK there`s no other combination possible, as for it to work it needs a Botic driver:

http://bbb.ieero.com/