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DAC project completed
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Old 9th February 2009, 02:10 PM   #1
Kurt von Kubik is offline Kurt von Kubik  Denmark
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Default DAC project completed

Here´s a few shots of the latest edition of our DAC project.
The Chips chosen are CS 8416 and CS4398.
The supply for the digital section consists of its own transformer (UI core), rectification, smoothing and then 2 LM317 preregulators befollowed by 4 discrete ultrafast regulators, 2 for analog circuitry in the chips and 2 for digital logic.
Filtration is done passively with high quality parallel caps with 2. order slope beginning @ about 100KHz.

The analog section is completely discrete with no feedback loops at all, there is a DC servo circuit though, but this is only ative beneath about 1/10 of a Hz.
The power supply for the analog section features its own transformer (UI core) for maximum isolation, followed by rectification, smoothing and then 4 LM317 preregulators implementet as current generators. They feed 4 shunt regulators which directly feeds the analog section.
In the analog PSU there is only smoothing capacitors before the preregulators, the rest is done by active electronics alone, which results in a very low output impedance and a very wide bandwith without any lift in output impedance.
The less fortunate behavior og electrolytics is this way avoided near the signal path.

This project has been going on for years, actually we started out in 2003 with diffrent chips, but the idea was pretty much the same. The latest addition was actually the shunt regulators in the analog section, which came obout some 6 months ago, from then on, we felt th rightnes of the whole project increasing.

The sound of the DAC is IMHO dazzling. I both owned and tried a lot of digital gear in my system, but I always felt that digital sound was in some way squeesed, and very seldom easy and liquid the way natural sound is.
In fact that was the original problem that inspired us into this project.
At this point we think we reached a peak, where both of us think that refining further will be either at no use or infact risky. The latter because already for example digital connectors, powercords , digital sources, their digital outputs and other auxilaries has become pretty much the limitations.
Much can be said about the sound, but I´m not really the right one to be the judge of my own work. But I can say that the eyeopener of this DAC is Dynamic range (think of that as the ability to recover very low level information), 3D and an effortless way of reproducing all frequenzies with a lot of nuances.

So feel free to have a look

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Old 9th February 2009, 05:34 PM   #2
Hurtig is offline Hurtig  Denmark
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I better introduce myself into this discussion, since I am the engineering part of this project.

As Kurt von Kubik (KvK) says, we have been working on this project for about 5-6 years.

As mentioned, the project started out with some different DAC-chips, mainly Burr-Brown (Burr who?? --> TI).
I have always had some special feelings for the Crystal chips, so we ended up using the top-performer from CS4398.

One of the things we have seen is, that the actual DAC-chip isn't that critical. As long as you use one that is... well... Good enough.

The place where you get the real benefit, is from working intensively with the power supplys, analog stage and PCB layout. The first prototype using the current IC's, ran for the first time around 3 years ago. What have we been doing since then?? Some call i tweaking. I don't know what to call it, but it takes a long time! Anyway... It's all worth!

We have chosen to use seperate UI core transformer for digital and analog stage, followed by low impedance capacitors and special regulator circuits.
Generally we use a 2 stage regulator. First a pre-regulator, using a standard 3-pin regulator. This we remove ripple from the capacitors. The pre-regulator is followed by a low noise discrete regulator, that only has to deal with moving the last noise.

In the analog stage, we use a special combination of a current source followed by a shunt regulator. This allows us to NOT have any capacitors decoupling the analog power rails.
We did a lot of testing different capacitors, before we tried this shunt-version. All capacitors sound different, but it's really hard to find someone that doesn't sound of anything. They all add that little tiny thing. The shunt-regulator simply does not!

In total we have 14 regulators on-board!

The analog stage: Well, we don't like op-amps!! Also... we don't like negative feedback... Therefor we use a fully discrete non feedback design, using low noise transistors and high quality resistors. Btw... We don't like AC-coupling ==> The analog stage is fully DC-coupled.
To avoid small amounts of DC, a DC-servo is mandatory. We decided to go for a very weak version, with a very low cut-off frequence. Actually around 1/30 Hertz.
Naturally the analog stage runs in Class-A. You should feel the heat

The PCB is double sided, and has gotten very much attention! Generally we tned to use GND-planes on both sides, but some strategical places we have guided the GND currents the right way.

Then how does it sound?? As KvK says.... You should not be your own judge.
Anyway... I guess we both agree, that we haven't ever listened to anything like this. May it be an Accuphase, ML, Krell or anything else...

Wanna know some more?? Please feel free to ask!
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Old 9th February 2009, 05:48 PM   #3
hifimaker is offline hifimaker  United States
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Congratulations, your build looks beautiful and very professional. I agree, it takes more time then most realize to tune and optimize a good DAC.

It would be great to learn more about your output buffer, like the topology used and what worked and did not work or fell short.

Old 9th February 2009, 06:29 PM   #4
Hurtig is offline Hurtig  Denmark
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Thanks for the interest!

At the moment we will not go further into the actual scematic... It simply will not make sense. The circuit used here, will not automatically be perfect in another application.

Shoving the schematic at this state, may cause some people to try building a DAC using some of the same circuits, and that may result in great dissapointment. You simply have to "tweak" the circuit to the actual application.

Some things are quite universal, anyhow. You should use:
- Discrete analog circuits.
- Non feedback analog circuits.
- Pay extreme attention to the power supply.

One thing that many people mis-judge, is the third line, anout paying attention to the power supply.
Often people equals this, to making an over extreme large power supply. And that is NOT whats needed. You need to "work smarter, not harder". The more and bigger capacitors you use in the analog stage, the more they will add to the sound.
Old 9th February 2009, 08:37 PM   #5
DavidJE is offline DavidJE  United Kingdom
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This looks like a fantastic piece of work! Congratulations on completing it.

I'm currently thinking about buying a DAC. Are you planning on manufacturing and selling these DAC's to the public? If you are, what price will they be for UK customers?


Old 10th February 2009, 06:09 AM   #6
Hurtig is offline Hurtig  Denmark
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Hi DavidJE
Thanks for the nice words...

We have not yet decided if and how to sell it.

The project started 5-6 years ago, as a hobby project, since both KvK and me had an idea, that digital audio was far from it's potentials.
Currently we are working on a chassis....

But... we don't want to keep this project for our self. We both feel, that as many people as possible should have the chance of enjoying the result of our thousands of hours of working.

About the price, if we do sell these.... Well, I really don't know yet. But it will follow my intention having most "bang for the buck"!
And this will be the case! The parts for this DAC really isn't that expensive, even though we use the best available. Only High End manufacturers have the x20 button on their calculator :D
Old 10th February 2009, 06:21 AM   #7
Cauhtemoc is offline Cauhtemoc  Sweden
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It looks very well made. I can't say I agree with your choice of SPDIF receiver and DAC, but it's very well made nonetheless.
Old 10th February 2009, 06:39 AM   #8
anli is offline anli  Russian Federation
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I don't understand the thread intention (except for "hey, we are great!") as long as the schematics is hidden. Do you? Are all those common words about "right way" new for anybody?
Old 10th February 2009, 07:22 AM   #9
analog_sa is online now analog_sa  Europe
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If you do intend to manufacture and sell to diyers make sure the digital and analogue boards are separate. This is obviously a compromise but i can't honestly see many orders for the digital part. And no, most of us do not believe "that the actual DAC-chip isn't that critical".
Old 10th February 2009, 09:21 AM   #10
Bernhard is offline Bernhard  Germany
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Default ... mine is bigger than yours ...

Originally posted by Hurtig

In total we have 14 regulators on-board!
Please count the heatsinks

14 shunt regulated rails for the DAC share the voltage reference and the driver rails that are provided by the additional two shunt regulators.

Those two shunt regulators together with the voltage reference form a secret system wherein the regulators provide the clean rails for the reference IC and its own driver stages, while the reference IC provides the stable reference voltages for its own shunt regulated supply.

Excuse the messy wiring, it is still a (working) test setup.

Click the image to open in full size.

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