Open Source DAC R&D Project

[Hurtig]

Time for a new DAC project....

As a response to the growing number of over-priced DIY DAC projects, Kurt von Kubik and me decided, to use the experiences from our Reference DAC, and develop a new DAC.
The idea is that this DAC should match commercial DIY DAC's, which is normally based on Op-Amps.... That's why we will also use op-amps.

In contrast to many commercial DIY DAC's, this one will not just be a DAC-PCB without analog stage and PSU. It will be a full DAC design, including Complete PSU, digital stage and and analog stage. Even connectors onboard.

And in contrast to thoose telling you, that a DAC-board without PSU and analog stage will cost you 300-600$, we are beeing more realistic.
We aim for a total price of 199$ including PCB and ALL components. PSU, DAC and analog stage all included.

Since we do not believe in the idea of seperate boards connected by screw terminals in High End audio, everything is placed on 1 single board! Just plug in 115 or 230 VAC, and you are running!

The project will be 100% open source, with links to component suppliers. Just to give all of you an idea of how low cost such a design really is... Even though some manufactures tell you something different

During the R&D of our Reference DAC, we found that the best performing DAC on the market (Sonic performance), is CS4398 from Crystal Semiconductors. So the choice is really easy... The new DAC will be based on this chip.

We will use CS8416 SPDIF receiver (Market leader) and SRC4192 Sample rate controller.
In general, we will use high quality components, like Wima foil capacitors, Panasonic FM series electrolytics, 1% resistors and so on.... All the things that manufactures try to tell you, will cost a fortune.... Still, our target price is max 199$. And still... 100% open source!!

Since this is a project under R&D, we will accept good ideas.. So keep them comming....

[Hurtig]

This is the Schematic as it looks right now. Be aware that this is a project under R&D. Some values may not yet be correct.
If you have any idea's, please feel free to comment....

[Hurtig]

Don't waste your time on PCB layout for this project! We are busy making a pro layout. And just like the rest of this DAC, the layout will be open source to.

When the design is 100% done, the BOM with links to suppliers will also be public.

[Hurtig]

How about USB interface?? We are a bit doubtful about implementing a USB interface on the DAC.
Basically, an USB interface would make the DAC very flexible. The trend goes towards computer based audio. In that light, USB is almost mandatory.

But then again.... Connecting a PC through a USB connection, will create a galvanic connection between PC and DAC, which will cause massive noise injected into the DAC. That's reality, also in commercial DAC's (Even though they forget to tell you ).

So the question is.... Do we want USB or not??

We could skip the USB part, and add an extra TOSLINK interface. Even though TOSLINK is much worse performing than electrical SPDIF, TOSLINK is much better than common available USB interfaces. And then you are galvanic seperated = No Noise injection from the PC.
This just requires a TOSLINK interface on the PC. But this seems to be more common these days.

What is your opinion on this??

[planet10]

Unless the USB has asyncronous transfer, the DAC becomes limited by the standard TI chip.

Personally i'd like to see a FireWire connection. That would make it interesting.

dave

[Hurtig]

Yeap.... Firewire would be NICE! But we do not want to create something that needs a lot of programming. And that would be the case with Firewire.
I did work on Firewire some years ago, when I was working with R&D at Bang&Olufsen. Trust me... It's not suited for DIY

Also I see the trend moving away from Firewire. It seems like Firewire never really got the foot in.

Maybe we should consider enhancing the performance of the USB interface, since this is more suited for DIY....

[sergery]

Looks good. I like the concept. One thing you might consider for the folks that want to tweak is to make some solder headers for alternative analogue stage connection. That way you have your solution out of the box, which I'm sure will sound good, but the ability to tweak and compare without ruining it as well.

[rsbonini]

Just a couple questions/comments. Why do you have that a zener diode on the spdif input? Shouldn't you have a proper pulse transformer there instead? As for the issues associated with a usb interface, you could overcome this by using an optocoupling stage, either between the computer and the receiver chip or, on the serial data stream from the chip to the DAC. The analogue power supply seems a little incomplete, you seem to be missing some clamping diodes, as well as your sense and return grounds should (ideally) be shown independent. I have a +/- 15V small signal audio power supply design that could easily be used for this project. It includes optically operated solid state relays to switch power to the chips. Also decoupling capacitors on the NE5532's; the 150uf electrolytics could be replaced with 4.7-10uf tantalum for equivalent, if not better performance. You're also using a DAC with balanced outputs, I'd put a couple of OPA1632's to buffer those, and offer a nice set of balanced outputs on this unit as well.

[gaobingic]

Thank you !

[bearberry]

Just reading some articles on computer audio and if I understand correctly, HDMI is about the only way to pass some types of high-resolution audio. But i have no idea how hard it is to implement HDMI input on a DIY DAC...

Thanks for undertaking this project!
bb