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Open Hardware 1-bit multi-level DAC

Miska

Entry posted by Miska

In response to endless DSD arguments here at CA I promised to publish an open hardware design of 1-bit multi-level DAC without magical black boxes. No DAC chips. No camel-back DSD ultrasonic noise bumps either, even with 7th order modulators. Multi-level, but still 1-bit. How is that possible? Well, it's not a secret and I wanted to put it out in an open way. A DAC that is not trying to play dual-role between it's PCM-to-SDM and DSD.

 

Moving most of the DSP things to software, having only minimal amount of digital logic in hardware and all visible at a glance on schematics. It was supposed to be as simple as possible but not any simpler.

 

I decided to use Amanero Combo384 USB interface as plug-on daughter card for interfacing purposes because it is nicely available and supports the needed DSD rates up to 24.576 MHz.

 

This version is by no means final, it is first version of what I came up within a month (simplified from my earlier protos). I will make updates to the design to improve it. And yes, I know, there are many ways to improve this further. This one was intended to be minimal "discrete" implementation without programmable logic or anything. Minimizing board space, number of layers (just two), minimal SMDs, minimal number of components that are easy to obtain, and low cost. But still decent performance.

 

Since it is an open hardware design, improvement suggestions and contributions are welcome. :)

 

Enough of excuses and disclaimers... This is how rev.A boards look like:

<p><a href="/monthly_2014_04/dsc1-a.jpg.4210891f0f95d28f0f4a197399277e8b.jpg" class="ipsAttachLink ipsAttachLink_image"><img data-fileid="28242" src="/monthly_2014_04/dsc1-a.jpg.4210891f0f95d28f0f4a197399277e8b.jpg" class="ipsImage ipsImage_thumbnailed" alt=""></a></p>

Direct 1-bit, 33-level conveter.

 

And here you can find the most up-to-date design documents.

 

P.S. And maybe there'll be DSC2 with all the imaginable high-end bells and whistles, but still no black boxes. ;)<p><a href="/monthly_2014_04/dsc1-a.jpg.b403085a73a11ad2c2daa7a45f8dcc92.jpg" class="ipsAttachLink ipsAttachLink_image"><img data-fileid="28492" src="/monthly_2014_04/dsc1-a.jpg.b403085a73a11ad2c2daa7a45f8dcc92.jpg" class="ipsImage ipsImage_thumbnailed" alt=""></a></p>

9 Comments

Recommended Comments

Superdad

Bravo Jussi! A great start.

 

I'm not a big opamp fan, but you have chosen well, and this is a nice, affordable demonstration of a multi-level, high-speed "chip-less" DSD DAC. How does it sound?

 

I'll have John Swenson explain some of your design to me. Very interested in your reconstruction filter.

 

From your web site it looks like 5.6448MHz (DSD128) is minimum point of entry. Besides getting to that--or preferably much higher (i.e. 11.2896 or 24.576) with HQPlayer, will the Amanero and your DSC1 accept DSD64 or DSD128 from say a Mac with Aurdirvana? I am assuming that DoP is not handled at all.

 

Looking forward to interesting discussions about your design and to learning more!

 

Best,

Alex C.

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Synfreak

Congratulations!

If I had the skills, I would immediatly jump on it, as it would be an interesting experience for sure.

Keep us posted ;-)

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Miska
I'm not a big opamp fan' date=' but you have chosen well, and this is a nice, affordable demonstration of a multi-level, high-speed "chip-less" DSD DAC. How does it sound?[/quote']

 

Opamps save board space and reduce complexity, and given these ones I don't think it would be easy to make discrete one with better performance. I didn't do much listening yet, because I powered it up first time only couple of days ago... :)

 

And it's still missing case, so that's next item I need to find. I did some measurements and it looks promising, but I don't publish those results because it was made without case and with wiring mess. I'll make proper ones when the device is in a proper case.

 

I'll have John Swenson explain some of your design to me. Very interested in your reconstruction filter.

 

From your web site it looks like 5.6448MHz (DSD128) is minimum point of entry. Besides getting to that--or preferably much higher (i.e. 11.2896 or 24.576) with HQPlayer, will the Amanero and your DSC1 accept DSD64 or DSD128 from say a Mac with Aurdirvana? I am assuming that DoP is not handled at all.

 

Looking forward to interesting discussions about your design and to learning more!

 

It will accept any DSD (PCM will mute it to avoid nasty noise). Amanero supports DoP up to 6.144 MHz. For higher rates ASIO driver on Windows is needed. Recommendation is to use at least DSD128 because:

There are two reconstruction filters, an analog CIC filter where cut-off frequency is determined by the sampling rate and a Sallen-Key filter with fixed cut-off frequency. These two form a combination and has been optimized for DSD256+ rates while also DSD128 still gives OK results. This way, both frequency and phase response stay within nice bounds while providing practically flat noise floor performance.

 

For DSD64 playback, HQPlayer can upsample DSD64 to higher rates.

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matthias

Miska,

 

Congratulations!

I am looking for a pureDSD DAC for years. I asked already on the forum if there is a chance to get your DACs as a assembled and tested module for the not advanced in DIY. Would be very much appreciated. Please, please think about it!

 

Thanks

KR

Matt

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Jud

Miska, this looks very interesting. One of these days I think I might be inclined to try building it, though at the moment I and the fellow who's making the chassis are in the final stages of work on my semi-customized DAC. Last evening he attached some copper ribbon I got from the folks at Omega-Mikro to the outputs with ridiculously tiny (00-90) screws and washers O-M supplies for the purpose, and the process was sufficiently painstaking I am exhausted just from watching him! So the prospect of good sound at relatively low cost makes me eager to do some DIY, but not right now. :)

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Ipoci

Great Miska !

 

I'm currently working to have a PCB productized by a friend.

 

As you know I'm also actively working to have HQ Player NAA board build over Acqua A5 so my final goal is having NAA directly sending traffic to DSD-DAC via I2S interface and skip the ugly USB …

 

Cheers. Massimiliano

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luismc

A very interesting project, Miska.

 

I have a question.

 

What tolerances are required in Resistor Networks? and in filter parts?

 

Regards.

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Miska
What tolerances are required in Resistor Networks? and in filter parts?

 

Networks are just normal 2% Bourns type and used to save a lot of board space. All normal resistors are 1% metal-film, except 1W 5% carbon-film resistors used for the PSU LEDs. Filter capacitors are polypropylene (Wima) and 5% in my case because the normal 2.5% I use was out of stock. 220p output stage compensation cap is C0G ceramic, but could also be polypropylene. All PSU rail 100n bypass caps are X7R ceramic. I used 2N3904 for driving the output relay again due to out of stock situation.

 

Output stage gain resistor could be for example 1k depending on sensitivity of the amp inputs.

 

I'm now experimenting with slight modifications to the I/V stage, with possibly 1 - 3 components added.

 

Inverter is 74VHC04 in my build, because I happened to have it. I'm using 5V VDD and for that case the AHCT595 is crucial because it works with 3.3V CMOS input levels while running from 5V supply... For 3.3V VDD there are many options...

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