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Electronics => Open Source Hardware => Topic started by: Antipixel on July 17, 2016, 11:44:34 am

Title: Looking for an Open Hardware DAC
Post by: Antipixel on July 17, 2016, 11:44:34 am
TLDR;

Looking for an open source hardware DAC plan or someone who built their own DAC and has mad ideas :D

Long version:
Was looking for a DAC, AMP, and a Speaker for a long time now. But none fit my needs... till it dawned upon me... I study physics, I can wield a soldering iron... build your own!

So my current idea is to build my own easily fixable box with all of that jazz in + an audio jack for headphones. (All the details will trickle in with onsetting problems)
But as much as I like reinventing warm water, I do need to also finish my degree. So I'd love it if someone has a template or tips how to deal with it so I'd only have to reinvent the parts I'd need specific for myself.
Of course I'd post my progress and plans in the end.

PS: Tips about components are welcome :D the ones I had to deal so far were accademic, and perfect, and on paper
Title: Re: Looking for an Open Hardware DAC
Post by: blueskull on July 17, 2016, 12:09:50 pm
What do you mean open hardware DAC? You mean open source DAC from IC implementation? That's gonna be hard, even implemented in FPGA.
Title: Re: Looking for an Open Hardware DAC
Post by: Kalvin on July 17, 2016, 12:18:05 pm
The sound will get distorted as soon as it enters into the crossover filters and leaves the speakers.
Title: Re: Looking for an Open Hardware DAC
Post by: chickenHeadKnob on July 17, 2016, 12:19:58 pm
You mean something like this? https://hackaday.io/project/5996-drdac-usb-audio-dac (https://hackaday.io/project/5996-drdac-usb-audio-dac)
Title: Re: Looking for an Open Hardware DAC
Post by: Antipixel on July 17, 2016, 12:38:11 pm
@Blueskull Ya it sounds hard but if I want it to be tidy and not have 3 boxes on my desk or butcher the parts of 3 boxes and somehow squeeze them in one functioning box. Unless you have a better idea Im ears to everything at this point really.

The sound will get distorted as soon as it enters into the crossover filters and leaves the speakers.
Elaborate on this.

You mean something like this? https://hackaday.io/project/5996-drdac-usb-audio-dac (https://hackaday.io/project/5996-drdac-usb-audio-dac)
Something exactly like that.
Title: Re: Looking for an Open Hardware DAC
Post by: Kalvin on July 17, 2016, 01:02:27 pm
The sound will get distorted as soon as it enters into the crossover filters and leaves the speakers.
Elaborate on this.
Even if the DAC and the amplifier are close to Perfect, the crossover filter will create phase/time error and the speaker elements with the enclosure will add their own artefacts [which are definitely audible by every person with golden ears, of course]. Most of the amplifier designs are driving the inductive speaker elements in voltage mode which may not produce ideal response either.

Here is a nice article about the crossover filters, phase error and time error: http://sound.westhost.com/ptd.htm (http://sound.westhost.com/ptd.htm)
Here is a nice summary about the speakers and the current-drive mode by Tomi Engdahl: http://www.epanorama.net/newepa/2014/10/10/loudspeaker-operation-current-drive-better-than-voltage-drive/ (http://www.epanorama.net/newepa/2014/10/10/loudspeaker-operation-current-drive-better-than-voltage-drive/)

Disclaimer: I am not an expert by any means and I do not have golden ears.

Edit: Added the link to Tomi Engdahl's article.
Title: Re: Looking for an Open Hardware DAC
Post by: NiHaoMike on August 28, 2016, 06:51:20 pm
If you're just looking for something to run some headphones, my best friend and I came up with this:
https://github.com/NiHaoMike/OpenDAC-HD

If you also want to use speakers, things get a lot harder. I do not know of any DIY purely digital amplifiers and adding digital crossover makes things harder still.
Title: Re: Looking for an Open Hardware DAC
Post by: ip2k on October 20, 2016, 02:05:45 am
Check out the Henry Audio DAC. In general though, as others have said, implementing one from scratch or on something like an FPGA is going to be Difficult. If you'd like to try that route, check out FPGA4Fun 's One-Bit DAC.


Sent from my iPhone using Tapatalk
Title: Re: Looking for an Open Hardware DAC
Post by: Harrkev on December 07, 2016, 06:42:23 pm
If you want to go COMPLETELY open-source, there is always the resister ladder.  Getting 16 bits of resolution might be a bit of a pain, but certainly doable...

https://en.wikipedia.org/wiki/Resistor_ladder
Title: Re: Looking for an Open Hardware DAC
Post by: Lukas on December 07, 2016, 11:53:41 pm
You may also want to take a look at this: http://nwavguy.blogspot.de/2012/04/odac-released.html (http://nwavguy.blogspot.de/2012/04/odac-released.html)
Title: Re: Looking for an Open Hardware DAC
Post by: NANDBlog on December 16, 2016, 12:48:55 pm
You may also want to take a look at this: http://nwavguy.blogspot.de/2012/04/odac-released.html (http://nwavguy.blogspot.de/2012/04/odac-released.html)
He never released the design files. Also he disappeared some 2 years ago, such a shame.
If you're just looking for something to run some headphones, my best friend and I came up with this:
https://github.com/NiHaoMike/OpenDAC-HD
That thing looks quite resonable, when I read the used ICs and the schematic. Then I looked at the implementation  :o
Good job  :-+
Title: Re: Looking for an Open Hardware DAC
Post by: HSPalm on March 09, 2017, 09:49:42 am
@Blueskull Ya it sounds hard but if I want it to be tidy and not have 3 boxes on my desk or butcher the parts of 3 boxes and somehow squeeze them in one functioning box. Unless you have a better idea Im ears to everything at this point really.
So you're looking for an IC implementation like Blueskull suggested.

You mean something like this? https://hackaday.io/project/5996-drdac-usb-audio-dac (https://hackaday.io/project/5996-drdac-usb-audio-dac)
Something exactly like that.
So you're not looking for an IC implementation after all.

Many who's in audio say DAC and mean the whole implementation, from input connectors (USB often), through the actual DAC (the ic), further on through an amp and then out to speakers or headphones via connectors again. Looks like this is the case here.

You mean something like this? https://hackaday.io/project/5996-drdac-usb-audio-dac (https://hackaday.io/project/5996-drdac-usb-audio-dac)
About this, I admire the bodge-job on the DAC ic!
Title: Re: Looking for an Open Hardware DAC
Post by: ECEdesign on April 08, 2017, 02:29:45 pm
You can read the literature on DACs.  To make one you need a CAD tool like Cadence and the money to send your design to a foundry.  Usually, only companies and well-funded universities have this kind of money since you can reach one million pretty quick.  Better off just buying an off the shelf DAC and learning a bit about how DACs work.
Title: Re: Looking for an Open Hardware DAC
Post by: tiger99 on August 07, 2017, 10:35:07 pm
A 16 bit DAC will cost you maybe a few pounds, dollars or Euros. A 16 bit R-2R DAC made at home will not be monotonic and so will cause horrible distortion. A string DAC made at home will be monotonic but not necessarily linear, unless you build it with Vishay S series resistors, of which you will need 65535, all of one value, at about 7 pounds/euros/dollars each, and at least 4096 16 bit analogue multiplexers plus decoding logic.

You CAN make a PWM DAC at home, and it can be highly accurate and linear, but it will need time resolution of about 350 picoseconds to cover the audio band with 16 bit resolution. You would need a FPGA with a phenomenal clock speed and minimal jitter. It will also need a well-designed low pass filter, which is entirely feasible as it involves op amps and only moderately precise (say 1%) resistors and capacitors, and only a handful of each.

A PWM DAC is supremely useful for low frequency instrumentation, where the superb linearity probably can't be beaten, and is a technique worth learning about, but is just not going to be useful for audio.

So basically you can't beat, or come anywhere near to, a moderately priced chip from any of the major semiconductor manufacturers.
Title: Re: Looking for an Open Hardware DAC
Post by: blueskull on August 07, 2017, 11:09:17 pm
A 16 bit DAC will cost you maybe a few pounds, dollars or Euros. A 16 bit R-2R DAC made at home will not be monotonic and so will cause horrible distortion. A string DAC made at home will be monotonic but not necessarily linear, unless you build it with Vishay S series resistors, of which you will need 65535, all of one value, at about 7 pounds/euros/dollars each, and at least 4096 16 bit analogue multiplexers plus decoding logic.

You CAN make a PWM DAC at home, and it can be highly accurate and linear, but it will need time resolution of about 350 picoseconds to cover the audio band with 16 bit resolution. You would need a FPGA with a phenomenal clock speed and minimal jitter. It will also need a well-designed low pass filter, which is entirely feasible as it involves op amps and only moderately precise (say 1%) resistors and capacitors, and only a handful of each.

A PWM DAC is supremely useful for low frequency instrumentation, where the superb linearity probably can't be beaten, and is a technique worth learning about, but is just not going to be useful for audio.

So basically you can't beat, or come anywhere near to, a moderately priced chip from any of the major semiconductor manufacturers.

Welcome to the world of sigma delta modulation. With some solid knowledge in DSP and FPGA, it's not that hard to get 18 useful bits, and with some good calibration tricks, 20 bit should be fine.

True 24 bit is not yet achieved by any audio grade chips, even those so called 32 bit chips, but with careful enough design, there are very few true 22 bit chips, namely parallelled PCM1792A and Sabre Ultra (which is based on HyperStream technology, internally parallelled).
Title: Re: Looking for an Open Hardware DAC
Post by: gagrdonik on August 13, 2017, 10:36:46 am
Thanks for this link, it's really helpful for me