Anyone want to design a high end USB DAC?

[bg4533]

We have had a few DAC related projects lately and there seem to be some talented people around here. Guzzlers USB DAC looks nice, but is designed for portable use. Personally I would like a high end DAC for home use. Something designed without many compromises, wall powered and ideally with both SPDIF and USB inputs.

How much interest is there for something like this? Anyone willing to take on the project?

 

[DaKi][er]

Funny that you ask, as i've been working on such a thing for the past month or 2 and am expecting the first prototype board to come back from the boardhouse at the end of the week

i have dropped these pictures around here a few times now, but here they are again
Schematic
Board
3D Render

now this is exactly what i've got getting made, but if you want any further ideas implemented then i'm open for suggestions

if you really want to go all out on it, the weakest part of my design would be the analog psu end with them lm7815,7915, etc. that i have been thinking of updateing to something a bit more suitable that will go with the rest of the DAC (something like whats in here -http://www.diyaudio.com/forums/showthread.php?s=&threadid=22205 )

ohh, and i hope you like smd

 

[Magsy]

I have been hoping something like what dakiller has just posted to turn into a pcb group buy for a while

I'm in if anything gets produced!

 

[00940]

What I'd see as nice to have on a "high end" USB DAC is:

- isolation xformer to isolate the usb receiver, which would be bus-powered
- AD1896 to kill jitter and allow for gentle analog filtering
- very low jitter local clock
- discrete I/V
- reg101 regulators all over for 3.3 and 5V voltages, at least LM317 for the output stage
- balanced and unbalanced out
- if possible no output caps
- no more than two power transformers

 

[wistily]

...And asynchronous communication with the PC with a buffer

 

[00940]

Asynchronous transfer is out of reach for diyers. It could be done, perhaps, if you take the receiver and digital control section of the new creative USB soundcard.

 

[Akku]

I really like this project. I was waiting for a DIY hi-end DAC using 1704. I second 00940 suggestions, specially discrete I/V, jitter control, USB isolation and regulation (why not a jung-like reg. implemented on the board?).
I do not have any skill to help you in the design but I will be in for the PCB's

 

[dr_digits]

I've been hoping to build one too. I've been waiting to see how DaKi][er's DAC turns out. I would definately be in for any DAC that has spdif, toslink, and usb and sounds good. The PCM1704 sure looks nice too.

 

[DaKi][er]

I know you have done some work yourself on boards 00940, but just considering modifying my board layout for now with your wish list -

isolation xformer to isolate the usb receiver, which would be bus-powered
Easy to change to that, just something very similar to the guzzler's usb-spdif board

AD1896 to kill jitter and allow for gentle analog filtering
I’ll have to look into that but I’m sure it would be easy to add

very low jitter local clock
Someone can help me with that, I was just going with the clock that the PLL circuit in the cs8416 receiver to run it as that was easy to understand for me

discrete I/V
There are quite a few designs for them out there and it swamped me a bit and I was left a little confused, so just sticking the stock one out of the datasheets on there I added pin headers to bypass them and experiment with other I/V's but if you know of a good one to just stick with, I’ll go for that

reg101 regulators all over for 3.3 and 5V voltages, at least LM317 for the output stage
I got reg102's for all the digital side, the reg101's are pin compatible after checking and both their performances are very similar with the 101's having a little less noise and only 100mA instead of 500mA
So you could use reg101's just fine as far as I can see

Analog side, you need +/-5v for the dac and there aren’t many good quality negative regulators at all and the current psu section on it right now is I’d admit a bit of a slap up at the end job but I do have in mind putting on what is used in the $17K Mark Levison dac as described here- http://www.diyaudio.com/forums/showt...threadid=22205
And for whatever the I/V requires make it up with lm317's or some lower noise types as you can get away without negative regs for this as the transformer has dual secondaries

balanced and unbalanced out
This is quite easy to do with the pcm1704's as there is an invert pin that will invert the incoming digital signal giving you balanced outputs if you use 2, and just having extension boards for this that stack over the current pcm1704's as now it would work well as far as I can see giving the option to run either

if possible no output caps
Well most dac's need a low pass filter after the I/V to get rid of the real high frequency noise, so it’s a bit hard to do without them but at least it is real small value ones that you can use polypropylenes or silver mica for

no more than two power transformers
I only got 2 so far, their mini ones from digikey and fit quite snug in the Hammond case its all going in

 

[00940]

For the output caps, I was more thinking of the big caps needed to get rid of offset, of course you need at least one filtering cap.

For the -5V of the dac, consider the LT1964.

Don't take my "wishlist" too seriously. I won't be able to participate in this, since I really need a balanced out DAC and 4 pcm1704 and 2 ISO150 would push me near 150$ (once vat added).

Using an AD1896, the clock system is quite easy. Your CS8416 is master, sending about anything you want into the ad1896, we don't really care, let's say 44.1/16bits (the most probable frequency coming from the usb receiver). The AD1896 is also slave on its output, receiving a system clock of 24.570MHz. It is configured to output 24bits, 96KHz, 256Fs. The following DF1706 is also clocked by that system clock. It allows you to get the full 768KHz the PCM1704 is capable of.

 

[DaKi][er]

Quote:

Originally Posted by 00940 For the output caps, I was more thinking of the big caps needed to get rid of offset, of course you need at least one filtering cap. For the -5V of the dac, consider the LT1964. Don't take my "wishlist" too seriously. I won't be able to participate in this, since I really need a balanced out DAC and 4 pcm1704 and 2 ISO150 would push me near 150$ (once vat added). Using an AD1896, the clock system is quite easy. Your CS8416 is master, sending about anything you want into the ad1896, we don't really care, let's say 44.1/16bits (the most probable frequency coming from the usb receiver). The AD1896 is also slave on its output, receiving a system clock of 24.570MHz. It is configured to output 24bits, 96KHz, 256Fs. The following DF1706 is also clocked by that system clock. It allows you to get the full 768KHz the PCM1704 is capable of.

Yea, I’m not one to go chucking electrolytic in the signal path if I can help it

I’m likening the idea of the AD826 and LT1027 for the +/-5V with separate ones for each dac but with them sharing the one LT1027 5v reference, from other reports it is meant to sound very good paired with the pcm1704's and I’ve been playing around with them on the layout of it on the dac since last week

I’m not keen at all on the idea of re-sampling the signal at all and i think a few others would be against that as well

And I understand how much the pcm1704's cost, they were a good chunk of the cost of the whole thing and I didn’t even get the expensive 'K' version

I think they were the 2nd most individually expensive part after the PCB

 

[Garbz]

why do I get the feeling as soon as I finished mine I'll end up joining the group buy and building yours :S

 

[DaKi][er]

Quote:

Originally Posted by Garbz why do I get the feeling as soon as I finished mine I'll end up joining the group buy and building yours :S

It is inevitable, why resist?

 

[Garbz]

and then when i compare them side by side and mine turns out to be better what u going to do

 

[DaKi][er]

I didn’t order the boards, a friend go a whole panel done and had some room to add mine in as well, so the other boards in there aren’t mine
Its getting sent to me express post tomorrow morning so fingers crossed I get it Friday