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Old 25th January 2010, 06:34 AM   #1
Chris_F is offline Chris_F  United States
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Default Designing an External DAC

I'm wanting to build an external DAC / Headphone amp for use with my computer. I haven't got much experience with analog circuits, so amps aren't my thing, but I am pretty good with digital circuitry.

I wouldn't call myself an audiophile, but I'd like to design this so that just about anyone would be envious. I'm wanting it to support 192KHz 24-bit from head to toe and have both SPDIF and USB audio input.

Some of the parts I was considering are:

Cerrus Logic CS8416 or Wolfson WM8804 for the SPDIF receiver

PCM1792/3/4/8 or PCM1704 or CS4398 as DAC

I'd love to get some suggestions. Also, I have no idea what to do about a 192/24 USB input. I saw a Cmedia chip (CM6620) that is said to support it, but I can't find anyplace to purchase these, and there are no datasheets available.
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Old 27th January 2010, 03:31 AM   #2
Chris_F is offline Chris_F  United States
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Are people avoiding this topic like leprosy, or is it that nobody with any knowledge has seen this thread?
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Old 27th January 2010, 03:51 AM   #3
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No, we're not ignoring you

From what I read, you are asking for a schematic for a circuit with very specific requirements. No one has made this specific device and so there are no replies.

However, you will find several designs very similar to what you request and maybe one will be a good compromise. Maybe one will even have a PCB that you can buy.

Try searching the forum for the chip numbers you are interested in. This will generate 100s of threads to read. If you need more info than post in those threads.

Good luck!
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Old 27th January 2010, 04:36 AM   #4
Chris_F is offline Chris_F  United States
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Quote:
Originally Posted by Iain McNeill View Post
No, we're not ignoring you

From what I read, you are asking for a schematic for a circuit with very specific requirements. No one has made this specific device and so there are no replies.

However, you will find several designs very similar to what you request and maybe one will be a good compromise. Maybe one will even have a PCB that you can buy.

Try searching the forum for the chip numbers you are interested in. This will generate 100s of threads to read. If you need more info than post in those threads.

Good luck!
Woah, wait a second. I'm NOT asking for any schematics. I (ME) am the one designing this DAC. I simply want some input on my design choices. I can make my own coper PCBs or I can order a 4 layer from a company like PCB123. My prototype will probably be on some cheap radioshack potoboard.

I listed some part numbers I was interested in, but am not 100% which to use. The CS8416 and WM8804 both look like equally good recievers. I can find posts on both, but none that directly size the two of them up to eachother.

PCM179* look like some good DACs, as does the PCM1704 and CS4398. I know a lot of it is probably personal prefrence, but I'd take any advice people might have.

Like I mentioned, one major roadblock that i could use some help with is finding a USB 2.0 audio reciver that can handle 192/24. Most seem to do no more than 48/24, with maybe a few 96/24 here and there.

I was also toying with the idea of throwing in a Spartan-3A DSP FPGA for EQ and reverb effects. That's if I can get the rest of the design figured out.
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Old 27th January 2010, 04:57 AM   #5
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as Ian points out, there are hundreds of threads already on precisely these questions. Do a bit of searching, and you will be rewarded.

Some prefer the CS4398, some prefer the TI/BB chips. Yet more again quite like the wolfson parts.

You likely can't go wrong with any one of them. Decide if you want voltage or current out. Then pick one and run with it. The quality of the supporting power supply and analog stages may far out weigh any difference between the chips. Most of the important bits of the completed DAC are analog, so start brushing up

good luck!
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Old 27th January 2010, 06:48 AM   #6
Hurtig is offline Hurtig  Denmark
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Great project! I know how much fun such a project can bring you.

We (Me and KvK) have been through this the hard way. We started up with PCM1704-K, going to PCM1794.... But we ended up with CS4398 from Crystal Semiconductors. Quite unusual for an high end DAC. But it simply blew away all others on pure sonic performance.

But be aware, that making a good DAC, will take a long time. It will take you a week or 2 to have something running. But it took us 4 years of tweaking, before we we 100% satisfied. All good for thoose who wait ;-)
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Old 27th January 2010, 07:18 AM   #7
Chris_F is offline Chris_F  United States
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Thanks for all the posts so far. I have no doubt that this will be a fun project, and hopefully I'll get a nice DAC out of it to use with my computer.

I'm still working my way though archives of other posts. Can't even count the pages I've read, will read. Anyone have some general design concepts/features that could be implemented to increase fidelity?

Also, still searching for a means of 192KHz/24-bit over USB 2.0
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Old 27th January 2010, 07:28 AM   #8
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New USB 2.0 Audio controller from VIA

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community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
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Old 27th January 2010, 04:52 PM   #9
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Quote:
Originally Posted by Chris_F View Post
Also, still searching for a means of 192KHz/24-bit over USB 2.0
Not aware of anything yet.

Quote:
Originally Posted by planet10 View Post
Wow!
I'm hopeful. However I've had 2 issues with VIA in the past. delayed ship dates and horrible or complete lack of driver support. It will be interesting to see how they fare on this. (it isn't as complex as an entire CPU/northbridge maybe it will go smoothly)

Thanks for the link
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Old 27th January 2010, 06:13 PM   #10
ilimzn is offline ilimzn  Croatia
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Quote:
Originally Posted by Chris_F View Post
I'm wanting to build an external DAC / Headphone amp for use with my computer. I haven't got much experience with analog circuits, so amps aren't my thing, but I am pretty good with digital circuitry.

I wouldn't call myself an audiophile, but I'd like to design this so that just about anyone would be envious.
Unluckily for you, designing a DAC requires a lot of knowledge on analog design as most of it (power, outputs, filters, grounding, parts of the SPDIF receiver) is analog. So, i think you will have to study and experiment in those areas before anyone can be envious. Without this your choice of parts pretty much does n ot matter as it in itself is no guarantee - even the best part used incorrectly will not perform well.
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