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Old 20th February 2013, 04:30 PM   #1
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Default Designing a DAC, help with chip selection? WM8740 or WM8523

Hi Guys, first post here,


So i decided the other day that i wanted a DAC and to stop using my motherboards line out. Saw that they were expensive and have been thinking about making one ever since.

So my first port of call was to select a chip for the DAC, i chose the Wolfson WM8740 (Cambridge Audio DAC Magic is based on this). Then i needed to select a USB Audio controller chip with i2s output.

I found the CP2114 which has some gpio pins for configuration, and has some configurations built in for specific DAC's. I noticed the Wolfson WM8523 in this list and thought id check it out, the only difference i can see with the 2 DAC chips is that the WM8523 has line out, rather than (LP, LN, RP & RN) (which certainly simplifies things) a SNR of 106dB vs 123dB & finally is a fraction of the price.

Am i missing something here as the 8740 seems very popular but the 8523 is certainly from what ive seen the more desireable chip. Any advice or reccomendations are welcomed. Also I do not have my heart set on wolfson chips.

Look forward to your responses and hope this forum can help me now and later if i get stuck later in the design process.

Thanks,
Oliver

NOTE:

the CP2114 supports the following chips in its built in configurations: CS42L55, WM8523, PCM1774
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Old 20th February 2013, 04:41 PM   #2
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Infact what im really asking is does anyone know anything about configuring the CP2114 as i understand that this is done in some write once ROM, but i can't find anything about how to configure in the data sheet.

If you guys really think the 8740 is better that is what id prefer to use and the data sheet has good designs for Differential output filter so that is not actually an issue at all to me.

Another field i know nothing about and will welcome knowledge is any tips for power supply?
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Old 21st February 2013, 03:38 AM   #3
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When you say DACs are expensive, have you been looking on eBay recently? If you value your time then a DIY DAC will work out much more expensive than buying one online. I've designed DACs myself in the past (professionally) so I know this from experience - these days I'll start with a ready made one
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Old 21st February 2013, 09:51 AM   #4
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Wheres the fun in that.
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Old 21st February 2013, 10:04 AM   #5
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coaxial DIR9001 + WM8740DAC decoders USB + coaxial G-1 | eBay

I have found this which is essentially what I want.

It would be cheaper still to buy one of those to base a design off and then build my own than it would be to buy a professional level product such as Cambridge Audios DAC Magic 100.

If that bloke on ebay can sell what i want for 30 then I can certianly design and build one for less, this is meant to be a free time hobby project not something i just go blow some money on.

And to be honest if i design something that i'm happy with, i will possibly consider 3d printing some enclosures and making some to sell on ebay.
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Old 21st February 2013, 12:39 PM   #6
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Best results would be with a proper multi layer PCB design, that would be a reasonable cost, with SMD components such as decoupling caps.
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Old 21st February 2013, 12:47 PM   #7
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Quote:
Originally Posted by olig1905 View Post
If that bloke on ebay can sell what i want for 30 then I can certianly design and build one for less, this is meant to be a free time hobby project not something i just go blow some money on.
What makes you so sure? If you need a PCB, then what PCB house is going to do you a single PCB for that kind of money? It would probably take you the best part of a week's work to lay out the PCB. Then if you check out the kit of parts, getting small quantities from Mouser or Farnell would comfortably exceed 30, excluding the delivery charges.

To answer your question about the fun - it comes from making it sound better, these boards tend to be quite lack-lustre sound-wise.
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Old 23rd February 2013, 06:23 PM   #8
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I can see i m going to get no help here then, well at least not from you. I refer new readers back to my OP.

I want to do this out of interest and to see what i can make myself. If it takes me a year to complete and it sounds **** well, then at least i will have had fun for a year!
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Old 24th February 2013, 12:18 AM   #9
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Quote:
Originally Posted by olig1905 View Post
I have found this which is essentially what I want.
....
If that bloke on ebay can sell what i want for 30 then I can certianly design and build one for less, this is meant to be a free time hobby project not something i just go blow some money on.
If that's what you want then buy it. You won't be able to replicate that design on your own for less. I doubt you could do it for even 4x buying minimum quantifies from US or European suppliers. Have you priced PCB fabrication?

I think if you are willing to devote a year of your life to designing a DAC you ought to set your sights higher than a PCM29** equivalent.
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Old 26th February 2013, 09:31 PM   #10
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Quote:
Originally Posted by olig1905 View Post
coaxial DIR9001 + WM8740DAC decoders USB + coaxial G-1 | eBay

I have found this which is essentially what I want.
For what it is worth:

A) I just received that exact DAC (from the same seller) yesterday and it sounds awesome. Pull the OP275 out of it and stick in an AD8599 and things get really great. I am feeding it with a CM6631A-based USB/SPDIF converter (from the same seller).

b) This new DAC replaced a WM8524-based DAC, which is certainly a much simpler design (no opamps needed, etc.), but the 8740 sounds considerably better to my ears.

The best part is I bought the CM6631A board and the WM8740 board for considerably less than I paid for my WM8524-based DAC. I think you would have trouble building something cheaper, and it will almost certainly not sound as good as what zoe is selling.
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