CHANGSTAR: Audiophile Headphone Reviews and Early 90s Style BBS

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Author Topic: slimline dac with the AK4396, and an XMOS USB receiver (>= 384 PCM/64/128 DSD)  (Read 17059 times)

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Peef

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Thanks for the schem! Are you sure about the values for the third order filter though? I calculated its transfer function and it's nothing like the second order implementation - the -3dB point is around 400Hz, and it's not unconditionally stable, assuming a source impedance of 30R + R1. The second order implementation seems much better, as you said.

Have you considered bypassing the R8/C1 (and equivalent on V-) power supply filter as well? Assuming you have a good power supply, all it would do really is increase the power supply's impedance. I think you might be better served by some carefully placed and derated np0 or c0g SMD ceramic decoupling caps to ensure the supply's stability. A big electrolytic won't be of much use past a few hundred kilohertz. If you want to do something really nuts, you could pick a cap that will have a self resonant frequency equal to the DAC's sampling frequency to improve its rejection and further reduce IMD.

There's an excellent paper on EEtimes on bypassing supplies that I can't find for the life of me. If you haven't seen it, this application report from TI is also pretty great.
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Solderdude

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C3 should be 2.2nF instead of 2.2uF  ;)

2nd order = 124kHz (-3dB) = 72kHz @ -0.5dB
3rd order = 124kHz (-3dB) = 43kHz @ -0.5dB

with C3 at 2.2uF you would be getting a 1st order 237Hz (-3dB) = 61Hz -0.5dB filter
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Use your ears to enjoy music, not as an analyser.

Peef

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Hah, good catch! Very nice time domain response, too.

With the inductor of the third order filter having such a small value I'm almost tempted to build one with a ridiculous air-core inductor...
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MisterRogers

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Ah! yes - apologies; I found that while I was building it for 3rd order, and forgot to pass it on along with the schematic. Great catch.
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MisterRogers

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All,

Finally got back some prices from Lyuben. Here's a snippet from his email to me:

I finally calculated the prices:
1. Non soldered board Euro 4.5
2. SMD soldered board Euro 18
3. Fully soldered board (and tuned if needed) Euro 27

The prices are with paypal fees and without shipping.

He'll eventually get it up on the store, but we can get an order in if there's enough interest. Also, he has a prototype clock daughter board I'll hopefully be building. He's also working on a max performance AK DAC to go with the receiver. I'll post what I know, when I know it. Chime in if you want a Filter board; I send him a count.
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shipsupt

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Was there ever a BOM or more details for the build that started this thread? 
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Yeah, well, you know, that's just, like, your opinion, man.

Hroðulf

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I think I'll wait for the max performance board.
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If it keeps on ringin', levee's goin' to break..

MisterRogers

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No, not really, but I'm happy to provide what's needed. Each of the components that make up this DAC have their own BOM (except for the USB Receiver/DAC), and the build's are fairly standard with the usual tweaks to match impedance, etc.

If anyone is serious about the build (I know one or two of you have already built DAC's with these components), I'm happy to share specifics of my component BOM's. I have a prototype oscillator board inbound, along with evaluation boards for the newer AK4490 & AK4495. I'll share what I learn.

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mvwvm

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What I'd really like to see in the upcoming AK4490 board is the ability to drive an external output stage directly from the (balanced) chip output, bypassing the on-board output stage / BAL-SE converter (ideally it should be possible to order a board with all that stuff left unpopulated). Support for dual mono would also be nice.
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MisterRogers

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So since my last post, we've been through quite a few prototypes and completed the design work for a 4490/4495 DAC. With this one, you can tap balanced out, and it's designed to work stereo & dual mono. Hoping to see final boards this month.
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