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Old 1st August 2004, 04:29 PM   #1
nl is offline nl  United States
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Default PCM2707 USB-->I2S how to use etc.

Okay, I did a search of the archives and didn't come up with a lot of definitive answers to this:


It seems like the USB input has a lot of advantages, primarily because it is asynchronus, easy to reclock and has error correction. Plus, I have an iBook nearby with iTunes. I'd like to use the PCM2707 or similar as an input, with a Tent clock or similar at the DAC side, and feed a TDA1541 with an I2S signal.

The datasheet has a sample schematic, which helps, but I thought I would see if anyone has done this and has a working circuit.

The datasheet calls for a 12Mhz clock, would a Tent 12.280 Mhz clock work?

The PCM2707+powersupply+clock+clock PS combo seems like it would be a good PCB candidate.
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Old 1st August 2004, 06:39 PM   #2
Nisbeth is offline Nisbeth  Denmark
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No I2S for output and reclocking, but take a look at this: http://www.mellowparenting.demon.co....er/usbdac.html

If you run it off a pair of NiMH-cells and use good components as specified, this plays very nicely. Integrate it with a small headphoneamplifier in a nice case and you have the perfect travelling companion for your iBook


/U.
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Old 1st August 2004, 11:01 PM   #3
nl is offline nl  United States
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Default not 2707

Well, that's OK, but I don't want to use the 2702, I want to use the 2707 (2704-2707), and I want I2S output to drive the TDA1541. I don't want a portable DAC, I want something for my big fat home rig, and I won't use wimpy NiMh cells, because I have stacks of SLA batteries around. This circuit does have a clock, however, so I guess we're making progress.
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Old 2nd August 2004, 07:57 PM   #4
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Default it works! do it!

hey nl. I did exactly (I think anyway) what you want to try. I worked off the TI data sheet for the 2707 and improvised where necessary. All components are surface mount except for big filter caps and mounted as close to the 2707 as I could get. If you put a switch on the FSEL line you can switch between piping the I2S to the internal DAC or an external DAC chip of your choice. Make sure you do NOT power the beastie off the USB bus, build yourself a nice well filtered low impedance supply dedicated to the DAC.

How's it sound? absolutely the BEST I have heard in my system (homebrew Class A 6C33C tube amp, passive pre, driving highly modified ADS speaks). Here's what blows my mind: I built up a simple TDA1543 DAC with passive IV conversion and did a comparison with the internal DAC. INSTANT preference, no subltlety to it AT ALL...the internal DAC (yeah yeah I know, oversampling and all!!!) sounded WAY more natural than the 1543. That's what I use full time now. The things that are important to me (good frequency extension, good microdetail, good sound staging) are THERE. The 1543 sounds more or less like everything else I have tried.

just my 2 cents. Happy to supply more circuit detail if you like.

cheers
Adam Reed
Ashland Oregon
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Old 5th August 2005, 12:29 PM   #5
Radian is offline Radian  Germany
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Default Internal dac

Hi Adam,

Very interesting!

I did the same PCM2706 but with external TDA1543, very good but if internal dac is still better, wow!
Could you please post schematic?

Klaus
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