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Old 14th April 2006, 10:05 PM   #1
andrei is offline andrei  Canada
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Default Usb Pcm1794 Dac

I was thinking about building something small and fun, and figured that USB headphone amplifier will do nicely. Here is what I came up with:
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File Type: pdf usb-dac-pre.pdf (47.5 KB, 380 views)
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Old 14th April 2006, 10:08 PM   #2
andrei is offline andrei  Canada
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Points of interest are passive I/V converter and filter implemented using step-up transformer and no-feedback monolythic buffer to drive the headphones...

Power supplies are not shown.
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Old 15th April 2006, 03:35 PM   #3
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Hi Andrei,

Pretty cool, I was also thinking of designing a DAC with TI's USB and DAC chips.

Have you considered having a balanced outputs to a preamp plus a headphone out?

I'd like to design a similar circuit with the Pass D1 I/V stage in balanced mode. One nice aspect of the Pass I/V is the way Neson incorporated a volume control.

-David
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Old 15th April 2006, 04:29 PM   #4
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Very neat. I would add a few things: You should put a volume pot before the intersil buffers. Digital attenuation via the computer degrades sound quality. Second, those buffers have a tendancy toward dc offset without a 1K resistor on the input. I am working on a similar thing but with a tda1543 and all usb power: http://headwize.com/ubb/showpage.php?fnum=3&tid=6233

-d
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Old 16th April 2006, 02:02 AM   #5
andrei is offline andrei  Canada
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This one is also bus-powered. -5V supply is generated onboard by a LT1931A switcher. I am trying to get it into a very small PCB footprint - 2x8cm or so - so I dropped a few extras...
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