Usb Pcm1794 Dac

andrei · 14th April 2006, 10:05 PM

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:

andrei · 14th April 2006, 10:08 PM

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.

hifimaker · 15th April 2006, 03:35 PM

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

dsavitsk · 15th April 2006, 04:29 PM

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

andrei · 16th April 2006, 02:02 AM

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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14th April 2006, 10:08 PM	#2
andrei diyAudio Member Join Date: Dec 2002 Location: Canada	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.

15th April 2006, 03:35 PM	#3
hifimaker diyAudio Member Join Date: Oct 2003 Location: San Jose	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

15th April 2006, 04:29 PM	#4
dsavitsk diyAudio Member Join Date: Jan 2005 Location: Chicago	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

16th April 2006, 02:02 AM	#5
andrei diyAudio Member Join Date: Dec 2002 Location: Canada	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...