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Old 27th May 2005, 09:52 PM   #1
pixpop is offline pixpop  United States
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Default Ugliest DAC.. but tiny!

Just finished this silly project. It's a PCM2902, bus powered with no analog buffer. The wiring is straight from the 2902 datasheet.

It's about the size of a matchbox.

Surprised the heck out of me when I plugged it in, and it worked. No noise or hum problems, but the sound is so so. Quite poor bass for some reason, though the highs are fine. The output coupling caps are 10uF.

I wonder how much better it could sound if the power was done right.

Click the image to open in full size.
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Old 27th May 2005, 10:11 PM   #2
tool49 is offline tool49  Canada
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Interesting!

I made a bigger (about the size of two business cards side by side) version of the PCM2902. It outputs in a OPA2134 and the sound is quite good. I noticed a tremendous improvement when I added the REG103 as suggested in the suggested schematic of page 27.

I also built a wall powered unit (kind of defeats the point of USB but...) and the sound quality is leaps and bound better. Actually it is my reference when I build new gear now. The improvement is all around but it is especially present when driving harder loads (i.e. headphones).

Congratulations on the tiny design (I wish I could pack as much punch per cubic inches in my designs!)
Sébastien
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Old 27th May 2005, 10:37 PM   #3
gmarsh is offline gmarsh  Canada
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beautiful hack... especially the SMT tantalum output capacitors hanging in the air
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Old 27th May 2005, 11:02 PM   #4
jleaman is offline jleaman  Belgium
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post schematic ? id like to make a usb dac for my laptop.. Please. post schematic..

J'
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Old 27th May 2005, 11:28 PM   #5
tool49 is offline tool49  Canada
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Jleaman:
Quote:
The wiring is straight from the 2902 datasheet.
I don't mean to be rude, but the schematic is in the datasheet

Sébastien
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Old 27th May 2005, 11:30 PM   #6
jleaman is offline jleaman  Belgium
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Sorry can you post a link to that pdf then please ?
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Old 27th May 2005, 11:42 PM   #7
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Default Re: Ugliest DAC.. but tiny!

Quote:
Originally posted by pixpop
Just finished this silly project. It's a PCM2902, bus powered with no analog buffer. The wiring is straight from the 2902 datasheet.

It's about the size of a matchbox.

Surprised the heck out of me when I plugged it in, and it worked. No noise or hum problems, but the sound is so so. Quite poor bass for some reason, though the highs are fine. The output coupling caps are 10uF.

I wonder how much better it could sound if the power was done right.

Click the image to open in full size.

Very nice pixpop!

I made something similar:

Click the image to open in full size.
(click to enlarge)


Only PCB:

Click the image to open in full size.
(click to enlarge)

Using an output buffer the sound is very good, also on basses. I used for input and output buffers the Burr-Brown OPA2353, that work with the 5V from USB.
Output coupling with bipolar 47 uF.

@ jleaman: just go to www.ti.com and search for PCM2902
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Old 27th May 2005, 11:50 PM   #8
jleaman is offline jleaman  Belgium
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Default Re: Re: Ugliest DAC.. but tiny!

Quote:
Originally posted by paologatto



Very nice pixpop!

I made something similar:

Click the image to open in full size.
(click to enlarge)


Only PCB:

Click the image to open in full size.
(click to enlarge)

Using an output buffer the sound is very good, also on basses. I used for input and output buffers the Burr-Brown OPA2353, that work with the 5V from USB.
Output coupling with bipolar 47 uF.

@ jleaman: just go to www.ti.com and search for PCM2902


ANy boards left ? id buy one..
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Old 28th May 2005, 01:14 AM   #9
pixpop is offline pixpop  United States
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I have another 2902 chip. Perhaps I'll build a better one, now that I've seen how easy it is. If I build another one, I'll connect all the inputs and outputs, not just the analog out as I did in this one.

Still, an M-Audio Transit is only $99.00
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Old 28th May 2005, 01:15 AM   #10
jleaman is offline jleaman  Belgium
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Quote:
Originally posted by pixpop
I have another 2902 chip. Perhaps I'll build a better one, now that I've seen how easy it is. If I build another one, I'll connect all the inputs and outputs, not just the analog out as I did in this one.

Still, an M-Audio Transit is only $99.00
My point DIY Do It Your Self that is why i asked for the board.. I wonder if i could buy one if not i should be able to find a schematic and design my own board..
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