HQ USB to SPDIF Circuit Design??? - diyAudio
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Old 26th June 2005, 03:02 PM   #1
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Default HQ USB to SPDIF Circuit Design???

Hello:

Does anyone know of a source for a HQ circuit design
to go from computer USB to true SPDIF output? Also,
how would playback of hard drive wav music files be
controlled with a windows based computer?

Thanks in advance!

Fastcat
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Old 27th June 2005, 10:46 PM   #2
kostix is offline kostix  Mexico
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Hello there!

There are several chips which do just that.
One example is Texas Instrument/Burrbrown's PCM2906 - very nice device.

Its a USB audio codec, including stereo analog in and out, aswell as SPDIF in and out.

http://focus.ti.com/docs/prod/folder...t/pcm2906.html


I've designed a PCB for it, which gives pretty nice performance
Its based on the circuit straight from the datasheet.
Its dead silent,- i tested it on professional studio powered monitors, and with the volume all the way up, there was 0 noise.

I have spent a considerable time on getting it that way, and came to the conclusion that the key for this, is to NOT to connect the analog audio in and out GROUNDS with the rest of the systems grounds at all. This way u have a "floating" ground, where the analog IN/OUT grounds, get their GND path thru the device to which you are connecting this circuit, ie. an amplifier, mixing desk, mic preamp, etc, and this way the fast speed digital gnds dont introduce noise into the sensitive audio signal.

I've used normal size resistors and capacitors as its a bit difficult to get them surface mount here, but I am pretty sure that the performance will be far better if SMT passives are used.

Also, when I built this device, I also built the little enclosure from wood, and I had to screen all of the enclosures walls, with sheets of metal, interconnect them electrically and ground them.
Without the screen a lot of noise was introduced in the analog input section, with the screening it was reduced considerably.

Ok thats it.
I hope it will help you anyhow in whatever you are trying to achieve.

Good luck!
Attached Files
File Type: zip pcm2906 usb soundcard.zip (75.4 KB, 307 views)
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Old 28th June 2005, 01:32 AM   #3
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Hello and thanks for the SPDIF/USB info!

I cannot make any sense of the zip file that you
attached. Dont know how to open the unziped
files in it. Any suggestions?

Also, what software did you use with a PC to
operate playback through the USB/SPDIF?

Thanks!

Fastcat
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Old 28th June 2005, 02:10 AM   #4
kostix is offline kostix  Mexico
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The zipped files open with a program called Eagle. Its used for designing schematics and from there printed circuit boards.
www.cadsoft.de


About playback, when you connect this chip to the USB of the PC, it is recognized automatically by windows (pc, mac or linux) as a USB Audio Device, and you can use this driver in any sound application.
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Old 30th June 2005, 03:58 PM   #5
verdonc is offline verdonc  Belgium
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Schematic request please. The evaluation version of Eagle doesn't work well. Could a .pdf be posted?
Thanks!
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Old 30th June 2005, 04:45 PM   #6
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Quote:
Originally posted by verdonc
Schematic request please. The evaluation version of Eagle doesn't work well. Could a .pdf be posted?
Thanks!

verdonc,
you find a complete schematic, included spdif in/out in the pcm2902 evaluation board page (see user guide):

DEM-PCM2902
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Old 30th June 2005, 08:33 PM   #7
kostix is offline kostix  Mexico
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http://www-s.ti.com/sc/ds/pcm2906.pdf

this is the datasheet for the chip itself...

all the needed stuff is there. there is a schematic for the whole thing.
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Old 3rd July 2005, 12:02 PM   #8
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I have build a USB-S/Pdif interface for my minidisk player based on a BB PCM2902. You can sample it for free and it only requires a few external components (crystal, resistors, caps). It also has an analog output stage but i wasn't so pleased with it.
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Old 4th July 2005, 10:52 AM   #9
guzzler is offline guzzler  Scotland
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http://ecp.cc/usb-spdif.html

I've still got a few boards left over if you're interested

g
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Old 4th July 2005, 06:00 PM   #10
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Nice little circuit Kostix. I was just wondering how you mounted the components? Any chance of a pic?
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