[dsavitsk]

Does anyone here have a sense how difficult it would be to design a PCB to use a PCM2902 to go from USB to s/pdif? I have built one of the guzzler usb dac's (which I love, b/t/w) but I am really in need for a digital out. Anyone interested in this as a project? I'd prefer to power it from USB as this would make it an easy add on for existing DACs

If a PCB could be designed and produced for not too much money, I'd be interested in being in charge of having them made and distributing them.

-d

 

[Nisbeth]

Sounds interesting. Elektor published a design using the PCM2902 some time ago (issue 12/2002) and I've considered buying a PCB for it, but I'm sure the design can be improved.

/U.

EDIT: I'm not sure how far along 00940 is with his project of combining the PCM2704 and the PCM1794 for a "reference" USB-DAC, but maybe that would be interesting as well?

 

[00940]

I could design quickly a small pcb for the PCM2902. Should be rather easy. It would probably be nice to design it to fit easily into the smallest hammond.

Nisbeth : I sadly lost the *.brd files for the pcm2707/ad1896/pcm1794 dac, so I'm starting again from scratch. I'm trying to make it a bit easier to case. Anyway, I really think a small usb-spdif adapter could be useful.

 

[Nisbeth]

Quote:

Originally Posted by 00940 I could design quickly a small pcb for the PCM2902. Should be rather easy. It would probably be nice to design it to fit easily into the smallest hammond.

That would be great. I would prefer something with both inputs and outputs

Quote:

Originally Posted by 00940 Nisbeth : I sadly lost the *.brd files for the pcm2707/ad1896/pcm1794 dac, so I'm starting again from scratch.

Sorry to hear that. If/when you make a new design, please keep us informed

/U.

 

[dsavitsk]

Quote:

Originally Posted by 00940 I could design quickly a small pcb for the PCM2902. Should be rather easy. It would probably be nice to design it to fit easily into the smallest hammond. Nisbeth : I sadly lost the *.brd files for the pcm2707/ad1896/pcm1794 dac, so I'm starting again from scratch. I'm trying to make it a bit easier to case. Anyway, I really think a small usb-spdif adapter could be useful.

The smaller, the better. In addition to sizing for a hammond, perhape there are some "L" shaped screws we could find such that it could easily be panel mounted with just a hole cut out for the USB jack? I found panel mount USB type B adapters, but they are about $10 per, which seems too high.

 

[00940]

Quote:

Originally Posted by Nisbeth That would be great. I would prefer something with both inputs and outputs

inputs : usb/analog/spdif
outputs : analog/spdif

I'm not sure the quality of the pcm2902 justifies a digital input and is A to D conversion really useful ? I would rather offer optical and coaxial outputs.

I had a first look at the datasheet.

As always, the problem is to feed it with a decent power supply. Seems like the device operates well from 4,35V to 5,25V (graphs are flat actually). It would be easy to just use a reg101-a configured for roughly 4.5V, with a lpf before it to cut the noise coming from the usb supply, just as on the USB dac rev. A. The 0.4V are allowing for some fluctuation of the usb supply from a computer to another.

 

[dsavitsk]

Quote:

Originally Posted by Nisbeth That would be great. I would prefer something with both inputs and outputs

If it were to have both in and out, I'd prefer to be able to simply not populate the in portion. USB seems finicky enough that I am not sure I would trust the in enough to use it.

-d

 

[dsavitsk]

Quote:

Originally Posted by 00940 I would rather offer optical and coaxial outputs.

The coax is particularly useful as it would be easy to build an internal switch into an existing dac. Also, Xitel has a cheap usb->optical (the DG2) that can be picked up on ebay for about $25 U.S. making this less of a needed item.

 

[Nisbeth]

Quote:

Originally Posted by dsavitsk If it were to have both in and out, I'd prefer to be able to simply not populate the in portion. USB seems finicky enough that I am not sure I would trust the in enough to use it. -d

I just reread the datasheet and you're probably right - inputs aren't worth it.


/U.

 

[00940]

Hum, what then ? A minijack for analog out and a rca for coax ? Or is optical really needed ? Advantage of coax is that it simplifies the layout

 

[dsavitsk]

Quote:

Originally Posted by 00940 Hum, what then ? A minijack for analog out and a rca for coax ? Or is optical really needed ? Advantage of coax is that it simplifies the layout

That could work, though if it reduces the number of components, my need is just straight usb -> coax. I've got plenty of analog out converters, I just need to get them a signal

 

[Garbz]

I'm not sure how the USB dac work because I haven't been following it. But if it shares GND with the computer then I suggest offer optical as well. Call me paranoid but I'd rather put up with the slightly higher jitter of toslink adapters then contaminate the DAC on the otherside.

 

[00940]

hum, a little problem, I'll update that later on.

 

[Nisbeth]

Looks good!

/U.

 

[00940]

Ok. Here's a digital only version. It has a better (buffered) coaxial output, using a 74HC04. To be short, the TTL output goes into a first buffer, is tapped afterwards for the TOTX, goes into a pair of paralled buffer and then is finally sent to the RCA.

Everything is powered from usb bus of course, the 74HC04 and the optical transmitter have their regulators. Following the evaluation board, I just put everything on a groundplane.

estimated cost at roughly 40$, including enclosure but without pcb. If you put everything on it of course.