NOS-USB-DAC Prototypers wanted
Mar 20, 2006 at 3:45 AM Thread Starter Post #1 of 4

dsavitsk

MOT: ECP Audio
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I am looking for help with prototyping a TDA1543 based Non Oversampling USB DAC. It is based on the design I have done before (http://www.ecp.cc/NOS-USB-DAC.html) but has some layout and schematic improvements. The project is envisioned as a reasonably high quality USB DAC for under $75, maybe even under $60 (+ case, connectors, etc, but the power supplies are included.) Maxing out the board with Blackgates, Riken I/V resistors, etc. probably adds another $25. It is AC powered and will work with both 115 and 230V -- there are jumpers to put the transformer primaries in series or parallel.

Ideal prototypers will have some experience with TDA1543 based DAC's as well as with other USB DACs (so you can compare) and with soldering surface mount components (there are about 32 0805 parts + the PCM2707.) Further, you should have, or have access to, a TDA1543 chip and you should be willing to build this sooner than later (I may have some extra chips.) Oh, someone in a 230V country would be appreciated to make sure the board works with higher voltages and that appropriate parts can be found easily.

The cost to build the prototype will be $22 (plus shipping) for a board, output caps, and I/V resistors from me. Other parts can be obtained from Digikey and will run around $40 (the parts list on my website is mostly correct -- I'll give you an updated list.) Also, please note that this is a prototype so there is some risk that it won't work at all -- though it is based on the last one I built so I think things should go smoothly. Production boards will have soldermask and silkscreen, etc. (though the prototype boards will not) so the warnings on the website don't apply.

The number of prototype boards will be very limited, but, if all goes well, and if there is sufficient interest, I will hopefully do a limited run of boards in the near future. Price is anticipated to be in the $12-13 range for a board, and hopefully under $18 for a board + output caps + I/V resistors + single TDA1543 chip (the rest of the parts being available from Digikey.)

Anyway, if you are interested in prototyping, please send me a PM. Also, if you are just interested in the project, you can email me at usb_boards@ecp.cc. Whether or not the project goes through depends upon whether there is sufficient interest. Time frame is unknown, but once all clearance is made through Head-Fi, this will hopefully be sooner than later, but we'll see. If everything goes well and there is interest, keep your eye out for a Mall-Fi ad in the near future.

Board size is 3.5" x 2.8" (96.52mm x 63.5mm)-- small enough to fit in a case with your amp
smily_headphones1.gif


The current board looks like this, but I am very open to comments, concerns, or suggestions for changes. I appreciate any help. Thanks.

NOSUSBDAC0.4a2.GIF



-d
 
Mar 20, 2006 at 10:26 PM Post #3 of 4

dsavitsk

MOT: ECP Audio
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Oh, a couple of notes about the power supply I forgot to mention.

Yes, placing a transformer this close to the circuitry does induce some noise. It is a tradeoff for such a small board. However, if you don't need it quite so small, you can put terminal blocks in the transformer pads and wire the transformer off board. This does help and is a decent solution. You could even use 2 boards, one for the PS circuitry and the other for the DAC which would provide good isolation.

Another advantage to using the transformer off board is that you can use a larger transformer and supply enough current to stack a bunch of chips if that is your preference. If you do this, you could leave out R4 and wire an 8V DC fan there instead.

You can also power the board via DC. To do this, you would simply not populate C1, C2, C3, C4, C5, C19-C26, D1-D8, L1, R1, R2, R3, and the transformer. You would need to supply about 12V DC to the pads of C5, and anywhere from 7V to 12V DC to the pads of C4. The benefit here is that it avoids any high voltage and probably reduces the noise a bit more. It also lowers the build cost by about $20-$25. If you are feeling really cheap, you could even leave out U4 and C8 and supply more like 5V to output pad of U4 (U4 is a LM7805).

-d
 

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