BurrBrown PCM63P Stereo Audio DAC
This project is a realization of a long lasting dream that has been in my head since the day 1 into audio electronics. The cost of the atual DA-converter IC's and there was no
really need of a device like this held me back. But when the last electronics store in Stockholm closed down this winter, I was able to source eight BurrBrown PCM63P DAC IC's
for a very good price (among several other items). So, the heart of the build was in my hands. The brain and the guts was still missing...
After some searching through the Internet, I found a good idea to start from. To build a DAC you will need three major parts: the SPDIF-receiver, the Digital filter and the
Digital-Analog converter. Of course, you will need some support systems also like power and control. One thing that was little bit tricky was the age of the design. Today,
parallell DAC's are almost extinguished in favour for serial DAC's. Also, digital receivers for 16-bit are also a part of the history. But, thanks to eBay and DigiKey, I was
able to bring the line together: Crystal CS8412 digital receiver, BurrBrown DF1704 digital filter and of course, the BurrBrown PCM63P 20-bit DAC.
Some additional logic was also needed and I added a digital input switch that makes it possible to switch between optical and electrical input. The power supply is splitted
in two individual sections, one for the digital part and one for the analog. Both sides runs on +5.0 V and -5.0 V. The ground is also splitted with a single connection point
at the rectifier section. All control signals for the digital receiver and the filter have been routed to pinheaders/strapfields at the PCB. This makes it possible to set the
configuration with straps (for stand alone operation) or connect the unit to a microcontroller.
This project is still ongoing - the first unit (I'm going to make totally four of them as I got eight PCM63P) have just played music. And that was some sweet music - the DAC
works like a charm when the strappings are correct...
What still remains in this project is to finish all four units, put one of them in a case (the one I will keep) and sell the rest. I also need to solve a "bug" in the optical
part of the design. I hope a simple fix with two resistors will do the trick. The reason for this is that I'm using a differential driver as a switching element. The coaxial
input is transformer connected, making it a differential input. The TORX-receiver module outputs a TTL-level signal that is single ended. That did not work with the driver IC.
By level-shifting with two resistors, I hope to solve the problem.
2008-06-04: The "bug" with the optical input has been solved. The solution was to add a voltage divider to pin 7 at IC10 (the DS34C86TM). This put the negative diff-input to
about 0.9 V, solving the level problem. So, here is the final, 100% working, schematics and PCB files (for Protel DXP 2004):
Still to do: Finish all four units, write some instructions for the strapping/usage and put up "build guides" (component layout as pdf, bill of material) in case You want to
make your own.
Finally, the pics...