|Developed front||Developed rev.||Etching||Etched|
This is an external DAC that I made to connect my PC to hi-fi stereo amp. Analog connection would be too long, about 8 meters of wire, so I decided that an external DAC is a necessity. This page is also mainly a description of PCB-making process. Some stages, like making the vias, are not pictured. This is not work-in-progress anymore, although there are no newer pictures available.
The DAC is using a CS8416 as SPDIF->I2S receiver and AD1955 for DAC. Output filters are copied from AD1955 datasheet. The outputs are single-ended, compatible to consumer stereo equipment. The chips are controlled by ATmega8L microcontroller. The latter also provides an extensive debugging interface which allows editing of all receiver and DAC registers.
I don't have equipment to measure quality of the achieved result. Subjective testing shows that it is definitely worse than Micromega Minium CD source. But, although sound degradation can be heard, it must be taken into account that digital feed is provided from a PC that does 44.1kSPS->48kSPS conversion. Another test was conducted with a BBK DVD player, but due to limited availability of the source device this test was limited and I could not make any decisions regarding possible resampling. Sound was comparable, without a clear winner.
If I was doing this same project today, I would definitely change several things and here they are: 1) Put local voltage regulators on the main board. 2) Probably ditch the uC: it's priceless for debugging, but not useful after everything is set up. 3) Recalculate the filters to be much higher than audible frequency. Micromega datasheet says that their output filters are set to 75kHz above audible range.
See the circuit (PDF). I remember that there were some minor fixes in the process, but I wasn't updating the schematic because there was nothing really dramatic, only some tweaks.
This archive contains the entire Eagle project that you can use to build your own DAC without
using brain wasting too much time. Here you can find the source code.
The sources are also available on github: [sources], [hardware].
Feel free to contact me if you want PCB layouts and firmware. The name is svofski and gm@il is .com.