I purchased an Audio Alchemy DDE 1.0 on the diyaudio forums
for a very reasonable price. Audio Alchemy had a stellar reputation in the 1990's for producing high-quality gear that
was inexpensive compared to standard "audiophile" gear. I believe the principal designer founded Perpetual Technologies
after Audio Alchemy went belly-up.
For this project, I did pretty simple mods. My goal was to update the parts of the DAC that were
deficient and/or would need eventual replacing. The first thing to go were the RCA jacks. They were already in bad shape
when I purchased the DAC -- the gold flash finish had all but worn off, and corrosion was forming.
Audio Alchemy did a great job bypassing all the caps in the DDE 1.0 with Metallized Polypropylene
caps. However, their Electrolytic caps appeared to be your standard generic no-name brands. I went ahead and swapped all
the electrolytics with Panasonic FM caps. I added additional capacitence in front and immediately after all the voltage
regulators by putting in the largest caps of the same voltage rating that would fit. I used Nichicon Muse caps in the spots
where I couldn't find a Panasonic FM capacitor in that value (usually under 10uF).
The final bit of upgrading was done by replacing the 78xx/79xx 3 terminal regulators with the best
"modern" equivelents I could find. These were generally spec'd by looking at the datasheets for the various brands on
Digikey and figuring out which had the best ripple rejection and lowest noise. I also desoldered the Analog Devices AD797
Op amp and put in an 8-pin DIP socket so that op-amp rolling could be performed if needed (which it wasn't, the AD797 is a
pretty dang good op-amp).
Here's the images of the DAC:
