Peter Daniel (whose company is AudioSector, based in Toronto) sells an S/PDIF as well as a USB version of his non-oversampling (NOS) DAC built around the TDA 1543 chip. More info on his DACs is contained in his links in the "Latest News" section of his webpage.
Like his gainclone amps, Peter has put great effort into the physical layout (small circuit paths) and parts selection for these units. He sells the S/PDIF unit assembled under the AudioSector name, and sells both versions as kits, or just bare PCBs. I bought the PCBs with the chips (Peter mounted the surface mount chips for me, very helpful) and the transformer. I bought the balance of the parts from Michael Percy (Percyaudio.com) and from Digikey.
I built the unit using the parts specified by Peter on his schematic, including a number of Blackgate N (nonpolar) caps and Riken I/V resistors, some of which are now quite difficult to find as they are out of production. Despite a relatively simple circuit, this DAC has completely separate power supplies for the audio and digital circuits, and uses a total of four on-board power supply regulators.
Above: Unstuffed PCB, top view, click to enlarge. Notice the PCB is very nicely done, and is gold plated. The power transformer mounts to the left, rectifiers and filter caps next, then DAC circuitry to the right.
Above: Bottom view of stuffed PCB (not mine, but looks the same), click to enlarge. Notice the USB (type B) jack on the lower left. Also note the TDA1543 8-pin DAC chip near the center, and the surface mount PCM2706 USB interface below that. There is a 12MHz clock next to that chip. Power supply regulators and decoupling caps mount directly above the power pins for each chip on the top of the PCB.
Above: The populated PCB mounted in my chassis, click to enlarge. Note that rectifiers are MSR860 soft recovery TO-220s and the caps are nearly all Blackgates. The red sleeved ones are type N - nonpolars. There is only one OS-Con decoupling the regulator for the clock. The passive I/V resistors are Riken 1% carbon film, most others are Dale 1% metal films. The transformer is an oversized dual 8V unit, 48VA. There are 4 regulators on the PCB, including two for the USB interface, one for the clock, and one for the DAC chip.
Above: Completed unit, click to enlarge. I used a piece of thick aluminum stock for the cover, and added damping material to the chassis at Peter's suggestion. There's a small LED on the front that derives its power from the USB port (none of the DAC circuitry is powered by the PC). The LED lights whenever the connected PC is on, but the DAC is on as long as its plugged in (no on/off switch).
Above: Rear view, click to enlarge. I used Vampire CM2F RCA's.
I first made a simple faceplate from aluminum stock and dry-transfer letters (shown in the photo at the top of this page), and later had the same design fabricated by Frontpanelexpress.com for a more professional look. Once assembled, I let the unit run in for 2 weeks - the Blackgates have a very long burn-in time. I listened periodically during that period, and heard the softer, less defined sound that I've read is typical of Non-Oversampling DACs. However, once burned in, we did a listening comparison between my Audio Research CD2 player and the same music from a MS Windows XP based music server, using Foobar and FLAC encoding. After getting levels set we actually found the two sources nearly indistinguishable, a good thing since the CD2 is quite good.