The AD-20 from Denecke is a high-quality, two channel, battery operated microphone preamp coupled with a low noise, 20-bit analog to digital converter. The S/PDIF outputs are both optical and coaxial and can drive standard consumer DAT machines or computers that accept digital audio.
The main use for the AD-20 is location recording. Most low cost DAT machines have noisy front ends and a good preamp with a higher bit converter can improve the signal-to-noise ratio by up to 15dB.