From Soekris:

1421 is our high performance single-ended DAC with built-in powerful headphone amplifier. 1421 is based on the well-tested and renowned Soekris R-2R technology. The dac1421 has the same features, performance, and quality as the top end dac1541, just without the balanced signal chain. It has the fantastically clean and natural sound of a 27 bit R-2R sign-magnitude DAC, built with over two hundred tiny and ultra precise thin film resistors. The line output buffer is a high-performance, fully-balanced, zero-feedback design built with discrete parts. The buffer also has a high power mode to drive any set of headphones.

The main power supplies are ultra low noise, low impedance, very fast, and are also built with discrete parts. The music is delivered over an USB interface in both PCM and DSD formats, or by the SPDIF, AES or Toslink inputs. It is then buffered and re-clocked using a precise and ultra low jitter oscillator. The digital processing is done in a programmable FPGA chip, with a set of select-able advanced digital filters and a digital volume control.

Please visit the official Soekris page below for more info, specifications, drivers, and manual.

http://www.soekris.dk/dac1421.html