These are some pictures of a prototype digital to analog converter still sitting on breadboard. The design is modular, using a common receiver, asynchronous upsampler, and discreet output buffer, but with the option to use different DAC and I/V modules. Shown below, the prototype module is based on the Burr-Brown PCM1798 DAC utilizing a current steering "Common Base" I to V converter.
The circuit (both the I/V and the output buffer) does not use any feedback. Further, the design is fully differential and does not use any capacitors in the signal path. And, as with all of out designs, the output is transformer coupled allowing for easy full-signal connection to balanced or single ended amplifiers.
We are working on DAC modules for several popular DAC chips, including the Burr-Brown PCM1794 and PCM1798, Wolfson WM8741, Analog AD1955, and several others.
Also shown below are some initial measurements of both THD (0.001%) and IMD (0.006%).
An ETA for a production DAC has not been determined, but we are hopeful it is not too far off.
Walnut Prototype
Walnut Prototype Total Harmonc Distortion
Walnut Prototype Intermodulation Distortion