At the present time my source is a Conrad Johnson D/A-2b. I've reprinted CJ's description and design theory on it because apparently it must be right. I find this DAC to be more musically correct than anything else I've owned or heard between $800 ~ $8000. With the speed and transparency of our Zen Triode amplifiers this is also the leader in accuracy of sound stage and focus.
Reprinted from their website:
The D/A-2b and D/A-3 Digital Processors
A digital processor accepts the data stream from the transport and converts the numerical data back into music. Several circuits are involved in this process. Of these, data conversion, analogue filtering and power supplies are particularly important to faithful music reproduction.
We have chosen to use bit-stream DAC chips for these processors because we find that they offer by far the most musical performance. The edgy, unmusical sound that we typically find with multi-bit DACs is probably attributable to a type of crossover-notch distortion which is intrinsic to these designs, and absent from bit-stream converters. This distortion is essentially invariant to signal amplitude, making it most noticeable on delicate musical passages, obscuring ambience information, tonal nuance, and harmonic subtlety The bit-stream approach reproduces these important elements of musical information far more naturally
The final stage of any DAC is the analogue output stage. This stage is a low-pass filter, designed to remove high-frequency (supersonic) artifacts of the conversion process. In the majority of units presently on the market, this critical function is performed by an IC op-amp, with much the same result as would be expected from using that device in a preamplifier. In contrast, the output stages of the D/A-2b and D/A-3 are designed and executed in much the same way as our preamplifier circuits, using discrete devices - the D/A-2b using vacuum-tubes, the D/A-3 using field-effect transistors.
Always important, power supply des critical to the musical performance of a tal processor, because of the need to isolate the sensitive analogue audio stages from the very high-frequency noise generated in the digital sections. In the D/A-2b and the D/A-3, dc voltage is supplied to the audio stage by a discrete regulated power supply, designed to offer vanishingly low impedance at all audio frequencies. These power supplies use polypropylene and polystyrene capacitors exclusively A similar, separate regulator supplies DC to the analogue circuits in the DAC chip - the origin of the audio signal.
The DR-1, D/A-2b and D/A-3 have been designed and produced with care to transform digital sources into a musically rewarding experience. These digital playback systems offer depth and focus of soundstage, tonal accuracy, and an ability to convey nuance in musical performances that many audiophiles have felt would not be possible from compact disc.