by Marc Heijligers
My interest in DAC design started when attending a demonstration of Audio Innovations and Audio Note audio equipment, in the summer of 1994. In-between the CD player (a TEAC VDRS-10) and the amplifier (a self-made 300B-SE), a strange black box was playing, labeled Audio Note DAC-3. Because there were some problems in the setup, the Audio Note DAC-3 was disconnected, and the amp was connected directly to the VDRS-10. Gone were the involvement, the excitement, and the emotional impact of the music.
Strange, because as an electrical engineer I assumed that a flat response from 20Hz to 20kHz was sufficient for a CD player to sound the same as all others. Wrong. After listening to many CD-players and DACs at that time, I discovered a lot of substantial audible differences between CD-players or DACs, despite the similarity between those obvious frequency-amplitude graphs. Subjective comparison showed differences in treble (less harsh, better transients, more characteristic, cleaner), 3D image (explicit notion of characteristics of the recording location, such as reverberation and pin-pointing of sound sources), harmonics (a voice with more body, instruments like violin and guitar including resonance originating from their cabinet and not only pronouncing the metallic sound or attack of their strings), and dynamics (small-scale details together with large-scale undistorted volume peaks). A good digital source sounds more sophisticated (less forward or stressed), but simultaneously has more spirit (live performance, involvement, emotion), which seems to be contradictory at first sight. For me, these were substantial differences, and hence I wanted to have a DAC too.
Besides wanting to have such a kind of improvement in my audio system, there was a slight problem of not wanting to spend thousands and thousands of dollars. Suddenly a little voice inside my head was telling me: "Hey, you have a master degree in electrical engineering! Why not build such a thing yourself".
So this was the point in time where DIY DAC design came into my mind, and where this DAC project started. The DAC project was distributing itself fast, so within a couple of weeks (October 1994) there was a group of about 4 people who were interested in building a DAC. What we certainly didnt know at that moment was that this project would last to the end of 2000, with about 25 people interested in our DAC.
We didnt have any technical backgrounds w.r.t. DAC design initially. Finding theoretical articles is no problem at all, but finding information about implementation issues is difficult. We did consult our University library, the Internet rec.audio groups and some experts quite often. This gave us at least some insight about which design parameters w.r.t. DAC designing would be interesting to have a look at. But for a large part we relied on basic engineering, experiments and measurements.
Initially I was triggered by a nice DAC design published on the Internet by Sheldon Stokes. Norman Tracy offered another interesting concept. Some of the concepts used in these designs (no analogue filtering, sample rate conversions) were not our ideas (ofcourse), so we started our own design.
Because we werent looking for just yet-another-technical-solution to a well-defined implementation problem, and hence because a good enjoyable sound was given top priority, our design decisions have mainly been guided by extensive (sometimes blind) listening sessions. This implies that lots of design decisions are subjective in nature, which to our opinion is an advantage instead of a disadvantage. It is very difficult to translate ones preference into technical quantities or technical solutions. So, finding a good balances between well-known technical properties of electronics, and a correlation with our perceptive observations (and preference) have been the most creative part of this project. Although we havent found answers to all questions, the final result is - in our opinion - a very nice DAC! Direct comparison with the Audio Note DAC-3 (which started all of this) reveals that our final product sounds at least an order of magnitude better in almost all aspects (confirmed by at least 2 AN-DAC 3 owners). Our DAC has gained a lot of appreciation by many people, resulting in an initial batch of 25 samples.
Jos van Eijndhoven