Frequently Asked Questions

This product is discontinued. This is an archived page.
  1. Asynchronous Reclocking
  2. I2S
  3. Output Stage
  4. Error Correction vs. Jitter
  5. Slaving Computer Soundcards
  6. Battery for Digital Schematics?
  7. Stacking Multiple Converter Chips
  8. Benchmark's UltraLock
  9. Digital Filtering
  10. One-box CD Players
  11. Synchronous Reclocking
  12. Jitter Sources
  13. Large Buffer
  14. Disbelief in LessLoss
  15. A/D Converters
  16. Sampling Rates


How about the analog output stage (I/V conversion and LP filter)? Does it use opamps or is it discrete? Is there an output buffer and what is the output impedance?

LessLoss Reply:

The LessLoss DAC volume control is a discreet shunt resistor type, and as the volume level is turned to minimum, the output impedance lessens to 0 Ohms; however, this is not crucial in this case, because later in the schematic, there is an output buffer, which has a constant (always the same for all volume levels) output impedance.

The I/V conversion is active and uses high quality opamps chosen by ear. The filter is a discrete design of Vil's and is very smooth, due to the oversampling used. The detail and quality of the signal are therefore very clean.

Poorly designed output stages have higher output impedances, this is true. When the output impedance is lower, the line cable has less influence on the sound quality. The DAC 2004 has an output impedence of a few Ohms. To be frank, we have not exactly measured this parameter. It isn't that easy to measure accurately. Please consider the following advantages and disadvantages of discreet transistor replacement for opamps. Be informed that we have tried this solution while developing the DAC 2004.

The pros:

If everything is well executed, the expected results should be a tad better than with opamps. It is possible to optimize the parameters according to what works best at that place in the schematics.


The cons:

One difficulty is that every single transistor must be chosen according to the needed amplification coefficient. There is an unavoidable temperature swing which affects the performance parameters. As this is a battery powered part of the DAC 2004, it was designed to be turned on and off for charging and the temperature stability during operation cannot be completely guaranteed. It becomes absolutely necessary to use capacitors in the signal path in the output. In our current solution we avoid this altogether, which leads to the clarity of the signal very comparable to that present at the very output legs of the converter chips. Through our long battle with Jitter we realized the importance of extremely short and controlled signal paths (all of them) for top performance, and using transistors would necessarily make for a larger circuit, many more components, a more complicated solution at the part where all we really want is the output to be present in pristine form in the cable. There would be many more soldering points up to our solid silver wires going to the conectors. And the worst thing is the caps in the signal path.

We would like to stress that everything possible is done to direct the outputs of the DAC chips directly out of the DAC 2004 unit, while taking all load off of it. It truly is as close to a cable-ending analogue source as possible (a few cm and that's all).

Let me just add that we have since upgraded the automatic battery charger so that a slight trickle charge is given to the batteries when they are low and this way, no automatic shut-off of the sound ever occurs, and you can choose to continue to listen even when the batteries are low and have been running for over 12 hours straight. The LessLoss DAC uses the same power regardless of the music signal (Class A design). No audible difference is perceived when the batteries are freshly charged or quite low (after 12 hours).