The Soekris Discrete R-2R Sign Magnitude Technology

The Soekris Digital to Analog Converter (DAC) products are all based on our own advanced discrete R-2R sign magnitude technology, with a large programable logic chip for all the digital processing and a high number of very precise thin film resistors for the digital to analog conversion.

Almost all digital recordings are made using whats called Pulse Code Modulation (PCM) which is that you sample the analog signal at a cetain resolution and at a certain rate, for the CD media that is 16 bit per sample at 44100 samples per second and for newer recordings that are usually 24 bit per sample at up to 384000 samples per second. 16 bit samples represent a number up to +-32767, while 24 bit represent a number up to +-8388608. To convert the digital recording back to analog the optimal way is to convert directly to analog signals using a R-2R converter, which is what you did in the begining when playing digital recordings. But good R-2R chips are expensive to manufacture, and soon the Delta Sigma DAC technology started to catch on, not because it's better, but because it can be manufactured using low cost high volume chip processing, avoiding the costly trimming process needed for multibit DAC chips....

A Delta Sigma DAC take the 16-24 bit samples and convert them to 1 bit samples, later on to 2-5 bit samples, at much higher speed. That creates high levels of noise, but by increasing the number of Delta-Sigma modulators after each other, typical up to five, that noise is moved up in frequency to above what you can hear. Unfortunately those higher order Delta Sigma DACs are in principle unstable and have a number of side effects which the Delta Sigma chip manufactures all try to reduce.... So Delta Sigma DACs all work just fine when feed simple signals, like sinus tones, but run into problems when feed comples signals, like music....

Now we are seing the R-2R DAC return as the sound are just much more natural. Soekris Engineering have developed our own R-2R technology by taking advantage of the falling cost of programmable digital logic chips and the availability of lower cost very precise thin film resistors, and with our boards manufactured in advanced surface mount technology.

There is basically two kinds of R-2R converter chips, one kind using a single R-2R network, like your typical industrial DAC and one kind using dual R-2R network called a Sign Magnitude converter, typically only DACs for Audio use. Digital Audio samples are represented by +- numbers centered around zero. The R-2R network have to be very precise when using a single network as any unlinearity are relative to full signal level. So a R-2R converter specified with 0.001% distortion looks good on paper, but the distortion is relative to full signal level, resulting in increased distortion as the signal level goes down, at - 60 dB signal level the distortion is then 1%....

Here is where the Sign Magnitude technology used by the Soekris DAC comes in, by having dual R-2R networks, one for the positive signals and one for the negative signals. The result is then that the unlinearity are relative to the actual signal level, NOT the full signal levels.... So a Sign Magnitude converter specified at 0.01% distortion with also have 0.01% distortion at the -60 dB level. As music are very dynamic with tiny details that will result in much better and natural sound quality at all levels.

But what about the newer DSD recordings ? DSD is basically that you move the main part of a Delta Sigma converter from the player to to recording process, which still have all the disadvantages of the Delta Sigma processing, and even worse, it's locked to just one bit.... It might improve over the old 16 bit / 44100 samples per second of the CD player, but can't beat a good high resolution PCM recording. We have choosen to support DSD recording as sometimes it is the only available format for a recording. A DSD player is then basically a low pass filtering of the DSD bitstream, and we are doing the DSD to PCM conversion in a perfect digital process so you still can take advantage of our DAC quality and even use our perfect digital volume control.