Owner’s Reference
DirectStream DAC MK2
©2022 PS Audio Inc. All rights reserved.
Introduction
®
PS Audio® Inc. 800-PSAUDIO 4865 Sterling Drive Boulder, Colorado 80301
120dB S/N ratio from 10Hz to 220MHz and have a number of design challenges and problems
associated with even the best designs.
If the analog processing isn’t linear and doesn’t have a very wide bandwidth, it will modulate
the high frequency noise that’s inherent in DSD back into the audio band. That modulation
will not result in just low level noise. In practice it will be aliased back into the audible band
with serious sonic consequences. To maintain low noise and linearity, the design incorporates
both high speed symmetrical video amps and a passive output filter. The first challenge in
such a design is the output switch that generates the final 1’s and 0’s of the modulator.
A very clean switch that hooks up the positive rail with a 1 and the negative rail with a 0 is
essential. If it has too much resistance, if the resistance is different at the positive end than
the negative end, if the resistance changes from time to time, … the result will not be as
clean as it needs to be. For 120dB S/N the switch resistance has to be quite consistent.
Another design requirement is consistent and fast switching time.
If the switch is too slow it won’t keep up with the 5.6MHz signal used in this instrument. If the
switch doesn’t react in consistent times it will introduce jitter. Use of traditional CMOS gates
adds a lot of jitter as do cross-coupled totem-poled bipolar transistors. Instead, DirectStream
MK2 relies on high speed differential video amps, which are essentially class A switches, have
their outputs either near the top rail or near the bottom power supply rail (without ever
saturating) and provide a very clean DSD switch.
For the all important low pass filtering requirements an active filter adds self noise even if it
is effectively lowering incoming noise. A unique and effective solution to this problem is a
passive filter. The design uses a carefully crafted high bandwidth audio transformer at the
output of the instrument for both galvanic isolation from the outside world as well as low
pass filtering.
The PerfectWave DirectStream MK2 DAC represents a significant departure in the design
and execution of PS Audio’s products. We believe this new instrument will help further our
industry, music and the faithful reproduction of music around the world
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