Digital Link III DAC

While everyone is talking about multi-channel audio, Blue Ray, High Def this and high Def that, the truth is 99% of our customers still have huge CD collections that would benefit from the finest of players and DAC’s.  Our customers have been hounding us to “do it again” and we’ve responded with the introduction of the DLIII.

The DLIII is a killer DAC featuring the latest balanced D to A converter, the TI PCM1798DB at its heart.  This stunning new generation of 192kHz processors from Texas Instruments (formerly Burr Brown) features 24-Bit resolution, and 123dB dynamic performance, and its rated THD is just 0.0005%.  Not only that, but it comes with differential outputs and an 8 times oversampling filter.

Our engineers based the DLIII around this amazing DAC engine, and designed an all new input circuit and receiver, a 100% discrete output stage and a huge power supply to finish it off.

Input circuitry and sample rate conversion

So much today is recorded onto computers, distributed audio and hard drive systems that we decided to add a high end USB computer interface in addition to the standard optical and coaxial SPDIF inputs. 

So, the DLIII allows you to connect one of three input types to the DAC’s receiver.

The receiver in a DAC is a critical component.  It takes the serial data stream (everything in one straight line of data) and converts it to a parallel stream and separates out the clock.  This function is the first place a DAC can make or break the way it performs, and here we used the hottest new receiver on the market, the 192kHz Crystal CS8416 with its extremely low-jitter performance (around 50 ps after we reclock it later in the process).

Once the data has been separated by the receiver, it’s sent to the astounding TI SRC4192 high-end sample rate converter.  Now here, regardless of the original sample rate your USB, SPDIF or Optical source has (typically 44kHz) we take the data and upsample it to 192kHz.  The TI device is the finest made today and maintains low distortion during the upsample process.

Once the sample rate has been converted, it is sent to the TI PCM1798 balanced DAC and its output is fed into our unique output stage.

DAC’s convert the digital signal into current.  Unfortunately, to play music through our systems, we need voltage.  So the first job of the all important output stage is to convert the current output of the DAC to a voltage, then amplify it so our preamplifier can play it back through the power amp.

99% of every DAC on the planet uses an op-amp to convert the output of the DAC to a voltage. We learned years ago that this is the worst thing you can do for the sound, because op-amps all have two major problems when used for this function: feedback and speed issues.

Without getting too technical, the greatest opportunity for a bright and edgy “digital” sound is caused by op-amp based current to voltage converters (IV converters) because the high speed of the DAC’s output causes transient or slewing induced distortion in the op-amps (SID).  SID is a combination of feedback and transient response issues that some exotic high-speed op amps can come close to handling, but all have a problem with it.

PS Audio’s engineers avoid the SID harshness by eliminating the feedback of the IV stage.  We do this by a unique single transistor IV converter with no feedback.  Speed issues and SID issues are completely eliminated with this technique.

Active and passive filtering

Once the signal has been converted to a voltage, the next potential sonic weakness is found in the filtering.  All DAC’s produce switching noise that must be eliminated before it reaches your preamp/amp combination.  Most companies use a gain stage with active feedback filtering.  The problem with this approach is somewhat the same as we just encountered with the IV converter, feedback and speed issues.

To solve this, PS Engineering uses a passive first stage filter to lower the noise before it enters the gain stage.  This is a simple technique that completely eliminates the hardness associated with active filtering. 

FET discrete output stage

Next to last, the gain stage itself which boosts the output of the DAC to the standard line level output required to play music.

For this challenge, PS Engineers stayed away from op-amps yet again, and built a 100% class A discrete FET based output stage.  This high-end stage uses sweet sounding FET’s at the input and low noise powerful bipolar transistors for the gain and output stage. 
 
Everything is direct coupled between the DAC output and the DLIII output so bass is  stunning in its power and impact.

 

 

Power supply

Last, but certainly not least, is the power supply.  Everything we do to help the sonics of our product be the best in the world would be for naught if we had a small power supply.  We’ve seen everything from the wall mounted transformer supplies (shudder) to power amp size power supplies.  Bottom line is this: if you want high-end performance you need a high-end power supply.

Inside the DLIII is a huge transformer, coupled to many thousands of microfarads of capacitance, Linear Technologies regulators and high speed, low noise diodes.  We have taken every effort to make the DLIII as good as it gets.