It was a long time in coming, but the time spent was nothing compared to the sonic rewards. For those of you with original RAKK dacs, the new unit is physically and electrically compatible with your existing analog output stage implementation, whether you have a Passive Output Stage or Active Output Stage. The XO-DAC is no longer needed or beneficial. The original power supply is marginal from a capacity standpoint, because thе Mk II draws almost three times the supply current. A new power supply has been developed that has been sonically optimized for the Mk II. It is available in two versions, a basic one that meets the power supply needs and sounds very good ($79), and a deluxe version with AC line filtering and considerably greater capacitive bypassing at the output that sounds better yet ($109). These are also in stock.
Here is the Mk II description that will be up on the web page soon:
RAKK dac Mark II Digital-to-Analog Converter Kit
The RAKK dac Mark II is the result of an ongoing cooperative effort by K&K Audio and Raleigh Audio to bring you the cutting edge, affordable digital music playback solution.
Although we are proud of the original RAKK dac, we are continuously looking for ways to improve our products. For a product to be labeled “Mark II” it must exhibit a substantial improvement over the original.
Not content to let the original product alone, we experimented with the implementation of Asynchronous Sample Rate Converters – integrated circuits that input a digital audio signal at one sample rate and output the digital audio signal re-sampled at a different rate. In the course of researching the topic we had read of mixed results with ASRCs, but recognizing the potential benefits and wanting to hear for ourselves we embarked on a long, and occasionally frustrating, prototyping process. While evaluating designs incorporating ASRCs from 3 different manufacturers in a large variety of configurations we made some interesting discoveries. We found that an improperly implemented ASRC can destroy the sound by butchering the datastream. On the other hand we found that a properly implemented ASRC can substantially improve the sound. The process, commonly referred to as “upsampling,” has several potential sonic benefits. For example, a properly implemented ASRC process reduces jitter. Additionally, upsampling the digital audio datastream allows the DAC to operate at its maximum sample rate, where digital filtering can be accomplished well above the audio bandwidth, reducing the in-band sonic impact of digital filtering.
As a result of our evaluations, we settled on the TI/Burr-Brown SRC4192 as providing the most pleasing sound. With our implementation using the SRC4192, the improvement over the original RAKK dac is of major musical significance. We frankly had no idea that there was so much musical information captured on the CD medium. The best CDs are simply stunning to listen to now and are a challenge to the quality of the rest of the system, even if it has been optimized with an analog source.
For those familiar with the original RAKK dac, you will see the family resemblance. Again, we have employed the outstanding TI/Burr-Brown PCM1794 DAC, which is the latest generation current output 24 bit / 192KHz sampling D/A converter. Designed primarily for the high-end professional audio market, we found this converter to have the most lifelike sound. We couple this DAC with the 24 bit / 192KHz capable input receiver from Cirrus Logic, the CS8416. In addition to the word depth and sampling bandwidth considerations, the CS8416 has excellent jitter rejection specifications and a built-in digital input selection function. In addition to the digital audio integrated circuit building blocks described above, a first-class regulated power supply sporting dual regulation for the digital as well as the analog voltages is incorporated, along with extensive local capacitive power supply bypassing, and a carefully conceived layout. The analog section of the DAC is supplied with a shunt regulator for the best possible sound. All of these excellent-sounding design features have been retained in the RAKK dac Mark II.
Kit construction is a breeze -- most of the work is already complete. The 2.35" x 4.9" (6.0cm x 12.5cm) RAKK dac circuit board has all of the surface mount components pre-soldered to the top of the 4-layer PC board. You need only solder the digital input transformer(s) to the board to complete the kit.
The RAKK dac Mark II Kit has provisions for two digital inputs. Either or both of these inputs can be used. Designed into the PC board are jumpers for the selection of 75ohm or 110ohm input termination for each input. One Lundahl LL1572 digital input transformer is supplied with the RAKK dac Mark II Kit. An additional one may be purchased for the second digital input.
For a complete digital-to-analog converter, you will also need a power supply (12VDC) and an analog output stage. Please see further information about these below.
RAKK dac Kit: $349 (There is a $50 discount from this price for purchasers of the original RAKK dac Kit.)
Kevin Carter
K&K Audio
www.kandkaudio.com