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Digital Audio The sonic character of recordings made using digital audio technology has been controversial since before the CD was launched over twenty years ago. Many have felt that the best music recorded using the "Red Book" CD standard (16 bits/44.1KHz sampling rate) was markedly inferior to that commercially available on the long playing record. As a result, many music lovers have reluctantly embraced the CD medium as a means to add music to their collections. Excellent CD playback capability has been available for perhaps 5 or 6 years, but requires "big bucks". Well, that reluctance and big financial outlay are a thing of the past with the RAKK dac. 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 need a RAKK dac Mk II kit, a power supply (12VDC), and an analog output stage. Please see further information about power supply kits and analog output stages below that were designed to work with the RAKK dac Mk II.
RAKK dac Kit: $369 ($319 for purchasers of the original RAKK dac Kit.) Power Supply and Output Stage Kits For a complete audio D/A converter you must add two supporting functions to the RAKK dac Kit :
The power supply must provide 12VDC at about 240mA. Because the RAKK dac provides a low-level current output directly from the DAC chip, additional circuitry is required on an output stage board to provide current-to-voltage conversion, isolation, and gain. To help you complete your RAKK DAC based D/A converter, we have various supporting kits available.
RAKK dac Power Supply Kit For those of you who want to "roll your own" output stage or purchase the Passive Output Stage Kit, we have designed an excellent, compact standalone 12VDC supply. It features sonically advantageous Minimal Reactance with extensively bypassed regulation and a low stray field toroidal power transformer. These power supplies can be wired for 100VAC, 120VAC, or 230VAC mains operation. The RAKK dac Power Supply Kit exists in two versions. The Basic RAKK dac Power Supply Kit meets the needs of the RAKK dac Mk II at an economical price with very good sonic performance. The Premium RAKK dac Power Supply Kit adds AC line filtering and more extensive output bypassing for the very best power supply support of the RAKK dac Mk II.
Basic RAKK dac Power Supply Kit: $89 Premium RAKK dac Power Supply Kit: $119 Passive Output Stage Kit The current output of the PCM1794 is high enough to enable use of a Lundahl LL1674 1:4 step-up amorphous core transformer for a passive output stage. A special connection of the primary is used to very effectively cancel the DC bias voltage present on the output terminals of the PCM1794. A high quality Mills resistor in the secondary circuit of the transformer provides for the current-to-voltage conversion. This output stage is actually small enough so that it is physically the same size as the RAKK dac board and can be stacked on top of it for a particularly compact installation.
Output level at 0dBfs: 2.0vRMS
Passive Output Stage Kit: $299 Active Output Stage Kit The differential class-A triode parafeed output stage is a further refinement of the circuit used in the excellent Raleigh Audio Line Stage detailed in the November 2004 issue of AudioXpress magazine. This output stage uses a transformer-coupled output in a bridged parallel feed configuration that was used by Western Electric over 60 years ago. However, it employs a cascode connected depletion mode MOSFET constant current source (CCS) that is more effective than anything available to Western Electric engineers. The output transformers are the superb amorphous core Lundahl LL1674 units. The amplifying device is the Russian 6N6P dual triode. For DAC applications, current-to-voltage conversion is accomplished using high quality low value resistors. Dual high-voltage Minimal Reactance Power Supplies are integrated onto the Active Output Stage board, so only a power transformer is required to provide a complete vacuum tube output stage solution. An optional volume control has also been accommodated in the implementation of the revised Active Output Stage Kit (see Stepped Shunt Attenuator). For combination DAC/line stage applications, an input transformer can be accommodated with the new Combo Input Stage Kit. In addition to being a superb RAKK dac output stage, this kit, together with the Combo Input Kit, can accommodate line level inputs. The kit uses all top quality parts, among them: Cardas film capacitors, Mills wire-wound resistors, Kiwame carbon film resistors, and Holco metal film resistors. The dimensions of the PC board are 9.7" x 6.1". A practical minimum internal height for an enclosure is about 3".
The new Active Output Stage kit is offered in two levels. The levels differ in the amount of parts provided versus the parts that you must procure on your own. The Level 1 kit provides the minimum parts, the Level 2 all of the parts needed. Level 1 Kit Included:
Your involvement:
Level 2 Kit Included:
Your involvement: Assemble the kit. Active Output Stage Kit, level 2: $849 Fully assembled and tested Active Output Stage: $999Extreme RAKK dac Kit
This kit provides you with a 24 bit 192KHz upsampled DAC that has a tube output stage of the highest quality. This unit has sonics superior to all of the mid-priced DACs that we have auditioned, and challenges some of the real heavyweights in the business, as well. The Extreme RAKK dac Kit supports both balanced (XLR) and unbalanced (RCA) outputs. There is no compromise in choosing one over the other. The standard digital input configuration is a single coaxial (RCA) S/PDIF input. Optional front panel switch selectable second inputs can be accommodated, including another coaxial, an AES/EBU (XLR), or a USB input (see below for details). 
Specifications
Second input (Coaxial or AES/EBU) with rotary selector switch and knob for front panel mounting: $75 Second input (USB) – we are developing a USB input option, but it is not yet available. The HagUSB Kit (www.hagtech.com) works well with the Extreme RAKK dac Kit by plugging the HagUSB output into the Coaxial input, if you need a USB input. Volume Control – The Extreme RAKK dac Kit has been designed to readily accommodate the Stepped Shunt Attenuator as a volume control for digital only systems, removing the necessity for a preamplifier: $225 |
1004 Olive Chapel Rd.
Apex, NC 27502 USA (919) 387-0911 Mon-Fri 8 a.m. - 5 p.m. EST
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We have combined the RAKK dac Mk II Kit, the Premium RAKK dac Power Supply Kit, and the Active Output Stage Kit in a custom designed enclosure similar to that used for the K&K Audio Single-Ended Triode Phono Preamplifier Kit. The power supplies for the digital circuitry and analog output stage are entirely separate to minimize cross-contamination.