was designed from a blank page as a third generation pulse width modulation audio digital to analog converter kit bringing the latest circuit advances to home audio builders. It is expandable and upgrade able. The designers intent is that it can be configured and customized to meet its owners exact needs and tastes, now and in the future. X-DAC represents our best efforts. We have no "reviewer's darling" salon line or in line jitter filter products to protect. With an enthusiasts naiveté we designed in a brand new sample rate conversion chip as a jitter firewall. The rest of the industry deemed this part, the AD1891, as too expensive. We listened then measured and deemed it too good to ignore. Its effect on the music too profound to do without. But no single part or technology makes quality. It is the synergistic combining of parts in a thoughtfully designed and optimized whole that results in musical magic.

The 3.0 in X-DAC's name denotes it as a third generation converter. We consider the generations of home digital high-end audio to have gone something like this:

• First generation, well perhaps the less said the better! Sound of these products drove many music lovers back to analog. Towards the end of the first generation pioneering audiophiles and manufacturers discovered that quality analog sections and power supplies are as important to digital audio as they always have been in analog.
• Second generation saw the evolution of DAC chips capable of true 16 bit linearity. Many were also shocked to learn that the digital parts of the circuit could have a profound effect on the final sound. It seemed bits were not just bits after all! The data source and even the connecting digital cable seemed to effect the final results. Despite this later second generation converters sound very fine. Indeed many of these remain in production with new 2nd generation designs continuing to appear.
• Third generation dawned when the best designers having mastered DACs, power supplies, analog sections, and digital filters asked "what's next, what is still causing distortion?" The answer that swept through the industry is jitter. Simply put jitter is the uncertainty or inaccuracy of a clock signal. To accurately reconstruct an analog signal stored as a stream of numbers we must get both the amplitude and timing of each sample correct. When during the second generation DAC chips became available with accuracy of 16 to 20 bits the variations in clocking out these bits came to dominate the error functions of the devices. With other sources of non-linearity minimized distortion caused by jitter inducing effects such as cable reflections and indifferently designed data sources became readily audible to critical listeners and the topic of much, sometimes heated, discussion. This newly rediscovered error source has generated a spate of products; cables, transports, and data reclockers in addition to new or revised DAC designs taking jitter into account.

INPUTS

One to four inputs can be installed with coax S/PDIF, balanced AES/EBU, and Toslink optical formats all supported. The finest transformers specially developed for digital audio serial links preserve the input signal while keeping source and cable ground noise at bay. The Crystal Semiconductor CS8412 is used to recover the clocks and audio data from the serial link. Carefully developed circuit board layout and a dedicated LC filtered power regulator allow it to perform at its best.

DSP Port & EXPANSION AREA

After the audio data, word clock, bit clock, and 192 Fs clock are recovered by the CS8412 they are brought out on this port. Normally jumped to the next stage this port allows future expansion by making the data and clocks easily accessible. The expansion area was left open and provided with power and ground connections to allow for future function module plug ins.

3 Hz SRC JITTER FILTER & MASTER CLOCK

The critical master integrator clock feeding the CS4328 is taken from a local crystal not from a Phase Locked Loop (PLL). The crystal is excited to form the master clock in a low stress low jitter circuit featuring two separate regulators double LC de coupled off the analog supply rail. This is made possible by using the Analog Devices AD1891 asynchronous sample rate converter chip to break the synchronous nature of all previous S/PDIF format audio DACs. As well documented in the world audio press and Audio Engineering Society publications synchronous audio DACs suffer the effects of jitter introduced into the clocks recovered from the input data stream. Jitter is introduced by the data source, the wire or optical media carrying the serial S/PDIF data stream, and unavoidably by the compromise inherent in combining the data and clock into a single data stream. With typical gold plated sledge hammer engineering many in the high end design community have gone after the jitter problem with multi thousand dollar transports, non-standard two wire interfaces and ultra wide bandwidth implementations of S/PDIF and AES/EBU. While great fun to write about and play with for well funded audiophiles, all these solutions struck us as 'hot-rod' audio. Not well suited to a real world which promises a wealth of digital sources now and in the future. A single source system featuring an $8000 CD transport is fine if that is what you want and can afford. We want the same superior results if the data stream comes from sources we can not or choose not to gold plate like digital music services from cable TV or satellites. One can hardly ask the local cable company or not so local satellite operator to kindly lower the jitter on channel 30 because I want to hear more of the body of Yo Yo Ma's cello! But I DO WANT TO HEAR THE WOOD IN THAT CELLO'S BODY! And in our experience it is lowering the jitter in the critical clocks inside audio DACs that allows these fine details and the emotional impact they carry to shine through. The technology of asynchronous jitter reduction allows breaking the synchronous bond between S/PDIF format audio DAC's and their data sources. Operating as truly asynchronous devices we finally have digital audio as it was meant to be, the only concern being is the data error free, NOT is it error AND jitter free. The AD1891 ignores jitter above 3 Hz. Unlike nested PLL jitter filters the input PLL can be left 'wide open' assuring quick locking to all sources and sample rates. Asynchronous operation of the CS4328 further tightens and appears to extend the bass. The already excellent highs are elevated another notch. Jitter adds distortion throughout the frequency range of PWM and bit stream DACs, feeding a pure clock to the device finally allows its inherent purity to shine through in the critical midrange. This improved midrange clarity may be the best dividend of asynchronous jitter reduction. (Click to document re: Robert Harley's AD1890 bashing in Stereophile.)

DAC

The critical DAC is Crystal Semiconductor's CS4328 which integrates a digital 8x interpolation filter, 64x oversampling - modulator, reference voltage generator, and ultra-linear analog low-pass filter. Signal paths within the DAC system are microscopic in dimension reducing interference effects both into and out of the system. Integrating the digital and analog filters allows them to be designed with complementary characteristics. The result is only ± 0.5 of phase shift from 20-20,000 Hz allowing very precise sound staging properties. Unlike many pulse width modulation DAC chips which compromise using single + 5 volt supply the CS4328 has separate + 5 volt digital and ± 5 volt bi-polar analog supplies. Thus its built in amplifiers are very transparent and capable of driving a 600 ohm load.

ANALOG STAGE

Thanks to the anti-aliasing filtering already having been taken care of in the CS4328 the analog stage of X-DAC is more akin to a ultra fast wide band purist pre-amp then a typical DAC analog section. The phase distorting 3rd order filters used in other designs are not required. Fully DC coupled so there is no smearing from DC blocking caps. Transimpedance current feedback topology is used to eliminate any chance of slewing induced distortion. The resulting very fast high current output buffer shields the DAC system from the outside and give it a easy high impedance load. Relieved of the need to drive output cables and the following device's input impedance the CS4328's output stage settles down tightening up its bass to state-of-the-art levels. Owners preferring purist transparency over the last bit of bass slam can opt to omit the output buffers allowing direct drive from the CS4328.

DC in & Power Supplies

DC input is supplied from a proven reliable industry standard regulated 20 watt plug in power supply with export versions available. The regulated DC from the outboard supply is RFI filtered as soon as it enters the DAC and extensively de coupled throughout the board. Power supplies for the X-DAC 3.0 are numerous and over designed. The DAC chip and each output buffer have their own pair of regulators. Liberal use of low impedance Panasonic HF series electrolytic and WIMA polypropylene bypasses before and after regulators keep noise at bay and supply impedance low. The regulators are located right next to the devices they supply so wire impedance cannot prevent tight regulation.

Printed Circuit Board

The physical realization of the X-DAC 3.0 design is supported on a double sided fiberglass circuit board. Ground system is divided into three sections for Phase Locked Loop, Digital, and Analog subsystems. All holes for component mounting and signal vias are CNC drilled and plated through. Both top and bottom have solder mask and the top features a component placement silk-screened diagram. These details enhance both the circuit performance and the builders enjoyment during kit construction.

X-DAC 3.0 Measurements

NEW! X-DAC 3.0 Signature.

Click to X-DAC 3.0 review in Audio Electronics magazine.

NEW! Revised & expanded price table. X-DAC 3.0 Pricing

NEW! DAC kit feature comparision table. X-DAC 3.0 ACG's X-DAC 3.0 compared to PC's DAC-2

Power upgrade options information
Power upgrade options cost

X-DAC 3.0 Warranty

During the first 30 days after your X-DAC 3.0 kit arrives if for any reason you wish to return it do so and receive a full refund. This 30 day full refund warranty does include built kits if the resulting sound is not to your taste.

X-DAC 3.0 AJR & Syncro kits built according to our instructions, using the parts and power module supplied by Audio Crafters Guild carry a limited warranty for a period of 5 years. Factory assembled X-DAC 3.0 AJR units are also covered by this warranty. The terms of the warranty are simple.

1. Warranty period is 5 years from date of purchase.

2. Warranty applies to original and subsequent owners. Subsequent owners covered only if Audio Crafters Guild is notified in writing when the unit changes ownership.

3. Audio Crafters Guild will repair unmodified units at no charge to the customer during the warranty period.

4. The customer pays shipping charges both to and from Audio Crafters Guild when warranty work is required. Customer will contact Audio Crafters Guild for consultation and return authorization before shipping unit.

Due to the large number of variables out of our control the X-DAC 3.0 Board & Chips kit is NOT covered by the 5 year warranty.

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