Audio Note DAC 5 Special: Technical Background

Audio Note DAC 5 Special: Technical Background

A Review Preview

Constantine Soo

2 September 2003


DAC: Selected Analog Device 1865N 18-bit, 44.1/48/96KHz compatible
Receiver Chip: Crystal CS8414CS
Sampling Technique: Audio Note™ proprietary 1xoversampling™ direct from disc™
Digital Input Pulse Transformer: Audio NoteTM silver-wired mumetal cored toroidal, TRANS-278 x 1, TRANS-268 x 1
I/V Interface Matching: Audio NoteTM copper wired fully interleaved Supermumetal 250 cored transformer x 2 
Analog Filter: Audio NoteTM silver wired choke, Audio NoteTM paper in oil copper foil capacitor 
Output valve stage: NOS 5687 double triodes x 2, in series with output transformer
Output Transformer: Audio NoteTM silver-wired Radiometal double C-core with 0.2mm laminations x 2
Digital Inputs: Audio NoteTM Silver plated RCA (1), XLR (1) switchable
Analog Outputs: 1 pair, L and R (RCA) 
Weight: 22 Kg
Dimensions: 145(H) x 450(W) x 425(D)(mm)
Fuse Rating: 1.6A anti-surge (110/120v supply), 800mA anti-surge (220/240V supply) 
Reference output: 3.2V RMS 
Output impedance: 4 Ohm Balanced or Single-Ended, with load switching
Channel Balance: less than 0.2dB
Tube compliment: 5687WB (two), standard Philips/ECG, 6X5WGT (two), standard Philips/ECG
MSRP: $29,500.00

Audio Note (UK) Limited
Unit C, Peacock Industrial Estate
Lyon Close
125-127 Davigdor Road
Hove, East Sussex, BN3 1SG

Prologue to Audio Note DAC 5 Special Review

Since the advent of the 44.1kHz, 16-bit medium in 1982, the high end audio industry has been engaged in a sweeping pursuit in refining the design and implementation of the digital format. 

Ongoing insights harnessed from this collective effort gave birth to advanced decoding processes such as jitter reduction, oversampling, upsampling, and DSP-based custom algorithms. Numerous superior mastering techniques such as JVC’s K2, Deutsche Gramophones Original Image-Bit Processing, Sony’s Super Bit Map processing, etc. have also emerged.

Most importantly, the intelligence and wisdom harnessed from a 17 year historic pursuit fostered the creation of the DSD SACD by Sony’s engineers in 1999.

Regarding SACD’s rumored ulterior agenda aside, Sony’s new DSD SACD digital audio standard in its augmentation of advanced data storage capacity conveyed a bandwidth surpassing that of the Redbook CD format, thus seemingly rendered obsolete the company’s monumental, 1982 contribution to the world. At the time of this writing, with music supplied from Sony’s own vault and that of an alliance of prominent record labels such as DMP, Phillips, Telarc and Universal Music Group, the brighter future of the high-resolution format is doubly assured by the additional support of highly visible hardware manufacturers such as Accuphase, DCS, Krell, Marantz and Panasonic. 

Overall, the current state of digital audio is one of incredibly complex mathematical processes in the forms of sampling rate manipulations and word-length extensions. Nowadays, practically all major CD player manufacturers incorporate processes that will either oversample or upsample the Redbook CD data to much higher sampling frequencies or higher bit rates. 

Among the handful of companies whose CD players do not perform either over or upsampling, Audio Note is best known in the high end circle for its steadfast advocacy in SET amplification. From this company that offers audiophiles the $90,000, 27 Wpc Ongaku integrated amplifier, comes a $30,000 DAC with no oversampling, upsampling, or digital filter: the DAC 5 Special. 

We shall examine the current state of the compact disc as defined by the British company in two articles: a technical background and a report on the auditioning. First the technical background.

Audio Note & the Super DAC

The DAC 5 Special is only Audio Note’s second costliest DAC, next to the $49,500 DAC 5 Signature. Still, in its internal price sheet, AN refers to the DAC 5 Special as the “Super DAC”. 

At the emergence of the aforementioned oversampling and upsampling movements during the late 90s, AN owner Peter Qvortrup chose not to partake in the new schemes as he was critical of the vastly presumptuous calculations generated by the techniques. He saw solutions to refining Redbook CD playback with his recognized expertise in using discrete components to create system synergy. In contrast to increasing the linearity of the digital-to-analog conversion process via oversampling and upsampling, Peter suggested concentration on exercising the utmost care in original signal preservation and amplification instead.

Peter developed the proprietary “1xoversampling™ Direct from Disc™” topology which he claims is more capable of preserving the low-level details and dynamic headroom embedded in the original data stream. The company designated the application of the Analog Devices’ 18-bit AD1865 converter chip and the Cirrus Logic’s Crystal CS8414 receiver chip to form the primary architecture of its converters. An in house designed and manufactured digital input transformer is used as the digital input matching device.

The DAC 5 Special utilizes more stringently selected AD1865 chips.

Also unique among similarly priced DACs in the world, AN’s DAC 5 Special is the only other DAC that is given Audio Note’s proprietary, internationally patented copper wired “magic” I/V transformer interface, that actively couples the DAC chip’s output to a powerful transformer, which AN claims would yield superior bandwidth and dynamic envelope than passive or simpler I/V interfaces. 

In addition to the patented “magic” I/V transformer interface, the Super DAC also incorporates a premium amplification stage for sending converted signals through, a hand wired silver version of the aforementioned digital input transformer, hand wired silver-laden point-to-point PCB circuit, dual mono power supply with multiple regulation stages, copper wired interleaved Supermumetal 250 cored transformer, two NOS 5687 double triodes analog output stage with exclusive 33:1 ratio copper wired transformers, and a pair of R36 double C-core output transformers. 

Complimenting this assembly of heavy and precious metals are exotic parts such asBlack Gate electrolytes, assortment of ½ and 1% Audio Note™ tantalum film resistors, Cerafine capacitors and lavish silver wiring throughout.

According to AN, the extreme extravagance bestowed upon the DAC 5 Special is to capture extremely low-level details. Per AN, the use of the Supermumetal cored interface transformer, for example, is for the superior magnetic permeability from its 80% nickel content core, which in conjunction with a special bifilar wound bobbin provides a supposedly close to perfect magnetic coupling between the primary and secondary windings through the very permeable nickel core, thus enabling superior low-level signal behavior. Designed to uncompromisingly maintain signal linearity and dynamic contrast of the thus-extracted low-level signal is the NOS double triode analog output stage coupled to a powerful C-core transformer, effectively dispensing with the need for feedback signal correction, which AN believes compromises signal integrity. 

Additionally, the R36 C-Core output transformers designed and made by AN for use in the Super DAC are claimed to be capable of reproducing a bandwidth approaching the 5-200kHz frequency extension benchmark, which AN claims will not only preserve the feeble signals far better than other DACs’ capacitor coupled circuits will; but will also endow the Super DAC’s two pairs of single-ended outputs equal dynamic bandwidth and contrasts as its balanced one.

With all refinements taken together, AN claims the level of signal fidelity harnessed in the DAC 5 Special far exceeds that attained by DACs from any other companies by any other means.

Systems preparation

As Audio Note employs zero feedback output stages and relatively small output capacitors in all of its cheaper DACs, the company recommends coupling of all its DACs to preamplifiers with impedances above 47kOhm to avoid bass roll-off. Concurrently, AN advises its customers to ascertain the impedance of their non-Audio Note preamplifiers and experiment with Aux or Tuner inputs as needed, as some preamplifiers’ CD inputs carry the sub-optimal, sub-10kOhm rating. In the DAC5 and the other Audio Note™ DACs with output transformer, however, these impedance considerations are of no consequence as the output impedance of a DAC5 is below 4 Ohms and the DAC3.1x balanced for example is below 10 Ohms.

AN’s West Coast Distributor, Ray Lombardi, graciously provided the $35,000, complimentary M8 preamplifier for this review, replacing the $6,000 M3 that served initially. 

Thus, primary observations of the Audio Note™ Super DAC took place in the context of a $75,000, strictly AN system that was again, graciously provided by Ray, which included AN’s own $3,300 CDT-2 CD transport, the $16,500 Conquest Silver Signature 300B parallel monoblocks and the $20k AN-E SEC Silver loudspeakers. I checked the total dollar figure with at least 2 calculators already.

Secondary observations on the DAC 5 Special were made in a non-AN system consisting of 47 Laboratory’s $5,400 4713 Flatfish CD transport and Loth X’s $15,000 JI300 integrated 300B amplifier, driving, in rotation, the AN speakers as well as Italian speaker maker Aliante’s $11,000 Royal Device Laura Studio MK II with Miranda Horn loudspeaker system. German speaker maker ELAC’s top bookshelf mini-monitor, the CL330JET, British company Audion’s $15,000 Level 5 Golden Dream monoblocks, Linn’s $9,000 Klimax Twin stereo power amplifier and the Reference Line Preeminence Two passive preamplifier with the Preeminence One Signature amplifier also partook into the auditioning and provided additional insights. 

Last but not least, Peter Qvortrup graciously sent from England his top-of-the-line, 99.99% pure silver 42-strand symmetrical litz “Sogon” digital cable, interconnects, as well as the 20-strand 99.99% pure silver AN-Vx interconnects and the 27 strands 99.99% pure silver litz conductors AN-SPx speaker cables for this review. 

All aforementioned equipment that are not yet reviewed will be featured in separate writing. My next installment will detail my experience with the Super DAC, as well as my viewpoint on what it represents in the current high-end audio environment. Stay tuned.


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