Audio Note DAC 4.1x

HifiCritic Review — Positive Feedback Review

Extensive research into the fundamental properties of the data stream itself have shown beyond doubt that, regardless of the theoretical advantages of the signal manipulation employed in our competitors products, such as higher over sampling, noise shaping, re-clocking or jitter reduction, these corrective measures greatly interfere with the critical time domain requirements of the signal.

Music is a time continuum from start to end which when broken is irreparably damaged, and no amount of clever manipulation can restore it to its original time / frequency / amplitude duration or relationship, regardless of what the theorists may tell you.

As a result, we have developed a way of excluding or bypassing all these corrective measures, to allow the conversion from digital to analogue to be done without any manipulation whatsoever. All we do is to reformat the data stream to allow the converter chip to be able to interpolate the incoming information correctly.

In other words, the Audio Note (UK) DAC4.1x has no over sampling, no jitter reduction, no noise shaping and no re-clocking. Having removed all of the digital filtering that is required for over sampling, all filtering is done in the analogue domain where it is easier to retain good, wide band phase-frequency and dynamically coherent behaviour. It uses the highest grade Analogue Devices AD1865, 18Bit stereo converter chip solely because we found it to be the best sounding available (yes, even better than the 20Bit versions!).

The filter-interface coils / transformers are of the highest possible quality, using 80% nickel Super mu-metal cores. The air gaps in the two filter coils per channel are matched across the full frequency range to within 0.1dB of each other, using a specially designed program to supplement an Audio Precision System 2 test rig.

The DAC4.1x Balanced features an upgraded version of the M6 Line pre-amplifier output stage, using the 5814a and 6463 double triode valves. This is coupled to an output transformer, wound with Audio Note (UK) copper wire on a High B C-core. With a 33:1 step-down ratio, this output transformer not only has exceptionally wide frequency response, but also just about the absolutely best dynamic transfer function possible. The analogue output has provisions for both unbalanced and balanced operation, using the best available quality RCA and XLR connectors.

The DAC4.1x Balanced Signature features an upgraded version of the M6 Line pre-amplifier output stage, using a pair of 5687 double triode valves. This is coupled to an output transformer, wound with Audio Note (UK) copper wire on a High B Ccore. With a 33:1 step-down ratio, this output transformer not only has exceptionally wide frequency response, but also just about the absolutely best dynamic transfer function possible. The analogue output has provisions for both unbalanced and balanced operation, using the best available quality RCA and XLR connectors.

To power this spectacularly revealing arrangement, we have incorporated a dual channel power supply with double choke filtering and valve rectification. This technique not only provides excellent isolation between the digital circuitry and power supply, but also provides well-isolated short and clean analogue signal paths. The digital power supply is an exceptionally low noise, shunt-type.

​Internal component quality of this calibre has never before been seen, in either consumer or professional equipment. There is an abundance of Audio Note (UK) capacitors, and Audio Note (UK) Tantalum film resistors throughout the circuit. Analogue stage filter inductors and internal wiring are all produced with Audio Note (UK) wire.