DACs — Audio Note DAC 2.1x

Audio Note (UK) places the DAC 2.1x valve converter in its Level 2 group, whose criteria call for valve rectification and a higher grade of parts than Level 1. It is offered in three forms - the standard DAC 2.1x, the DAC 2.1x Signature and the DAC 2.1x/II Balanced - and the Signature edition is priced in the US at USD 4,900. The maker describes the converter as engineered for listening results in preference to a measured specification sheet, and the design deliberately leaves out network and computer connections.

Key specs that matter

Inside sits an Analog Devices AD1865N, an 18-bit stereo converter chip. Digital signals arrive through a 75 ohm RCA socket for S/PDIF or a 110 ohm XLR for AES/EBU, at 44.1, 48 or 96 kHz, and 24-bit files at 96 kHz are accepted but truncated to 18 bits. The reference output is 3.2 V RMS, with channel balance inside 0.2 dB. Output impedance is 600 ohm on the single-ended RCA outputs and under 10 ohm on the balanced outputs of the Balanced version. Each case is 145 mm high, 300 mm wide and 415 mm deep, and the unit weighs 5.1 kg. Buyers pick an anodised aluminium or a black acrylic fascia.

Engineering and use context

The signal path skips oversampling, jitter reduction, noise shaping and re-clocking, so the design runs without a digital filter. Filtering happens in the analogue domain using filter-interface coils and transformers wound by Audio Note itself, and the digital input is transformer coupled. The valve output stage works without feedback. The versions differ inside. The standard DAC 2.1x uses two 6DJ8 valves and solid-state rectification. The Signature adds a 6X5 rectifier valve for a valve-rectified, choke-regulated supply with its own mains transformer, and uses Audio Note tantalum resistors, copper coil capacitors and Black Gate capacitors. The DAC 2.1x/II Balanced moves to a full-size balanced chassis with two ECC82 (5814a) valves, an ECL82 and a 6X5, custom output transformers, both RCA and XLR outputs, and separate isolated supplies for the digital and analogue circuits.

Pairing

The two digital inputs take a CD transport or other source fitted with an S/PDIF or AES/EBU output. The single-ended versions suit preamplifiers with RCA line inputs, and the low-impedance balanced outputs of the Balanced version can drive XLR inputs.

Alternatives

The Audio Note DAC 1.1x/II uses the same AD1865N converter and input set but is built to Level 1 criteria with two ECC88 valves.