New from Cayin: the RU6 — the world’s first (?) R-2R dongle DAC, featuring an in-house developed 24bit discrete resistor array for PCM decoding up to 384kHz and DSD up to DSD256*. According to the Chinese manufacturer, the resistors are “1/1000 ultra-high precision TCR25 low-temperature coefficient thin film” and have sufficiently low power draw to maintain compatibility with smartphones as well as PCs and Macs. Host device connection comes via USB-C.
From the press release: “The basic idea of R-2R ladder is a matched pair of two resistors, the first is “R” and the other is “2R” which has twice the value of R. To achieve 24bit decoding, we need 48 resistors (23 x R and 25 x 2R) for one channel. So for a stereo 24Bit R-2R decoder, we need exactly 96 resistors.”
A function key on the side of the RU6’s CNC-d aluminium chassis, which also sports a 1-inch 128x64px OLED screen, allows this dongle DAC to operate in one of two modes: 1) an oversampling mode that sees all incoming streams upsampled to 384kHz for “improved detail retrieval and frequency extension” but with the minor penalty of filter ringing; and 2) a NOS mode that bypasses the upsampling (and therefore digital filters) for “low phase distortion, low jitter and an absence of ringing artefacts”.
Sitting next to the function button are the volume up and down buttons. Like the RU6’s D/A conversion, internal volume control is executed via “a high precision resistor array volume control circuit that provides 99 steps of volume control through 9 segments of resistors and switching relays.” The upshot is that a full volume signal must be extracted from the host device and bit-perfect playback apps – like UAPP or Audirvana – are recommended (but not essential).
The press release goes on to say: “However the Resistor Array volume control involves switching relays and we need to mute the output for a short moment when a relay kicks in, otherwise users will hear a pop noise from the relay. This will introduce a small delay in volume adjustment, a small price to pay in order to implement R-2R resistor ladder network in a dongle DAC.”
Cayin is also keen to point out that the RU6’s digital and analogue circuitry reside on separate circuit boards.
At the RU6’s business end sit two headphone outputs: a 3.5mm single-ended socket that promises 0.5 Ohm output impedance and a power output of 138mW into 32 Ohms; plus a balanced 4.4mm Pentaconn socket that pushes 213mW into 32 Ohms from 1 Ohm of output impedance. Switchable high/low gain assists with headphone/earphone matching.
Further information: Cayin
*Footnote #1: DSD bitstreams are converted to PCM 384kHz upon entry.