ЦАПы — Cayin RU9

The RU9 is a battery-powered converter with a built-in headphone stage, made by Cayin in Zhuhai, Guangdong, China. It goes well beyond the usual dongle format by adding a KORG Nutube 6P1 vacuum tube, an internal battery, Bluetooth reception and a coaxial port, and it was launched at USD 499 or EUR 598.

Key specs that matter

An XMOS XU316 processor receives USB data and passes it to a pair of AK4493SEQ converters, one per channel. Cayin promotes PCM up to 32 bit and 768 kHz and native DSD512, while the USB input itself is specified for 44.1 to 384 kHz and DSD64 to DSD256. In battery mode the 3.5 mm headphone output is rated at 160 mW into 32 ohm and the 4.4 mm balanced output at 400 mW, with THD+N of 0.006%, SNR of 114 dB and 112 dB respectively, 115 dB dynamic range and output impedance of 0.5 and 1.0 ohm. Fixed line outputs deliver 1.2 Vrms single-ended and 2.4 Vrms balanced. The body measures about 100 x 70 x 15 mm and weighs 150 g, and a 3.85 V 2000 mAh cell gives roughly 3.1 to 4.7 hours depending on mode and output, with about 1.3 hours to recharge.

Engineering and use context

A short press on the menu button switches the analogue stage between three paths. Transistor mode leaves the tube out of circuit, Classic runs the Nutube with negative feedback off, and Modern runs it with feedback on. A BAT/DC switch lets the unit draw from a separate USB power port instead of its battery, and in this DC mode the balanced output climbs to about 1 W into the same load. Inputs cover USB, Bluetooth with LDAC and aptX HD, and S/PDIF through the coaxial socket, which can also act as a digital output. The menu offers three gain levels, three line-out levels, UAC 1.0 or 2.0 for compatibility with some game consoles, six PCM filters and two DSD filters. A small TFT screen shows source, gain, volume and sample rate, while a coloured LED indicates the incoming rate. Physical keys handle track skipping and play or pause, and a leather case comes in the box.

Pairing

The supplied Type-C cable and USB-A adapter link the RU9 to phones, tablets or computers, and Windows may need Cayin's driver. Both jacks have a low source impedance that makes them a good fit for earphones, while DC mode helps with harder-to-drive full-size headphones. The line outputs can feed a desktop amplifier or powered speakers.

Alternatives

Cayin's RU7 is a smaller USB dongle DAC built around a discrete 1-bit resistor network that converts every signal to DSD before conversion.