Cayin C9 Portable Headphone Amplifier

The Cayin C9 is a reference portable headphone amplifier: fully balanced and fully discrete, for players and DACs with a line or pre-amp output. It offers two timbres, KORG Nutube tubes or a JFET solid-state stage, and Class A or Class AB operation, and delivers 2,600mW per channel into 32Ω balanced, enough for demanding planar headphones as well as IEMs. It runs straight from four 18650 batteries in a removable module.

Tube or solid-state timbre

A tailor-made, fully balanced four-channel dual-timbre circuit gives you the choice of a pair of KORG Nutube 6P1 double directly heated triodes or a quad set of Toshiba 2SK209 JFETs, on both the single-ended and balanced outputs.

The redesigned tube circuit uses carefully applied feedback to keep THD+N to 0.03%, for what Cayin calls a euphonic, lively sound with delicacy. To stop the Nutubes picking up vibration, each sits in Cayin’s installation kit: a custom shock-absorbing silicone housing, a spring-loaded suspension and a flexible printed circuit, first developed for the N8 player.

The solid-state circuit is a fully discrete buffer and amplifier built around two matched pairs of high-quality, low-noise Toshiba 2SK209 audio JFETs, for a warm, rich timbre that is realistic and engaging.

Class A or Class AB

Switch the amplifier instantly between Class A, less efficient but with low distortion and a musical, smooth, warm and lush sound with lovely vocals, and Class AB, more efficient and dynamic, with a clean, tight, extended sound with authority and slam. Choose by music, headphones or simply preference.

Gain and volume

Two gain stages are set automatically by the microcontroller: a custom 6dB voltage gain circuit, and the gain in the electronic volume control. Volume is set by a four-channel ALPS potentiometer driving a pair of low-noise, low-distortion MUSES resistor-ladder electronic volume chips, for precise, satisfying control.

Line or pre-amp input, any connection

In Line mode the C9 takes a fixed line-level signal and works as a headphone amplifier with its own volume control. In Pre mode, switched on with the PRE activator on the side, it takes a variable pre-amp signal and works as a power amplifier, with the volume set on the source. The inputs and outputs are never limited by the sockets: balanced in to balanced out, single-ended to single-ended, single-ended to balanced, or balanced to single-ended.

Fully discrete headphone amplifier

The four-channel JFET and BJT amplifier is fully balanced. The input signal passes through a quad set of WIMA coupling capacitors to two matched pairs of LSK489 dual JFETs as the differential amplifier, and the output stage is a matched quad set of doubled bipolar transistors in parallel, with ample power for IEMs and headphones. Cayin’s diagram also shows C0G and POSCAP capacitors, a DC servo and Class A/AB bias adjustment for each half of each channel. A pyrolytic graphite sheet on the hottest parts and careful component placement keep the C9 consistently cool.

Direct battery power

Four Sony VTC6 3,000mAh 18650 cells, with 8–12mΩ internal resistance and 30A continuous discharge, are connected in series for a ±8.4V supply with no boost converter, and a decoupling network gives low-impedance, fast-responding power. A protection and management system charges all four cells at the same pace, the USB-C port supports QC3.0 and PD fast charging, and LEDs show charging and battery level. The module is user-replaceable: spares can be bought separately and work as a standalone 18650 charger.

Good to know

• The C9 is an amplifier only, with no DAC or USB audio input. Feed it from a player or DAC with a line or pre-amp output.
• Battery life depends on mode: about 15 hours in Class AB with solid state, about 5.5 hours in Class A with the tubes. Charging can take longer if the four cells are at different charge levels.
• In the box: C9 with battery module fitted, rear glass protector, CS-35C35 3.5mm and CS-44C44 4.4mm interconnects, USB-C charging cable, spare battery-module screws, T6 screwdriver and user manual.
• For the newer flagship version see the Cayin C9ii.