Cayin HA-6A MK2 KT88 Tube Amplifier with External PSU

The Cayin HA-6A MK2 is a single-ended Class A tube headphone amplifier with KT88 output tubes, tube rectification and a separate power supply chassis, the long-awaited successor to the HA-6A. Cayin’s own output transformers match it to headphones from 8 to 600Ω, it delivers up to 4,500mW (4.5W) per channel in ultra-linear mode from its 4-pin XLR output, and a pre-amp output lets it run a speaker system too. The whole circuit is hand-wired point to point.

Compared with the original HA-6A, the MK2 moves the power supply into its own chassis, upgrades the rectifiers (JJ GZ34/5AR4 instead of 22DE4) and the drivers (JJ 12AU7/ECC82), swaps the EL34 output tubes for Genalex Gold Lion KT88s, lowers distortion from 1% to 0.3% and raises the signal-to-noise ratio from 98dB to 104dB, and adds a pre-amp output and a remote control.

Single-ended Class A with KT88s

Two 12AU7/ECC82 dual triodes handle the voltage gain under highly linear conditions, preserving fine detail and layering. A matched pair of Genalex Gold Lion KT88s then delivers the whole output in single-ended Class A, and two JJ GZ34/5AR4 rectifiers keep the high-voltage supply stable. Cayin set the operating current of each tube stage independently and paired it with a pure, stable supply, for the rich tone and musical depth single-ended Class A is known for.

With over 30 years of experience in tube selection, Cayin hand-tests and matches every tube against strict performance standards.

Triode or ultra-linear

A front-panel switch changes the output tubes’ operating mode at any time, so you can compare in real time. Triode mode is soft, elegant and naturally warm, ideal for vocals, jazz and acoustic music. Ultra-linear mode gives wider dynamics, tighter bass and better control, and suits orchestral music and film soundtracks.

An outboard power supply

The power supply sits in its own chassis, separated electrically, magnetically and mechanically from the amplifier circuit, for clean, quiet power, a darker background and an excellent signal-to-noise ratio for a tube amplifier: 104dB (A-weighted). That makes it a good match for sensitive headphones too. A multi-stage tube-regulated supply feeds each amplification stage independently, minimising ripple and crosstalk. A custom silver-plated 6N copper umbilical cable joins the two chassis, the rigid, damped cases isolate vibration and help heat escape, and a 60-second soft start lets the tubes warm up and settle before the sound comes on.

Built by hand with in-house transformers

Cayin makes its own transformers: a custom toroidal power transformer with high-purity copper windings for low magnetic noise, in a shielded, encapsulated housing with extra circuit protection, and wide-bandwidth EI output transformers for minimal signal loss. Every component is soldered by hand with classic point-to-point wiring, keeping signal, power and ground paths independent. Silver-plated signal wiring, AudioCapX coupling capacitors from the USA and Japanese electrolytic capacitors complete the circuit.

Outputs for every headphone

Cayin’s newly developed output transformers adjust gain and output impedance in three steps: low (8–64Ω), mid (65–250Ω) and high (251–600Ω). Headphones connect by 6.35mm, 4.4mm or 4-pin XLR. The 4-pin XLR is the full-power balanced output; the 4.4mm output is deliberately quieter, with a better signal-to-noise ratio for sensitive headphones and IEMs, and can also help if a system picks up hum. Matching the impedance gives a natural sound with well-defined bass; planar headphones are especially sensitive to it, so try the settings once you know the sound. A higher setting gives more output power, because it drives a harder load, unlike a solid-state gain switch. Dual VU meters show the level of each channel.

More than a headphone amplifier

The RCA pre-amp output (up to 6V, 20dB gain) lets the HA-6A MK2 drive active speakers or a power amplifier, so one device serves both headphones and a small hi-fi system; a rear switch selects pre-out or headphones. Sources connect by RCA or balanced XLR, chosen with a front switch.

Built for tube rolling

Many alternative tubes are supported. For the KT88s Cayin lists EL34, KT66, 6CA7, 6L6, KT77, 6550, KT90, KT120 and KT150. For the rectifiers it lists GZ34, GZ37, 5AR4, 5V4G, 5R4G, 5U4G, 5Y3GT and 5DJ4, and for the drivers 12AU7, ECC82 and ECC802S (see the tube substitution table in the manual). A Japanese ALPS potentiometer gives smooth, precise volume, the aluminium remote sets volume and mute, and the newly designed cages protect the tubes and stop accidental contact with them when hot.

Good to know

• This is an analogue amplifier with no DAC. Connect a DAC or source with RCA or XLR outputs.
• It is two boxes, about 19kg in total, and needs space and ventilation for the tubes.
• Colours: black or silver front. In the box: amplifier and power supply, tubes, tube cages, power cable, remote control and user manual.