Aune Audio BX2 Magnum Portable Headphone Amplifier

The Aune BX2 Magnum is a portable headphone amplifier with two Korg Nutube 6P1 vacuum tubes, a fully balanced four-channel discrete circuit, and up to 5 watts of output into 32 ohms, all running on its own seven-cell battery.

The BX2 Magnum is for listeners who want one amplifier for the desk and the bag. Feed it from a DAP, portable DAC, or desktop source through 3.5mm, 4.4mm balanced, or RCA inputs, and it drives IEMs and full-size headphones from 3.5mm and 4.4mm outputs, with a choice of tube or transistor sound.

Tube Mode and Transistor Mode

A physical switch selects tube mode or transistor mode. The two signal paths are fully independent, and latching relays handle the switching so the unused path stays out of the signal. Transistor mode is fast and linear, with THD+N of 0.0003% from the balanced output. Tube mode routes the signal through the Nutubes for the warmth, body, and harmonic richness people buy tube amplifiers for, and its distortion rises to as much as 1% as a result.

Two gain levels and two current settings add more options. Between mode, gain, and current, the BX2 Magnum has eight combinations to match different headphones and music.

Korg Nutube 6P1 Tubes

The Korg Nutube 6P1 is a dual-triode vacuum tube, and in the BX2 Magnum both tubes do real work in the amplification stage. A dedicated 30V anode supply runs them in their linear range, which gives them more voltage headroom than most portable tube stages have. Ahead of the tubes, a twin JFET input stage adds its smooth transfer characteristic, and the fully balanced four-channel layout keeps left and right separate for precise imaging.

Battery and Power Supply

The BX2 Magnum's 14,000mAh battery is made of seven separate 2000mAh cells. Six of them form a plus and minus 12V supply for the analog circuit, and the seventh runs the digital controls on its own, which keeps control noise out of the audio. Two four-segment indicators on the rear panel show the charge of both banks.

A full charge over USB-C takes about five hours and lasts up to 13 hours in transistor mode or more than 8 hours in tube mode.

Desktop Use with the BP1

A five-pin external power input lets the BX2 Magnum bypass its battery and run on plus and minus 15V from Aune's BP1 external power supply, sold separately in a matching stackable chassis. At the desk it runs on higher supply rails than the battery provides, and away from the desk the battery takes over.

Measurements and Power

Aune specifies output noise of 3 microvolts or less and a signal-to-noise ratio above 117dB, figures in line with good desktop amplifiers. A 31-step R2R digital volume control keeps the channels matched at low listening levels with no contact noise. High gain delivers 5,180mW balanced into 32 ohms and 644mW into 300 ohms, enough for demanding planars and high-impedance dynamic headphones. Check your own headphones against the table below with our headphone power calculator.

How the BX2 Magnum Compares

Its closest relative is Aune's desktop S17 Pro EVO, which shares the twin JFET input and adjustable current, with more power and a wall plug. The BX2 Magnum brings that design to a portable amplifier and adds something the S17 Pro EVO does not have: vacuum tubes and a second sound signature. At $799, few portable amplifiers offer vacuum tubes, a transistor mode, and 5 watts of balanced power in one chassis.

Key Features

• Portable headphone amplifier with tube and transistor modes
• Dual Korg Nutube 6P1 vacuum tubes in the amplification stage
• 30V anode supply runs the tubes in their linear range
• Fully balanced four-channel discrete architecture with twin JFET input
• Physically independent signal paths with latching relay switching
• Up to 5W into 32 ohms; 5,180mW balanced at high gain
• Two gain levels and two current settings
• 14,000mAh seven-cell battery: six cells for +/-12V analog, one for digital
• Up to 13 hours battery life in transistor mode, over 8 hours in tube mode
• External power input for the BP1 power supply (sold separately)
• 31-step R2R digital volume control with precise channel matching
• 3.5mm, 4.4mm balanced, and RCA inputs; 3.5mm and 4.4mm outputs
• Output noise 3uV or lower; SNR above 117dB
• All-aluminum CNC chassis in black and gold
• USB-C charging at 5V/2A
• Hi-Res Audio certification

Technical Specs

Headphone Output Power (High Gain)

What's in the Box

• Aune BX2 Magnum portable headphone amplifier
• 3.5mm to 3.5mm cable
• 4.4mm to 4.4mm cable
• USB-C to USB-C charging cable
• Velvet pouch
• 4 spare silicone feet
• Quick start guide and warning card