Allnic Audio HPA-300B

Reference-Class 300B Tube Amplifier for Headphones and Loudspeakers – Class A, Tube Rectification and 8 Watts of Output Power

The 300B is one of the most celebrated tubes in audio history. For decades, it has been admired for its natural midrange reproduction, spatial dimensionality and exceptionally organic rendering of voices and instruments.

With the Allnic Audio HPA-300B, Allnic combines this classic directly heated triode with a distinctly modern objective: an amplifier that delivers the characteristic sonic qualities of a high-quality 300B circuit while offering enough power and control for a wide range of today's high-end headphones.

And the HPA-300B is more than a headphone amplifier. With 8 watts of output power and dedicated loudspeaker terminals, it also functions as a fully fledged 300B integrated amplifier for efficient loudspeakers.

300B – the Single-Ended Triode in Modern Form

At the heart of the HPA-300B are two 300B power tubes. The directly heated 300B is remarkably simple in construction and, precisely for that reason, remains a favourite among tube enthusiasts.

Allnic does not use its characteristics to create an intentionally soft or excessively warm amplifier. Instead, the HPA-300B is designed around speed, transparency and control – without sacrificing the physical presence, harmonic richness and three-dimensional imaging that make a well-executed 300B circuit so compelling.

Choke Transformer Drive for the 300B

One of the HPA-300B's distinctive technical features is the use of a choke transformer to drive its power tubes.

Allnic combines some of the properties of traditional RC coupling with those of an interstage transformer, allowing the 300B tubes to be driven with particularly high control and speed.

The engineering effort can even be seen in square-wave performance: Allnic specifically highlights the amplifier's clean reproduction of a 10 kHz square wave – a demanding task for a transformer-coupled tube amplifier and a useful indication of the bandwidth and speed of its transformers.

Special Output Transformers for Headphones

In any 300B amplifier, the output transformers have a major influence on the final result. For the HPA-300B, Allnic therefore does not simply reuse transformers developed for a conventional loudspeaker amplifier.

Instead, the company developed compact output transformers specifically optimised for headphone use, designed to provide faster response and a broader usable bandwidth.

This is a fundamental part of the HPA-300B's philosophy: classic 300B musicality, but not at the expense of transient accuracy, resolution or speed.

5U4G / 5U4GB Tube Rectification

The power supply remains equally committed to a fully analogue approach. Instead of solid-state rectification, Allnic uses a 5U4G or 5U4GB rectifier tube.

For enthusiasts interested in tube rolling, this opens up further possibilities: different 5U4G and 5U4GB variants can be used, as well as compatible GZ34 / 5AR4 rectifiers.

Together with the two 6DR7 tubes used for the initial amplification and driver stages and the 300B power tubes, the result is a fully tube-based amplification chain.

Exceptionally Quiet – Despite the 300B

Headphone listening makes one weakness of many large tube amplifiers especially obvious: even a small amount of hum or background noise can become immediately audible.

Allnic has therefore invested considerable effort in mechanically isolating the tubes. The tube sockets in the signal path are mounted on liquid rubber, while the 300B tubes are additionally stabilised by specially developed dampers. This is intended to significantly reduce susceptibility to microphonics.

“The quietest tube amplifier I have encountered in the last two decades.”
– Kevin Fiske, hi-fi+

For a powerful 300B amplifier, that is a particularly notable verdict – and for headphone use, low noise can be every bit as important as sheer output power.

Not the Typical Warm-Sounding 300B Amplifier

Sonically, the Allnic also departs from many expectations associated with traditional 300B amplifiers.

“The amplifier sounds fast and energetic, both through headphones and speakers.”
– Kevin Fiske, hi-fi+

That is precisely where the HPA-300B becomes particularly interesting. It combines the physical, dimensional presentation of a directly heated triode with a distinctly more modern character: fast, open and dynamic rather than excessively soft or dark.

This makes it especially compelling with highly resolving dynamic and planar magnetic headphones, where the natural tonal qualities of a 300B can be enjoyed without sacrificing precision or attack.

From 10 to 600 Ohms

Allnic specifies an optimal headphone impedance range of 10 to 600 Ω. The HPA-300B is therefore not limited to traditional high-impedance designs.

With a maximum output power of 8 watts, it also offers sufficient reserves for many demanding planar magnetic headphones.

In its review, hi-fi+ used the Allnic with headphones including the Sennheiser HD 650, Audeze LCD-5 and HiFiMAN Susvara – three models with very different amplification requirements.

61-Step Constant Impedance Attenuator

As with the HPA-15000, Allnic equips the HPA-300B with its proprietary 61-step Constant Impedance Attenuator.

Instead of using a conventional potentiometer, this sophisticated volume control maintains a constant impedance throughout its operating range. This helps preserve channel balance, dynamics and spatial definition, even at low listening levels.

This is particularly useful with headphones, where listening often takes place much closer to the lower end of the volume range than in a conventional loudspeaker system.

Four Headphone Outputs

The front panel provides a total of four headphone connections:

• 2 × 4-pin XLR
• 2 × 6.35 mm headphone outputs

This makes the HPA-300B particularly convenient in systems with several high-end headphones and equally suitable for direct comparisons between different models.

Optionally, one of the XLR sockets can be factory-configured as a RAAL Direct Drive output, allowing compatible ultra-low-impedance RAAL ribbon headphones to be driven directly.

Five Analogue Inputs

The HPA-300B is equally generous on the source side. A total of five analogue inputs allow multiple DACs, phono stages or other sources to be connected directly:

• 3 × stereo RCA
• 2 × stereo XLR

Both input selection and volume can also be controlled using the supplied remote control.

A Genuine 300B Loudspeaker Amplifier

Unlike many headphone amplifiers, the HPA-300B does not merely provide an additional line output. Its rear panel features dedicated loudspeaker terminals for 4- and 8-ohm speakers.

This turns the Allnic into a genuine 300B integrated amplifier. In combination with efficient loudspeakers, its 8 watts of Class A power can drive an entire loudspeaker system.

The loudspeaker output can be conveniently muted when the amplifier is used exclusively with headphones.

Allnic Audio HPA-300B – Highlights

• High-end 300B tube headphone and integrated amplifier
• Pure Class A operation
• 2 × 300B power tubes
• 2 × NOS 6DR7 driver tubes
• 1 × NOS 5U4G / 5U4GB rectifier tube
• GZ34 / 5AR4 compatible rectifier alternative
• Choke transformer drive for the 300B output stage
• Fast output transformers specifically developed for headphones
• Mechanically isolated tube sockets to reduce microphonics
• 61-step Constant Impedance Attenuator
• Up to 8 watts of output power
• Optimal headphone impedance range from 10 to 600 Ω
• 2 × 4-pin XLR and 2 × 6.35 mm headphone outputs
• 3 × RCA and 2 × XLR inputs
• 4 Ω and 8 Ω loudspeaker outputs
• Optional RAAL Direct Drive output
• Remote control for volume and input selection

Technical Specifications