Allnic Audio HPA-10000 XL OTL/OCL

High-End Class A Tube Headphone Amplifier and Line Stage with True OTL/OCL Architecture and up to 10 Watts of Output Power

The Allnic Audio HPA-10000 XL is one of those amplifiers whose technical architecture immediately explains why it exists. Allnic completely eliminates two components from the output stage that are almost taken for granted in conventional tube amplifiers: output transformers and output capacitors.

The result is a true OTL/OCL circuit – Output Transformer-Less and Output Capacitor-Less. There are therefore no transformers or large coupling capacitors between the output tubes and the connected headphones that could impose their own electrical characteristics on the signal.

Allnic combines this purist concept with an exceptionally powerful Class A output stage. With up to 10 watts of output power, the HPA-10000 XL is not limited to traditional dynamic headphones, but also has sufficient reserves for many demanding planar magnetic designs.

OTL and OCL – No Detour Between Tubes and Headphones

Tubes naturally operate at high voltages and comparatively high impedances. In a conventional tube amplifier, an output transformer is therefore usually used to match the tube circuit to the much lower impedance of a pair of headphones. Alternatively, large output capacitors can be used to block DC.

Both solutions can work extremely well, but inevitably influence the signal. Transformers have finite bandwidth, while coupling capacitors exhibit electrical properties that vary with frequency and load.

The HPA-10000 XL removes both elements from the output signal path. The output tubes are directly coupled to the headphone output. The objective is an exceptionally immediate transfer of the signal, with high transparency, fine microdynamics, natural decay and minimal sonic coloration.

Floating Power Supply Instead of an Output Capacitor

Eliminating the output capacitor places considerable demands on the circuit, as this component would normally prevent DC voltage from reaching the connected headphones.

Allnic solves this problem with a floating power supply architecture. The circuit is designed so that problematic DC voltage should not arise at the output in the first place.

This allows Allnic to retain the advantages of a directly coupled OCL output without inserting a large capacitor into the signal path.

Active Balanced Positive/Negative Cancellation

The HPA-10000 XL uses a sophisticated SEPP – Single-Ended Push-Pull architecture. To maintain precise balance between the upper and lower output tubes, Allnic employs an active Positive/Negative Feedback Cancellation system.

Two NOS 7258 tubes play a central role in this active regulation system. Together with two NOS E180CC tubes and a total of eight 6C19P output tubes, they form an unusually elaborate tube circuit with high current capability and extremely fast control.

The objective is not the stereotypical soft tube sound, but rather a combination of tube harmonics and spatial naturalness with speed, control and an exceptionally neutral output.

Eight Output Tubes and 10 Watts in Class A

A total of eight 6C19P power triodes form the output stage of the HPA-10000 XL. They operate in pure Class A and allow the amplifier to deliver up to 10 watts.

For an OTL/OCL tube amplifier, this is an unusually high level of output power. Allnic specifies an optimal headphone impedance range of 15 to 600 Ω.

This gives the HPA-10000 XL an exceptionally broad operating range, from traditional high-impedance dynamic headphones to considerably more demanding planar magnetic models. Even power-hungry headphones can therefore be driven with substantial reserves.

Tube Sound – Without Soft Focus

Anyone who automatically expects a tube amplifier to sound warm, slow or deliberately romanticised will only partially understand the concept behind the HPA-10000 XL.

The OTL/OCL architecture is specifically designed to eliminate additional output components and their sonic influence. The Allnic therefore aims to combine the dimensionality and harmonic naturalness of tubes with the speed and openness of an exceptionally direct signal path.

“Exceptionally natural and engaging.”
– AudioKey Reviews

AudioKey Reviews even describes its spatial presentation as electrostatic-like, while retaining the weight, substance and dynamics associated with dynamic and planar magnetic headphones.

A Soundstage with Exceptional Depth

According to several listening impressions, one of the most striking characteristics of the HPA-10000 XL is not merely its resolution, but its spatial presentation.

Instruments are not simply placed left and right. The Allnic places great emphasis on depth layering, physical body and the spatial separation of individual musicians – qualities that contribute significantly to the perceived naturalness of excellent open-back headphones.

“I feel like I’m hearing more colors in the music than before.”
– Marc Phillips

This is less about introducing artificial coloration and more about making fine differences in timbre, dynamics and texture more clearly audible.

Surprisingly Uncompromising Bass

One common preconception about OTL tube amplifiers concerns bass performance. Without an output transformer or large coupling capacitor, one might expect less control or less extension in the low frequencies.

This is precisely where the HPA-10000 XL becomes one of the more interesting implementations of the concept. The high current capability of its eight output triodes allows it to produce fast, controlled and finely differentiated bass.

AudioKey Reviews accordingly describes its low-frequency performance as tight, agile and extremely fast – qualities that can be particularly impressive with large planar magnetic headphones.

61-Step Constant Impedance Attenuator

For volume control, Allnic uses the same fundamental concept found in its high-end line-stage preamplifiers: the 61-step Constant Impedance Attenuator.

It uses only a single silver contact in the signal path and maintains a constant impedance throughout the entire adjustment range. Allnic specifies virtually no channel imbalance across the individual volume steps.

Precise volume control is particularly important with headphones, where even very small differences between the left and right channels can shift the perceived position of a central vocal image.

Four Headphone Outputs

The HPA-10000 XL is also unusually generous in terms of connectivity. The front panel provides a total of four headphone outputs:

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

Several high-end headphones can therefore remain connected at the same time, which is convenient both in a private system and when directly comparing different models.

Five Analogue Inputs

On the input side, the Allnic offers a total of five analogue connections:

• 3 × stereo RCA
• 2 × stereo XLR

A DAC, phono stage and additional analogue sources can therefore remain permanently connected. Input selection and volume can be controlled conveniently using the supplied remote control.

Also a High-End OTL/OCL Preamplifier

The HPA-10000 XL is more than a headphone amplifier. Via its rear RCA pre-out, its OTL/OCL circuit can also be used as a fully fledged line stage for a separate power amplifier.

With an output impedance of just 20 Ω, the line output is exceptionally low impedance and can be paired with a wide variety of power amplifiers.

The line-stage output provides +16 dB of gain, while the headphone amplifier itself operates with +28 dB.

The HPA-10000 XL can therefore become the centrepiece of a complete analogue system, allowing both headphones and a loudspeaker setup to benefit from the same uncompromising tube line stage.

Allnic Audio HPA-10000 XL – Highlights

• High-end tube headphone amplifier and line stage
• True OTL/OCL architecture
• No output transformers in the standard signal path
• No output capacitors in the standard signal path
• Floating power supply architecture
• SEPP – Single-Ended Push-Pull topology
• Active Balanced Positive/Negative Feedback Cancellation
• Pure Class A operation
• 8 × NOS 6C19P output tubes
• 2 × NOS E180CC second-stage tubes
• 2 × NOS 7258 first-stage and control tubes
• Up to 10 watts of output power
• Optimised for headphones from 15 to 600 Ω
• 61-step Constant Impedance Attenuator
• 2 × 4-pin XLR headphone outputs
• 2 × 6.35 mm headphone outputs
• 3 × RCA and 2 × XLR inputs
• RCA line-stage output with just 20 Ω output impedance
• Remote-controlled volume and input selection

Technical Specifications