There's nothing like Enleum's HPA-23RM on the market. As if being one of the only current-source headphone amplifiers on the market isn't enough, HPA-23RM also operates without negative feedback and features a relay-based variable gain volume control in a portable, battery-powered package.

Chae Soo-in was never one to design something to please every member of the masses, but the HPA-23RM is possibly the closest he's come to doing so for Head-Fi.

Soundnews handed it their unequivocal Gold Award. "Compaction without sonic degradation is really hard work" said 6Moons but Enleum aced it! Headphone Guru says it packs serious punch driving Susvara. Part-Time Audiophile give it their "highest recommendation" as a Reviewers Choice. The Ear says it's "in a league of its own". hear.audio feels they are well worth their premiums.

Enleum's current-source technology infuses musical notes and textures with microdynamic zeal and a charged portrayal, associated with the finest Class A designs. It offers ample extension at the frequency extremes and, at the macrodynamic level, delivers scale and stage.

Flat impedance headphones such as HiFiMANs, HEDD Audio's Heddphone 2, the ZMF Headphones Caldera and Final Audio's D7000 will thank Enleum. HPA-23RM is the first resurgence of a current-source amplifier since the days Bakoon International rebranded as Enleum. [See Product Desc. For More]

And in addition to the HPA-23RM's current-source output, Chae has designed a completely separate circuit and output that functions as the kind of voltage source found in 99 per cent of other amps, intended for use with your Focals, Fostexs and earphones.

In this portable Enleum are therefore two entirely different headphone outputs that allow you to mix and match between what sounds best with your transducers, and act as an empowerer for all your flagship sources.

3.5mm or RCA line-in from any of Cayin Audio's N7 and HiBy Music's RS6 or RS8, for fireworks at your desktop or on your travels.

But if you are familiar with Enleum and Bakoon, you'll immediately gravitate toward its specialised trademark: the current-source output on 1/4". While there may be temptations to draw quick and easy comparisons to current-mode amplification found in products like Mass-Kobo and Questyle Audio, Enleum's current-source amplification is entirely unique and mutually contradictory.

Working in a way that keeps output current levels constant at all times, even as impedance and voltage fluctuate, the HPA-23RM aims to address a perennial problem – that headphones and earphones induce distortion in amplifiers because they are not simple resistive loads, but rather have complex, frequency-dependent, inductive and capacitive components.

However, with the HPA-23RM aiming to eliminate distortion by driving headphones as a constant current source, you experience much greater linearity, hearing an output that faithfully reproduces what was received at the source: the input. Reduction in the effects of backward electromotive force from headphone drivers results in a cleaner sound.

With greater linearity and a more accurate final product, negative feedback, typically employed to correct glaring errors, can be eliminated in the HPA-23RM. Enleum's circuit transmits the signal faster and can be kept simpler with far less transient intermodulation distortion arising from feedback.

Single-ended operation emphasises even-order harmonics over odd ones, granting a natural portrayal of music that never once sounds artificial.

Enleum's JET2 sliding bias scheme intelligently monitors the operating conditions of the discrete devices that make up HPA-23RM's circuit/s, ensuring that transistors operate linearly biased against their current sources in single-ended operation, without generating excessive heat from full Class A. This is a thoughtful addition for a portable product.

Listeners can enjoy these innovations with both the current-source and 3.5mm voltage-source outputs on the HPA-23RM. If you aren't into art nouveau and aren't ready to embrace Enleum's current-source output, stick with the conventional voltage-source output that has defined gain amplifiers for nearly all of history.

Your ears would certainly benefit from experimenting with either circuit, each completely separate from the other. Some of your gear would certainly thank you, especially those that gravitate towards the low output impedance typical of a voltage source, like Focal's Utopia and IEMs.

These transducers also particularly crave a low noise floor. HPA-23RM's precise relay-based discrete resistor volume control provides just that – but not in the way you think.

Rather than attenuating signal levels, it's a variable gain volume control that leaves the fragile input signal untouched. Instead, it changes the total amount of gain that's applied to the signal, with only the necessary amount used and never incurring the consequence of detrimental noise from an excess.

Variable gain is possible only because HPA-23RM is a zero-feedback design. Enleum's volume control is ideal for preserving the signal-to-noise ratio and the true dynamic range of your music. And a fully-regulated 18650 battery power supply, operating at 1.2MHz, similarly ensures a quiet performance.

HPA-23RM is thus a tour de force that demonstrates how mature Enleum has become, offering users abundant choices between two completely different circuits in one chassis – each on par with the other in terms of quality, with only synergy defining your final choice.

Look up all of Enleum's gear here, or view our other amplifiers here.

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