The Flux Lab Mentor review unit was kindly provided free of charge. I didn’t receive monetary or any other kind of compensation and I don’t use affiliate links. The base price for a single Flux Mentor is $1229 and $1299 with the additional mono input so a dual mono set-up costs $2599. The Flux Mentor is available from here. All orders are dispatched from a warehouse in Poland so EU customers will not have to deal with import fees and tax.
This is the world premiere review of the Flux Lab Acoustics Mentor headphone amplifier.
Flux Lab Acoustics
Flux Lab Acoustics, a Ukrainian firm, specializes in crafting top-notch audio devices. Renowned within the audiophile community, they have an impressive range of successful and acclaimed products, such as the Flux FCN-10 and FA-12 headphone amplifiers. These offerings are highly regarded for their exceptional sound quality and sturdy construction, all while being sold at affordable prices.
The business of Flux Lab Acoustics was severely impacted by the Russian invasion of Ukraine, leading to a halt in production. Fortunately, no team members or their families suffered fatal injuries. With the Russians withdrawing, Flux Lab was able to restart production at their Kharkiv facilities. The Mentor, their latest headphone amplifier, was developed amidst the chaos of war, showcasing the team’s unwavering dedication and resilience.
Flux Mentor Review
The Flux Mentor is a Class-A, dual mono headphone amplifier with many technical innovations, let’s find out more.
Amplifier design
The class A operation of the output stage enables the transmission of low-amplitude signals with utmost precision. The amplifier circuit incorporates J-Fet transistors at the input to produce a rich and seamless sound, while the specially designed bipolar (BJT) transistors at the output ensure the highest fidelity and transparency in high-end audio circuits. With a power supply of 70 volts, the amplifier circuitry guarantees uncompromising dynamic performance, making it suitable for even the most demanding headphones available in the market.
Power supply
The amplifier follows the dual mono principle, featuring separate power supplies and transformers for each channel. Each channel is equipped with four high-capacity capacitors from Cornell Dubilier Electronics, ensuring ample current delivery and minimal output impedance.
Custom power transformers are employed in the power supply to minimize dissipation field and noise, allowing the amplifier circuit to operate silently even with high-sensitivity headphones. Additionally, Flux has integrated an Ultra Pure Oxygen Free Copper (UP-OFC) power cable shielded by Neotech from the AC inlet socket to the power transformers.
Volume controller
The volume adjustment is achieved through a relay attenuator featuring 64 steps. Panasonic fast signal relays with minimal contact resistance are utilized in the control circuit. The analog signal is directed to the relay attenuator positioned near the input ports, while control is managed solely by the ALPS variable potentiometer from the Blue Velvet series.
Improved heat-sinks
Class-A generates a significant amount of heat that requires efficient dissipation. To address this issue, Flux has enhanced the heat sink design. The amplifier circuitry is quickly primed for operation, delivering its optimal sound quality within just 15 minutes. Furthermore, by strategically positioning the heat sink beneath certain PCB components, the amplifier circuitry is able to power up more rapidly and maintain superior thermal stability throughout the entire circuit.
The mono input module
The Flux Mentor offers a unique feature that enables the synchronization of two amplifier units in a dual mono configuration, providing an increased power reserve. Both channels of the amplifier function in a fully balanced mode. By designating one unit as the master and the other as the slave, you can easily set up the synchronization. This system also grants you the ability to manage the second amplifier’s operation, ensuring that when the master unit is powered on, the second unit follows suit automatically.
The dual mono Mentor, when set in mono mode, can deliver an impressive 33.5W RMS per channel at 32Ω and 6.4W RMS per channel at 300Ω, offering substantial power output suitable for driving every headphone in existence . You have the option to choose the Mentor with or without the mono module.
FLUX guarantees an absolutely identical volume level between the two units, even if the second unit is purchased much later. The differences may be primarily due to the tone of the front panels, as there are slight differences from batch to batch.
Components and PCB
The circuitry boasts top-notch components such as Takman resistors (Rex and Rey series), high-end Vishay VAR series uncased audio resistors, PRP resistors, as well as capacitors from Cornell Dubilier, Nichicon, Wima, and Epcos. The internal PCB showcases exceptional workmanship with predominantly through-hole components, showcasing superb soldering, cabling, and assembly quality.
Optional remote control
The Mentor offers convenient remote control capabilities for adjusting volume and muting/unmuting functions. This optional, high-quality remote control is crafted from durable aluminum and is available for an additional $50. While it could have been included as a standard feature, its separate purchase allows cost savings for individuals who do not require it.
The volume can be adjusted using the remote control, eliminating the need to physically turn the volume knob. Whenever the knob is touched, the volume instantly returns to its original position.
Optional power cable upgrade
The designer recommends using a high-quality power cable to maximize the performance of the Mentor. You have the option to choose your preferred brand or opt for the Flux Lab custom-made power cable. This cable is constructed with an NEP-5002 conductor from Neotech, featuring thick conductors (0.42mm) of ultra-pure oxygen-free copper (UP-OFC). The ground conductor has a smaller cross-section (1.43mm), resulting in a slim and flexible design for enhanced user experience. With an internal aluminum foil shield and a drain wire, the cable offers complete protection from external electromagnetic radiation. Additionally, filling the free volume with synthetic fiber ensures comfortable flexibility and a “memory” effect, allowing easy positioning and maintenance in the desired configuration.
Each cable is meticulously hand-crafted in the Flux Lab workshop and comes equipped with high-quality TTAF 93047/048 connectors featuring gold-plated brass and copper contact groups. The cable is 1.8 meters (6 feet) in length and can be purchased as an additional $100 when ordering the Mentor.
Aesthetics and build quality
The Mentor’s chassis is constructed using a sleek black metal sheet, providing a durable and stylish foundation. Its front panel and the impressively robust volume knob, both custom-made, are crafted from a single piece of solid aluminum alloy. These components are meticulously painted with a high-quality finish, resulting in a remarkably smooth surface. You can choose between two color options: titanium gray and coal black.
To ensure stability and minimize vibrations, the chassis is equipped with four anti-vibration feet as a standard feature.
One notable aspect is the chassis’s unique shape, measuring 342x397x82mm. This design choice makes it deeper and narrower than the industry standard, which may pose challenges when positioning it alongside or beneath other audio components.
Interface and operation
The Flux Mentor is a headphone amplifier design that does not include a preamplifier output function or digital inputs. It offers balanced XLR and single ended RCA line inputs at the rear of the unit, allowing for simultaneous connection of both inputs with the ability to switch between them using the front switch. Additionally, the back panel includes the AC input and an optional synchronization interface.
On the minimalist front panel, you will find power on/off, input selection, and gain switches on the left side, the imposing volume knob in the center, and two headphone outputs on the right side. The first headphone output combines a 6.35mm jack and 3-pin XLR for mono mode, while the second output features a 4-pin XLR connection.
Power output
The Mentor boasts an impressive power output of 11.2W (32Ω) and 1.6W (300Ω) RMS per channel, making it one of the most robust amplifiers available. To accommodate various headphone loads, Flux has integrated three gain settings (low/14dB, medium/20dB, and high/25.3dB) that users can easily switch between from the front panel.
The stepped attenuator is meticulously calibrated for precise adjustments with each incremental “click”, maintaining a perfect balance between being too loud and too quiet. To assess the power output and volume range of the Mentor, the Focal Clear Mg takes around 21 steps to transition from silence to fairly loud at a low gain setting, whereas the HIFIMAN Susvara requires 30 steps at high gain. Nevertheless, volume levels alone do not tell the whole story; what truly sets the Mentor apart is its capability to drive the Susvara with outstanding dynamic range, precise control, strong grip, and an abundance of headroom.
The Mentor boasts impressive power, yet its finely-tuned low gain setting allows it to effectively drive even the most sensitive earphones without reaching excessive volume too quickly. For instance, the FiiO FX15 requires 18 steps to reach a comfortably loud level.
The Flux Mentor distinguishes itself from other Class-A amplifiers by maintaining a cool temperature, with only a mild warmth felt under the bottom of the chassis. Even when subjected to demanding conditions, the rest of the chassis remains cool and unaffected.
The Mentor was left playing music for more than 150 hours in order to leave time for the bid capacitors and other components to settle down. The Flux Mentor was tested with the Flux/Neotech power upgrade cable. All headphone cables are made by Lavricables.
Listening impressions
The sound of silence
The Mentor remains completely silent, devoid of any faint background hiss, even when paired with highly sensitive earphones. Its pitch black background allows the most delicate sonic elements to effortlessly emerge and come to the forefront of the recording, resulting in a pure and organic sound that is rich in detail without ever sounding clinical or lifeless. The silence that accompanies the Mentor’s sonic performance is not only audible but also remarkably advantageous, creating an uncanny and haunting tranquility that is typically found only in the finest “high end” amplifiers.
Let’s discuss sources
The Flux Mentor boasts exceptional transparency and remarkable scalability, making it a top-tier amplifier in its class. Its fidelity is akin to a mirror, requiring only the finest sources to truly showcase its full potential. Rest assured, the Mentor will never hinder the performance of your system, consistently bringing out the best in your source and headphones by accentuating their distinct sonic qualities. Conversely, subpar sources and headphones may fall short in fully utilizing the Mentor’s capabilities.
I commenced my listening sessions by relying on reputable mid-range sources such as the Aune X8 XVIII and the Volumio Primo (v2). However, as I progressed, I couldn’t help but feel that the Mentor had the potential to deliver even more impressive results.
I decided to make a change and switch to the HIFIMAN Serenade, the Denafrips Pontus II, and the Lab 12 dac1 reference (custom edition). All three of these devices performed exceptionally well and exceeded their price expectations. Finally, everything fell into place and this combination revealed all the remarkable sonic qualities of the Flux Mentor. Alternatively, one could say that the Mentor showcased the exceptional sonic qualities of the sources. Regardless, I am confident that if I had even better sources, the Mentor would have sounded even more impressive.
However, it is important to note that the Mentor is not an elitist amplifier. It can be enjoyed with your favorite sources, taking you on an endless musical journey that may eventually lead you to an upgrade path.
Let’s discuss headphones
The Mentor eliminates any concerns regarding headphone matching, as it seamlessly pairs with a wide range of headphones, faithfully reproducing their unique sound signature with remarkable accuracy. I have had the pleasure of experiencing exceptional audio quality with various headphones, including the Sennheiser HD660S2, HIFIMAN Arya Organic, Meze Elite, and HIFIMAN Susvara. The Mentor consistently delivers outstanding performance, with the quality improving in tandem with higher-end headphones.
Let’s discuss sound
One might question whether the Flux Mentor is comparable to a “wire with gain” amplifier. However, the Mentor is actually the complete opposite. It is an amplifier that has been meticulously adjusted by ear to achieve a perfect balance of transparency, fidelity, and musicality. Through months of careful tuning, the Mentor has developed a unique sound signature that is smooth, effortless, and immersive, while still maintaining a natural and communicative quality without drawing attention to itself.
Unlike other amplifiers that may initially impress with flashy and powerful performances, the Mentor prioritizes precision and tranquility. It does not rely on short-lived pyrotechnics that may captivate at first, but ultimately fail to convey the true essence of the music.
The Mentor embodies a subtle influence, an experienced and refined amplifier that delicately harmonizes technical precision and musicality in the precise proportions required to render your music with utmost realism. Simultaneously, it upholds the sonic attributes of the original source and the headphones employed.
This amplifier exudes dynamism and impact, yet not in an aggressive manner. It operates with swiftness, accuracy, and precision, offering crystalline clarity and a commanding presence across the entire frequency spectrum. However, it accomplishes all of this with an air of aristocratic politeness. The Mentor is not characterized by rawness or boldness; rather, it is an intellectual amplifier that engages your mind and heart, rather than stimulating primal instincts.
More sound impressions
The Mentor’s resolution and refinement are truly remarkable, particularly in the treble where it delivers a silky smooth and ethereal sound without compromising on extension and energy. The mid-range is expansive and well-defined, with a natural voicing that brings out the best in every instrument. The bass, on the other hand, exhibits impressive layering and definition. The timbre is exceptionally natural and realistic, capturing the organic essence of every note. Whether it’s acoustic music or any other genre, the Mentor excels in reproducing lifelike sound and possesses the technical prowess to handle all types of music.
The sound is velvety and subtly warm, yet not soft or gloomy. The melodic music is rich in vibrant harmonies and nuances, reminiscent of a blooming meadow teeming with spring blossoms and countless butterflies. The consistency is substantial and palpable, with each individual note resonating with weight and depth. The amplifier showcases impeccable precision, allowing the music to gracefully dissipate in a truly organic fashion – neither hurried nor sluggish. The duration from the inception to the conclusion of a note mirrors the original recording with utmost accuracy.
Soundstage
The Mentor offers a soundstage that is deep and expansive in a natural manner, devoid of any artificial widening or deepening. Its separation capabilities are outstanding, excelling in both vertical and horizontal planes, providing top-notch positioning accuracy and imaging. The overall presentation is grand and holographic, creating an immersive listening experience. Large symphonic works are particularly impressive, with the listener feeling as though they are seated a few rows behind the conductor, fully immersed in the symphony orchestra’s grandeur. The Mentor also excels in reproducing ambient information captured in high-quality recordings, enhancing the overall realism of the listening experience.
At this point, I must say, I truly appreciated the recent recording of Handel’s opera, Alcina. The Mentor, paired with the Lab 12 DAC and the Meze Elite, captured the true spirit of the performance, making me feel as though I was present at the event.
The competition
There are several other solid state amplifiers that I have evaluated and should be considered as potential alternatives to the Flux Mentor. Notably, the Violectric V222, V340, and V550 are worth mentioning. In terms of sound quality, the Mentor shares more similarities with the flagship V550 compared to the other two models. The V222 offers a warmer, tube-like character, but it falls short in terms of precision, resolution, and transparency when compared to the Mentor. On the other hand, the V340 comes close but still doesn’t quite match up to the level of the V550.
The fact remains that the Violectric V550 and the Flux Mentor possess numerous shared attributes when it comes to their transparency, precision, and mirror-like fidelity. Furthermore, both exhibit a musical and captivating sound, devoid of any clinical or sterile qualities, despite their flagship technical prowess.
The Flux Mentor provides a calmer and more polite amplification compared to the Violectric V550, which is known for its muscular brutality and raw power. The sound from the Mentor is more sophisticated and well-mannered, offering a delightful Class-A timbre that enhances the organic and natural quality of the music. While the V550 is more impactful on the low-end and energetic in the treble, it lacks the fluidity, realism, and holographic sound that the Mentor delivers, making it a more immersive listening experience overall.
Other, non sound related, differences are that the Violectric V550 is also a premium balanced preamplifier and features an all aluminum chassis. However, it comes at a higher price point compared to the Flux Mentor. Furthermore to access a stepped attenuator, which is a standard feature in the Flux Mentor, you would need to invest further in upgrading to the V550 PRO.
In the end
Some incredible human creations have been achieved amidst times of conflict. The Flux Mentor stands out as a remarkable creation, showcasing a level of maturity and sophistication that sets it apart as a masterpiece in the world of amplifiers. Crafted with precision and care, this amplifier contains all the necessary components in perfect balance to deliver an exceptional sonic experience. With the introduction of the Flux Mentor, high-end quality has become more accessible than ever before. Flux Lab Acoustics has truly outdone themselves with this end-game solid state amplifier, offering a product that eliminates the need for future upgrades. Undoubtedly, the Flux Mentor reigns as the most cost-effective high-end headphone amplifier available, boasting an unparalleled value for money and securing its position as one of the top bargains in the audio industry.
Copyright – Petros Laskis 2024.
+ Masterclass fidelity and transparency
+ Exceptionally resolving and refined
+ Crystalline clarity
+ Balanced and natural
+ Impactful and dynamic
+ Outstanding technicalities
+ Captivating and harmonious
+ Immersive and very open soundstage
+ Natural and organic timbre
+ Super powerful
+ Three gain settings
+ Completely quiet
+ Dual mono power supply
+ Convenient remote functionality
+ Dual monoblock operation with two units
+ Superior craftsmanship and aesthetics
- Not that muscular and visceral textures
- The remote control is optional
- No preamplifier output
- The dimensions do not adhere to the industry standard
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