Q-tron Audio PA12B 2x25W Push-Pull Tube OTL Power Amplifier

High linearity and low-impedance drive achieved by meticulous Futterman-derived design

The output stage of the PA-12 features a Futterman-based circuit optimized by Q-tron using modern components and analytical technology. The Futterman design, born to drive speakers directly without an output transformer, provides excellent linearity across a wide bandwidth through push-pull operation.
Q-tron has advanced this traditional design, combining proprietary balance adjustments and stabilization techniques to ensure unwavering control and high transparency even under complex speaker loads. This allows accurate reproduction of the finest musical nuances.
Each channel is equipped with two 6C33C tubes, securing a maximum output of 25W. Even at 10W output, the distortion rate is below 0.1%, and at 1W, it achieves an extremely low distortion of 0.01%.

Noise floor below 100 dBA — active noise reduction supporting silence

The PA-12's quiet performance is supported by active noise reduction technology.
The noise floor is below 100 dBA. Hum and power-related noise are thoroughly suppressed, allowing delicate signal transients to emerge beautifully.

Nordic precision design — a fusion of 10mm aluminum chassis and PtP wiring

The main board is built on a high-quality PCB, but the parts that directly affect sound quality are carefully finished with point-to-point wiring by skilled engineers.
Designed throughout to suppress mechanical vibration and unnecessary noise, including a 5kV ceramic solder support and a 10mm thick aluminum chassis. All parts and manufacturing are done in Sweden, ensuring high reliability and long-term durability.

Ideal automatic adjustment - advanced auto bias system

A new standard for high-end OTL amplifiers that combines quietness, power, and naturalness.

Generous driving force and sense of scale

• With a sufficient output of 25W, the PA3B can now drive a wider range of speakers with ease while preserving its characteristic transparent and delicate tone. Even low-efficiency models can be controlled firmly, allowing the music to unfold in a relaxed yet powerful manner. The sense of scale and dynamics has greatly increased, and even large orchestral works show no sign of breakdown.
  

Large-Scale Soundstage Reproduction

• Thanks to the excellent phase characteristics unique to the OTL design, the soundstage expands beautifully.
  With the added output margin, the soundstage is depicted with greater depth, height, and three-dimensionality, which is especially noticeable in larger listening rooms. The sense of openness and spatial clarity is a step above the conventional PA3B.
  

Combination of Silence and High Resolution

• The OTL’s distinctive clarity, where sound emerges smoothly from silence without any roughness, remains intact. With a low noise floor and very high resolution, even subtle nuances hidden deep within recordings clearly come to the forefront. The impressive balance of serenity and high resolution allows the listener to feel the depth of the sound more and more as they listen.
  

Maintaining Musicality

• Even with increased output, the transparency and immediacy of the sound remain unchanged. In fact, the added margin allows the rich midrange resonance to extend more naturally, keeping the PA3B’s characteristic musicality alive. The rich texture unique to tube amplifiers coexists beautifully with the speed and transparency inherent to OTL, which I found particularly appealing.

Purity and Transparency of Sound — The Advantage Unique to OTL

• Even among OTL amplifiers, there are few that convey such a ‘pure sound’ as this one does.
  In addition to the transformerless design, the proprietary distortion and noise elimination circuitry works effectively to thoroughly remove elements that could cloud the sound. The transparency reaches an extreme level, comparable to high-end Class A solid-state amps—sometimes even feeling superior. The exceptionally low noise floor is astonishing, offering outstanding reproduction of delicate signals. Listening during a quiet late-night session, you can almost perceive the breathing of instruments and the subtle air movements in the hall, and the silence is so profound that you can't help but think, 'This is a true reference.' You can also experience the excellent phase characteristics unique to OTL, with extremely sharp sound imaging. The sound stage expands deeply and three-dimensionally, impressing with the precision of the stereo image.
  

Overwhelming Speed and Detail Reproduction

• By completely avoiding DC-blocking capacitors in the signal path, the response speed is incredibly fast. With a rise time of 0.5 μs, the ability to follow instantaneous changes is exceptional, and the sharpness and attack of the sound can hardly be replicated by other types of amplifiers. The high frequencies are full of life; you can even feel the air tension at the exact moment guitar or shamisen strings are plucked.
  Meanwhile, the bass isn't just emphasized in volume but is accurate in pitch and tightly controlled, offering a very tight and well-defined character. There’s no blurriness, and the overall rhythm of the music is cleanly maintained. The detail reproduction is also impressive, bringing out every nuance of the recording, allowing even familiar tracks to reveal new discoveries.
  

Musicality and Speaker Compatibility

• Despite its precision, this amp doesn't have the 'coldness' typical of studio monitors. The music flows naturally, creating a comfortable experience that draws you in, achieving an exceptional balance between musicality and analytical power. It pairs especially well with high-efficiency speakers—the sense of joy when combined with Altec Valencia (100dB) is indescribable.
  Rich harmonics and transparency complement each other, creating an utterly blissful listening experience.
  The 25W per channel output is sufficient and can easily drive speakers with an efficiency of 90dB or higher, but it can be challenging with low-efficiency models like the 82dB-class TAD, which may prevent the amp from demonstrating its full potential.