Q-tron Audio PA12B 2x25W push-pull tube OTL power amplifier

Q-tron's OTL (Output Transformer Less) amplifiers provide clearer and more expansive sound quality than other tube amplifiers. By eliminating the output transformer required by normal tube amplifiers, the distortion and frequency response limitations caused by the transformer are avoided, resulting in improved sound clarity and response. In particular, the output stage is configured in a push-pull arrangement, and the Futterman circuit, uniquely designed to achieve low impedance without the use of a transformer, provides low output impedance and excellent balance. It also features active noise canceling technology to keep noise below 100 dBA and a design that achieves very low distortion without excessive feedback. In addition, the minimal use of vacuum tubes has proven to be highly reliable and long-lasting. All parts are designed and manufactured in Sweden, and the use of high-quality components ensures high performance over the long term.

With a unique driver circuit that reduces distortion to one-tenth that of other OTL amplifiers, the PA12 is an OTL amplifier with two 6C33C tubes on each channel. This unique driver circuit allows for an output of 25 W. Even at 10 W output, the distortion ratio is less than 0.1%, a very good figure for a tube amplifier. The distortion rate at 1W is even lower at 0.01%, and active noise reduction technology keeps hum and noise to an extremely low level.

The amplifier is largely built on a large PCB, but point-to-point (PtP) technology is used for critical components: ceramic solder supports capable of withstanding 5 kV are used, and the chassis is made of 10 mm thick aluminum, providing excellent mechanical stability and completely eliminating noise caused by vibration. noise due to vibration is completely eliminated.

The Q-tron PA-12 is a revolutionary push-pull tube amplifier design that redefines the possibilities of OTL amplifiers. In addition to the reverse-phase Futterman circuit, the PA-12 employs a unique distortion and noise elimination circuit to achieve a pure and transparent sound never before achieved. It offers sound quality comparable to Class A amplifiers and performs so well that it is truly beyond their realm.
The PA-12's appeal lies in its outstanding textural purity and rich tone, bringing out the essence of the 6C33C power triode, with high frequencies shimmering with life-like clarity and low frequencies powerfully expressed while maintaining extremely accurate pitch control. Unlike conventional tube amplifiers, it avoids the problem of crossover distortion, providing a deep soundstage and a three-dimensional sound image.
Another notable feature of the PA-12 is its speed of response to transients (instantaneous sound changes) and the subtlety of its high frequency range. Because there are no DC blocking capacitors in the signal path, natural, organic detail is reproduced with complete control. This means that the bass line is also very clear and conveyed with great definition. Every minute nuance of music is captured and every detail of any recording is resolved, providing a listening experience that is both inspiring and technically superior.
The PA-12 is a true reference grade amplifier with a very low noise floor and extremely accurate reproduction of low-level detail. It captures the essence of the music and delivers a sound of superior transparency and clarity, eliminating extraneous second- and third-order harmonic distortion.
For those seeking the sonic purity of a tube amplifier, but with the transparency and resolution of the best solid-state designs, the Q-tron PA-12 is definitely a top-class choice. 25W/ch output is suitable for any system, and this amplifier is a true game changer, It demonstrates the true potential of OTL technology and delivers the musicality and precision that audiophiles demand. Highly recommended for all who wish to take their listening experience to a new level. *"*"Enjoy The Music" reference

The amplifier consists of 11 tubes: 2 x 6H6Pi, 5 x 6H2n-EB, and 4 x 6C33C. The miniature tubes are generally spheres similar to 12BH7A and 12AX7. The output tubes were originally designed for regulators and are powerfully large. It has three horns on its head. The power switch on the front panel is pushed in, and after 1.5 seconds a light click of a relay is heard, and the current in the large toroidal transformer slowly ramps up. 90 seconds later a second click is heard, and plate voltage is added. After another 45 seconds, the speaker short circuit is opened and the music is ready to be heard. At this point, the edge of the switch lights up green for the first time, and DC leakage is also monitored to protect the valuable speaker. Note that if the power is turned on without the speakers connected, the protection circuit will be activated. The 6C33C is a ball that originally took 10 minutes to stabilize due to its specifications, so it will take at least 30 minutes for the sound to stabilize. The sound we auditioned was astonishing. Whether classical or jazz, the realism was amazing. No matter what sound was played, it was really stable even in transient areas. The mid and low frequencies have just the right amount of fullness and feel, with a nice sense of spaciousness. I was also impressed with the proper production of difficult guitar and shamisen bursts, as well as the high frequency range of the trumpet. The rise time of 0.5 microseconds was probably a contributing factor.

The sound is precise, but it is not the kind of monitor-like sound you would hear in a professional studio. The Valencia from Altec, which has a high efficiency of 100dB, was used for the listening test. I have used a number of amplifiers up to now, starting with the Yamaha B1 and the McIntosh MC240, but this time I thought the sound from the Q-Tron was the best I had ever heard, and listening to music with these speakers brought me a sense of happiness. It must have been a good match. However, when I listened to music with TAD MEs (1 efficiency is 82dB in 4 ohm equivalent), which have a low efficiency and half the impedance, I did not feel such a sense of happiness. Of course, it is still a good power amplifier for music reproduction. The output power of this OTL amp is 25W, so it may sound a little insufficient when played with low-power speakers. However, speakers with a power level of 90 dB or higher will be loud enough. Both balanced and unbalanced inputs can be selected.

This amp has broken the preconceived notion of what a good amp should sound like. It taught me that there are still things in the world that I do not know. *See "Radio Technology