Q-tron Audio PA34B 80W High-End OTL Mono Power Amplifier

Q-tron PA34B – 80W OTL power amplifier with plenty of room for high impedance loads

The PA34B is a monoblock OTL power amplifier that is based on Q-tron's flagship PA12B and greatly expands its output and current supply capabilities. The output stage is equipped with four 6C33C vacuum tubes, which have approximately twice the current capability of the PA12B, providing high braking power even for inefficient speakers and large floor-standing models. Although it is a tube amplifier, it has enough output of 80W at 8Ω and 60W at 4Ω, so you can use it in combination with modern speakers.
By eliminating the output transformer due to the OTL (Output Transformer Less) design, there is no distortion or bandwidth limitation caused by the magnetic properties of the transformer, and the sound rise is extremely fast, and direct and highly transparent reproduction is possible. The Futterman circuit is optimized for modern use in a push-pull configuration, and the output impedance is limited to a range of 0.2 to 1.5 Ω, ensuring stable driving even for heavily loaded speakers.

 

Redesigned Futterman circuit for both transparency and braking power

The output stage of the PA34B uses a Futterman OTL circuit with Q-tron's proprietary tuning. In order to maintain a well-balanced push-pull operation without transformers, 6N6P-I is used for the amplification stage and 6N2n-EB for the first stage, and the configuration is designed to achieve both linearity and bandwidth.
It operates extremely cleanly in the micro-signal range around 2 W and maintains low distortion close to the measurement limit. Even if the output is further increased to reach a practical output range of around 25W, the increase in distortion is kept very small, and the energy rises smoothly without losing the clarity and density of the tone. Despite not relying on excessive negative feedback, this linearity is maintained due to the accuracy and stability of the circuit itself.

Active noise cancellation for quietness and stability

PA34B is also very particular about noise countermeasures. The power supply design with active noise cancellation technology ensures that hum and noise levels are managed at very low values of -100dBA or less. Because the background is not muddy and naturally spreads to the atmosphere behind the sound field, the reproduction of classical whole tones and ambiences is particularly highly evaluated.

Large PCB and PtP wiring, 10mm thick aluminum chassis create a sense of tranquility and stability

Drive capability to handle complex speaker loads with plenty of room

Overwhelming driving power and clear sound field expression unique to OTL