Aurorasound PADA-300B Mono Block Amplifiers

Shinobu Karaki-san's latest masterpiece - the PADA-300B hybrid, push-pull, mono block amplifiers utilizing replicas of the original WE300B valves with an output of 28 Watts per channel. 

Design Philosophy
Conventional hybrid power amplifiers are constructed using  vacuum tubes in the front-end and transistors for the output stage, the transistors doing the power amplification with the tubes just adding a flavor of the classic tube sound.

However, the PADA-300B is designed in the opposite way – the transistors in the front-end and the tubes for the output. The PADA-300B design leverages the transistors to achieve low distortion, high SNR and wide frequency range, and then utilizes  an inter-stage transformer to drive the output tubes. The inter-stage transformer matches the signal level and supplies the voltage difference between the transistors and tubes. This construction makes optimum use of both the advantages of transistor performance as well as the warm tube sound.

Noise Prevention and Control
Thanks to the excellent linearity of the 300B tubes and Lundahl transformers the PADA amplifier has no negative feedback loop. The tube filament is driven by AC voltage. In many of today’s conventional amplifiers, DC filaments driven by high-current diode devices is used because of its low cost, which often results in low hum noises. DC-driven filaments have other disadvantages, such as unevenness of electron emission in the filament wire due to its resistance factor, which can  damage tubes in long term use. PADA-300B AC drive technique cancels hum noise thanks to its push-pull design and simple center adjustment by its pod trimmer. AC is by far the best method for achieving  optimum performance from 300B tubes.

Self-Biasing
The PADA-300B employs self-bias methodology for operating the tubes, providing long-term stability. The user can change to different brands of 300B tubes by simply plugging them in - no need to re-adjust bias current with a monitoring meter. Self-biasing circuits usually use electrolytic capacitors due to need of large capacitance and small footprints. The PADA-300B, however, uses highly reliable precision polypropylene film capacitors, taking advantage of their superior high frequency response and longer lifetime in high temperatures.

Front End Circuitry
The PADA-300B’s frond-end circuit utilizes NEC and Toshiba Japanese transistors that were developed especially for audio applications from 1970-1980, the golden age of analog audio. Those transistors have been discontinued due to lack of demand in the digital era, but have excellent audio performance compared to the current chip-sized transistors made in China. Aurorasound has a large quantity of new-old-stock of those Japanese transistors from the 70’s and utilizes them in all Aurorasound products.

Power Supply
The PADA-300B’s power supply section has independent regulators for both the front-end and output stage. The front-end regulator Is the same high quality regulator as the Aurorasound VIDA’s, which ensures stability and low noise. The output stage regulator uses super-low-noise silicon carbide Schtokky diodes with large size film capacitors instead of common electrolytic capacitors, once again taking advantage of their superior high frequency response and longer lifetime in high temperatures as in the self-biasing components.

Output Stage
In general, when music plays in fortissimo (very loud) or sequential percussive phrases, common output stages consume a large amount of current power, causing the front-end to suffer. However, PADA-300B system of independent regulators prevents this from happening, managing dynamics extremely well.

Chassis
The chassis consists of 25mm thick solid oiled Rosewood, hand made by a woodworking artisan in Japan’s Shizuoka prefecture, home of Mount Fuji. This rosewood is used for finger boards and sides of acoustic guitars, in which it provides a very robust foundation to support the guitar top board and strings. The effect of the rosewood on the PADA-300B’s is the same as that of the guitar construction. The top of the PADA-300B is made of 4mm thick solid aluminum, a completely anti-magnetic material.

 - Output stage, 300B tubes push-pull 28W@8ohm
 - Front-end, made in Japan discrete transistors
 - Hybrid construction combined by inter-stage transformer
 - No negative feedback loop in total amplifier
 - Lundahl output transformer
 - Solid rosewood body with oil finish
 - Large size EI core power transformer, and very low noise high stability independent power supply section for front-end and output stage
 - Bonnet cover included

 - Input: RCA or XLR balanced
 - Input impedance: 56kΩ (RCA/XLR)
 - Output power: 28W, 8Ω load
 - Signal sensitivity: 400mV/RCA, 800mV/XLR, max power
 - Frequency response: 20Hz – 45kH, +0db/-3dB
 - THD+N: 0.08%  A-weighted
 - Residential noise: less than 0.09mV A-weighted
 - Functions: RCA/XLR input selector, MUTE Switch
 - Vacuum tubes: PSVANE WE-300B
 - Size: W310 xD480 xH248mm with bonnet cover (each mono block)
 - Weight: 19.8kg (each mono block)
 - AC power supply: AC115V or AC220V
 - Power consumption: 180W (each mono block)