Stereo Sound Magazine 2020 Winter Vol.213

Aurorasound PADA-300B review
Hybrid Power Amplifier with semiconductors in the input stage and 300Bs tubes in the output without aNegative Feedback Loop

The sound is stunningly transparent with full of delicacy and freshness.
Aurorasound, a hand-crafting studio in Yokohama, launched a new Monaural Power Amplifier PADA300B with use of 300Bs tubes in Push-Pull configuration.
A direct heating triode 300B has enduring popularity amongst vacuum tube enthusiasts. The new power
amplifier has a unique circuit structure designed by Mr. Shinobu Karaki, the owner of the Aurorasoundbrand. Mr. Karaki has a career of having worked for the US-based semiconductor manufacturer for 29
years. His amplifier circuit design is unique with fresh ideas, yet right on the target.
Mr. Karaki focuses on the advantages of vacuum tube as power amplifier device, yet, his circuit design
placed the transistors in the front-end (voltage amplifier), and the tubes in the output stage. In the past,
Aurorasound introduced front-stage amplifiers such as a Phono Equalizer Amp, and a Preamp usingtransistors. However, the previous power amplifier already in the market, PADA-EL34, uses discrete
transistor circuit in the input stage, and vacuum tubes in the output. The pre and the final stages arecoupled with FINEMET Core driver-transformer. With use of transistors in the preamp frontend stage,
low distortion, high S/N, and wider frequency range is achieved.
The push-pull configuration with two 300Bs delivers 28W of power output. It should be noted that theshown power output is rated at 2% distortion, and this distortion rate is low for vacuum tube
specification. In actual usage, this model is expected to deliver higher power output. The 300B hasexcellent linearity, thus PADA-300B has no negative feedback loop in the output stage. The filament of
300B is heated with AC current, not DC, because Aurorasound respects the original design scheme ofusing AC when the 300B was initially developed. Even if a hum noise is generated due to AC use for thefilament, it can be cancelled due to the push-pull design structure. (It has a hum balancer, as well)
Mr. Karaki is meticulously into parts selections as well. The front stage uses semiconductors, J-FET andBipolar Transistors, specifically developed for audio applications by NEC and Toshiba. These parts are nolonger in production; however, Aurorasound maintains ample inventories to meet any demands. In
addition, the output transformers and choke coils are of Lundahl in Sweden. These transformers are notencapsulated in plastic resin, in other words, they have open structure, which represents openlyexpansive feeling of sound, as well.
An evaluation listening was conducted at the Stereo Sound’s listening room using SACD/CD Player, andAccuphase system with B&W 800D3 speakers.
When the Track 8 on the CD “BARBARA/Bobino 1967” was played, where BARBARA sings only withcontrabass and accordion, the sound had such delicacy producing even faint vibrato and slight breathingvividly. The church music “Hodie” has ultra-high S/N, astonishingly transparent sound. You could almost
visualize the layers of the chorus ensemble floating in the air. It was also amazing that such low
frequencies from the pipe organ were accurately produced. “The Rite of Spring by Stravinsky”
conducted by Salonen on SACD disk is known to have an extremely wide dynamic range. So, in order totest how well the amp can perform, I increased the volume level without hesitation. I felt no concern
when the 800D3’s woofer pulsated with Gran Cassa, big bass drums, explosion.
This model PADA-300B is an ideal unit for those who want to be completely satisfied with the 300B’s
freshness and transparency, without even one spot of smear, yet having wide frequency range withexcellent transient response and SNR.
By Hiromi Wada