SOULNOTE Kato’s “This Is What I Want to Say” Series 1207. [About the A-0 ver.2, Part 2]: Single Push-Pull Output Stage with TO-220 Transistors – “Specifications and Sound Have Almost No Correlation.”
I always say this, but perhaps the only spec that correlates reasonably well with sound is frequency response. However, I’m referring to the bare frequency response before feedback. This is because it directly affects dynamic characteristics (transient response). Of course, that’s not all.
All SOULNOTE products use no-feedback circuits, so naturally, all have bare frequency responses. Even among them, the A-0 ver.2’s frequency response is unmatched: 350 kHz at -1 dB (400 kHz for headphone output and preamp output). This is possible thanks to the use of small, single-push-pull TO-220 packaged transistors in the output stage, which have low Cob (collector output capacitance, which largely determines the bare high-frequency response) and excellent high-frequency characteristics. However, maximum output power is sacrificed, capping out at 10W.
That’s what I mean when I say, “A high-end amplifier that’s fully focused on quality, only possible by limiting output to 10W.”
The sc1.0, the predecessor to the original A-0, began development as an ultra-powerful preamp and headphone amplifier. This was over 15 years ago. During development, I tried playing a speaker with it, and surprisingly, it worked! And it sounded amazing! So, midway through development, speaker terminals were added and the amplifier was converted into an integrated amplifier. At the time, I never imagined that a mere 10W amplifier would become such a popular product.