Yamamoto Sound Craft A-09S 300B Single Stereo Amplifier

300B reference machine. Dynamic, natural sound with non-feedback circuit and newly designed cut core transformer

The A−09S uses the 300B, the reference tube for modern vacuum tube amplifiers.output tubeThis is a non-feedback type single amplifier adopted for. The basic circuit uses a CR-coupled self-bias method using a pentode in the voltage amplification section, and uses a non-feedback method that does not use negative feedback (NFB) to make the most of the good basic characteristics, realizing a natural sound field and excellent dynamism.

High-FidelityCircuits and parts designed to

1. Updated transformer and power supply circuit

• Cut core type transformer: In place of the toroidal core type transformer, which lacked stability, newly designed cut core type transformers are used for the power supply, output, and choke coil transformers. It is more stable than the toroidal core type and provides a more dynamic sound.
• Schottky DC ignition circuit: In order to maximize the capabilities of the 300B, the rectifier is equipped with a double-wave rectified DC ignition circuit that uses a high-performance Schottky diode manufactured by IR in the United States that can handle large currents. By combining it with a smoothing capacitor with a small capacity, we aim to improve the freshness of the sound by simplifying the circuit and providing a faster sound.

2. Vacuum tube and driver stage

• High performance first stage tube C3m: High-performance German-made C3m tube is used for the first stage tube. It has excellent electrical characteristics and is characterized by very beautiful sound quality. By removing the metal case of the Roctal tube and using the glass tube as is, an even more natural sound has been obtained.
• 300B unadjusted drive: Most 300Bs from each company are designed to be replaced without any adjustment. There is no need to adjust hum balance, etc., and you can get the best sound without making any adjustments.

3. Carefully selected parts

• Resistance/Capacitor: The resistors are made by **DALE, which has a good sound. The main part of the capacitor is made of polypropylene film capacitor** with low distortion. These are filled and glued to ebony or bakelite cases with epoxy resin to improve strength and sound quality.
• Socket: All in-house Teflon sockets are used for high performance and high reliability. The slit structure provides a firm hold on the feet of the vacuum tube and prevents the effects of external vibrations.
• Terminals: The input terminal uses an original pin jack made of chrome copper, and the output terminal uses a large terminal with pure copper machined gold plating. It also supports extra-thick (8mm) speaker cables.

Design and housing structure

• Wood Chassis: The chassis is laminated with thin veneer of cherry wood and impregnated with phenolic resin to harden a wood-based material (Comprete). It is strong and electrically superior.
• Beautiful Finish: The transformer cover features cherry blossom side panels and a 2mm thick champagne gold aluminum alloy with durable anodized aluminum plating, creating a novel and beautiful design.
• African Ebony Leg: The legs are made of African ebony round rods with beautiful sounds and very hard. It is directly fixed to the chassis to accurately support the overall weight and enhance the vibration damping effect.

A-09S is the royal road of 300B single amplifiers,Yamamoto Sound CraftIt has been introduced as a model embodied in the precise design and material selection that is typical of it.
In the listening notes of MJ magazine and audio media outlets, it is first pointed out that while it has the luster typical of the 300B, the outline of the sound is not too sweet.

Midrange density and natural timbre

The biggest attraction is the texture of the midrange. The vocals and strings are thick yet transparent, and the natural tone without exaggeration is impressive. The temperature unique to the 300B is clearly felt, but it is not overly sweet, and the sound image is clearly visible.
In particular, in the reproduction of the voice, the distance and breathing at the corners of the mouth are naturally transmitted, and it is emphasized that it is not a "made luster".

Low-frequency braking and overall balance

As a single amplifier, it has good low-frequency braking, allowing you to hear bass with a core without relying on volume.
It's not the type to force large speakers to sound, but when combined with efficient speakers, the rhythm starts up clearly and the flow of the music doesn't stagnate.
The balance from low to high frequencies is good, and only part of the band is not noticeable.

Sound field expression and less listening fatigue

The sound field is excellent for expressing depth directions, and the context of the instrument is naturally depicted.
Although it is not the type that spreads out flashily, the sound image stands up quickly in the quiet background, so it is less likely to get tired even after a long audition.

Design and sound impact

Thorough consideration has been given to materials and structure, including the power transformer and output transformer, which is said to be directly related to the stability and transparency of the sound.
Rather than bringing the so-called "300B amplifier-likeness" to the forefront, it is positioned as a design that summarizes music in a way that allows you to listen to it naturally.

Overall Rating

The A-09S is a very well-balanced amplifier that retains the beauty expected of a 300B single amplifier while eliminating excessive coloring and sweetness.
The structure of the music does not collapse not only in jazz and vocals, but also in chamber music and small classical music, and it is introduced as a highly convincing one for listeners with a preconceived notion that "300B = atmosphere-oriented".