Yamamoto Acoustic Craft A-014 300B single stereo amplifier with input volume

The A-014 is a single stereo power amplifier with input volume that uses the famous 300B output tube. The basic circuit uses a CR-coupled self-bias system with pentode tubes in the voltage amplification section. The amplification section does not use negative feedback, but uses a non-feedback method to take advantage of the good basic characteristics and obtain a natural sound field.
The power transformer, output transformer, and choke coil of this amplifier all employ a high-bee cut-core transformer and an R-core transformer with extremely excellent regulation, and the output transformer uses a Teflon-insulated output transformer with a 0.1 mm thick high-bee cut-core. The output transformer uses a Teflon-insulated output transformer with a 0.1 mm thick high-bee cut core. Furthermore, the output transformer has a 16-ohm terminal in addition to the 8-ohm terminal, just right for 16-ohm speakers such as the vintage ALTEC 604E. The output transformer, which greatly affects sound quality, has a configuration comparable to that of the A-09S, a high-end model. In addition, the power transformer has separate transformers for the high-voltage circuit and the 300B heater windings to prevent interference between them.
The output tube section of the A-014 uses a DC ignition circuit with a low-impedance Schottky diode. Almost all 300B type vacuum tubes can be used interchangeably, and a double-wave rectification system is employed in the part that supplies heater voltage to the 300B vacuum tubes, which is advantageous for 300B sound quality due to its excellent regulation. For the rectifier, a high-performance Schottky diode manufactured by IXIS of the U.S. is used, which can handle high currents, and a small capacitor is selected for the smoothing capacitor, resulting in a sound with a superior sense of speed. The hum balancer and other components normally used are omitted to simplify the circuit and improve the freshness of the sound.

The driver stage of the A-014 amplifier uses a high-performance, highly reliable Siemens C3m pentode vacuum tube, which was developed in Germany at a relatively late stage in its design for telephone lines. It was developed in 1962, which is the latest period for vacuum tubes, and therefore has various excellent electrical characteristics and a very beautiful sound quality. This vacuum tube is enclosed in a metal case as a Rokutaru tube, but we have removed the case and use the glass tube. This gives a more natural sound quality. These tubes have a design life of more than 10,000 hours. The beautiful appearance of the mesh plate and the long service life make the replacement period of the vacuum tube extremely long, which is another great advantage and attraction. The A-014 uses this vacuum tube with screen-grid voltage stabilization to obtain excellent stability and a low distortion rate.
The driver stage of the A-014 amplifier is separated from the output circuit, rectified with a high-performance silicon first soft recovery tarp diode, employs a constant voltage circuit utilizing MOS FETs, and has a dedicated power circuit. The separate circuit system eliminates the driver stage from being affected by the output circuit, resulting in a clearer sound.
The chassis of this unit is a gold 2mm-thick steel chassis with high rigidity. The front panel and transformer cover are made of molded plywood made from cherry wood, which is formed in an arched shape, and this combination gives the unit a unique and attractive appearance. The high-strength yet soft appearance will allow you to fully enjoy the pleasure of using the product.

A new type of meter is used for this unit, which can display both the current of the 300B output stage and the plate voltage of the driver stage. It is now possible to check the operation status of the output stage as well as the driver stage. The life of the vacuum tubes can also be checked immediately. In the event of an amplifier malfunction, it is possible to quickly determine which part is the cause.
Most of the resistors used in the A-014 are made by DALE of the United States. Their sound quality is so superior that it cannot be compared with that of domestic products of the same class. The reliability of the components is also much higher because they are made in accordance with the U.S. MIL standards.
Polypropylene capacitors are used in key locations. Since these capacitors have a significant effect on the sound quality not only in the signal circuit but also in the power circuit, polypropylene capacitors are used in key locations including the power circuit to improve the sound quality. For internal wiring, instead of using printed circuit boards, 3mm thick Bakelite boards are used for fixing and wiring components. This increases the mounting strength of the components and improves reliability. The Bakelite board is directly fixed to the steel chassis, and components and vacuum tubes are firmly fixed. The increased strength of the components reduces the effects of vibration and improves sound quality.

The input terminals of this unit use the company's original top-quality pin jacks with machined chrome copper terminals for the external conductors, machined bronze round pin terminals for the internal pins, and Teflon as the insulating material. The output terminals are machined brass, gold-plated, and Teflon-insulated high-quality terminals. Speaker cables up to 4 mm in thickness can be connected to it.

Type	300B Single Stereo Power Amplifier with Input Volume
Tubes used	300B x2 (300B tube sold separately for standard specification), C3m x2, 5U4G x1 included except output tube
Maximum output power	8W+8W
Frequency Response	15Hz~22kHz(-3dB)
Residual Noise	0.8mV
Input impedance	100kΩ
Size	500(W)294(D)208(H)mm
Weight	16.2kg

The A-014 is available in three types of output tubes: one sold separately, one with a JJ 300B, and one with a 300BXLS vacuum tube manufactured by Emission Lab of Germany. The A-014 is designed to be used with most 300B tubes from various manufacturers, and no adjustment is required. There is no need to adjust the hum balance or anything else. The best sound can be obtained without any adjustment. The tone has a good S/N ratio and is not muddy at all, but the contours are clear and the backbone is very strong. There is no oozing or ambiguity, and it is a rare thing to achieve such a clear sound without relying on vacuum tubes. The piano, while full of transparency from bottom to top, has no hard edges and is rich in freshness and reverberation, with no muddiness and a clear focus. The vocals were expressive and full of live sound, never too much, and very expressive. The jazz is more bouncy than one would expect from a 300B single, with a dynamism that one would not expect from a 300B single. The wood bass is not blotchy, and the pitch is deep and subdued. The saxophone was tenacious and had a rich and lustrous impression. The orchestra is vivid and instantaneous, with strong contrasts of intensity and weakness. The purity of the sound is so high that every note of every instrument is lively and rich in freshness. A rare finish with clarity, strength, and added freshness.