The Yamaha A-400 is a stereo amplifier that was manufactured by Yamaha Corporation. It is part of the A-series amplifiers produced during the 1980s. The A-400 was designed to deliver high-quality audio performance and featured a solid-state design with a power output of around 40 watts per channel. It included various input and output options such as phono, tuner, CD, and tape inputs as well as speaker outputs for two pairs of speakers. The amplifier also had tone control and balance adjustment options. The Yamaha A-400 was known for its reliable performance and was popular among audiophiles and music enthusiasts during its time.