In the world of audio amplifiers, the wide kinds of semiconductor amplifiers, tube amplifiers, etc. are released. Therefore, the respective audio features can be enjoyed as a hobby.　Especially tube power amplifiers adopting a tube called 'fine tube' such as 2A3 or 300B have well-established sound quality that cannot be expressed by semiconductor amplifiers and they are accepted consistently even in the modern era.　"We would like to taste the best sound produced by a 300B amplifier composed by a parallel single-ended circuit adopting 300B which is the best tube among them and a circuit strongly driven by a transformer-coupled circuit adopting 2A3." In 2016, we have developed the monaural power amplifier, MA-2000, to respond to the user's thoughts.