Also known as “American Preamps Imitated”–these projects are inspired to various degrees by the classic 1970’s preamps designed and manufactured by Automated Processes Inc., or API. The “API Sound” is commonly thought to be a result of the unique strengths and limitations of API’s proprietary discrete operational amplifier, the 2520, and input and output transformers. In particular, it is the relatively slow slew-rate (transient response), small bandwidth, and high amount of harmonic distortion that give API mic preamps their euphonically “up front,” “warm,” and at times “agressive” sound.