Output transformerless

Output transformerless (OTL) is a term which describes a subset of vacuum tube audio power amplifier topologies, all of which omit an output transformer for the purpose of greater linearity and fidelity. Conventional vacuum tube amplifier designs rely upon an output transformer to couple the amplifier's output stage to the loudspeaker. Instead, OTLs use one of two primary methods for output stage coupling: direct coupling (DC) or capacitive coupling (AC).