The Little Dot I+ is a hybrid transistor-vacuum tube headphone amplifier, which combines the smooth, musical sound of tubes with the high output current of transistors. The vacuum tube stage is run in Class-A, the MC33078 operational amplifier (socketed) provides voltage amplification, and BD139/BD140 transistors serve as output buffers. The Little Dot I+ is specifically designed and optimized for driving low impedance headphones that require high current to perform to their full potential. Depending on how the switches are configured, three different families of vacuum tubes can be used (EF95, EF92, and 408A). With two gain settings and DIP switches for vacuum tube rolling, the Little Dot I+ offers versatility in a tiny footprint!