We service and test what we sell. This one has very low distortion and flat frequency response. Sonically fantastic. Rare and Classic Melos SHA-1 Stereo Tube Preamplifier / Headphone Amplifier Serviced (we have the schematic) New Tubes. 2 line level inputs. 2 headphone jacks. Probably one of the best headphone amplifiers ever made. Excellent as a preamplifier. Simple circuit uses one 6DJ8 per channel in a long tailed pair. High quality ALPs volume control. Very high quality parts including gold plated RCA jacks. Servo control for dc offset. Highly Regulated power supplies using three terminal regulators, both filament and high voltage. Toroidal power transformer. Headphone output can drive low impedance dynamic headphones to loud clear levels. See Stereophile review from early 90s. This is the only one to buy. The other models are problematic.