• PST 100 MKII: Combo Valve & Transformer Preamp
• PST 100 TA: Transformer Attenuator Preamp 

PST 100 MKII

Most manufacturers develop a circuit for their power amplifier and then use the design for their preamplifier. The job of a power amplifier is to amplify the signal and drive the loudspeakers. That of a line preamplifier is to draw together the various source components; to attenuate the signal in order to achieve "volume control"; to have low enough output impedance in order to drive the cables; and finally, to provide gain if it is required. It performs totally different duties to those of a power amplifier and needs to be designed in a totally different manner. 

Conventional wisdom suggests that the most critical part of a preamplifier is the active circuit design. Ypsilon, however, believe that the means of signal attenuation (the volume control) is the most critical to the overall sound of a preamplifier. Most designers use resistor attenuators for volume control. Ypsilon themselves have used resistor attenuators with high quality resistors (Vishay, Holco, tantalum types etc.) in the past, but that was before they developed a very special transformer as the means of attenuation. It was immediately apparent just how grainy and discontinuous resistors sound, even the best of them. The short explanation of this observation is that the series resistor transforms the constant voltage into current and the parallel resistor the constant current into voltage. The materials used in resistors are far from ideal as conductors... they sound much worse than pure copper or silver... and they do a lot of harm to the signal.