The Adcom is not a passive preamp as it has gain.See the following quote from the Stereophile test.
Other than glue logic and the transistors used to drive the relays, the 12 active devices—four gain blocks, each with three devices—are HEXFETs from International Rectifier. The output stage is intended to function as a pure voltage source, making the GFP-750 relatively immune to cable differences or low amplifier impedances. As we've come to expect from Adcom, the preamp sports a honkin' big toroidal transformer, with multiple secondary windings for each channel. A large heatsink on the left-hand side carries the power supply regulator chips.
Passive preamps have no active stages at all, just input selectors and volume controls. A very good passive is the Creek OBH 22. The Adcom has a passive phono equalization I believe but has, as you see, gain stages.
Other than glue logic and the transistors used to drive the relays, the 12 active devices—four gain blocks, each with three devices—are HEXFETs from International Rectifier. The output stage is intended to function as a pure voltage source, making the GFP-750 relatively immune to cable differences or low amplifier impedances. As we've come to expect from Adcom, the preamp sports a honkin' big toroidal transformer, with multiple secondary windings for each channel. A large heatsink on the left-hand side carries the power supply regulator chips.
Passive preamps have no active stages at all, just input selectors and volume controls. A very good passive is the Creek OBH 22. The Adcom has a passive phono equalization I believe but has, as you see, gain stages.