Spatial Audio Raven Preamp

The Raven will drive any power amp with an input impedance between 10K to 220K, in either RCA single-ended mode (which uses half the transformer secondary) or XLR balanced mode (which uses the full secondary). The output transformer is optimized to deliver clean square waves over this impedance range.

As Lynn said, don't sweat long XLR cables.  The Raven will happily drive them.

Transformer coupled line amplifiers were the recording, broadcast, and television-audio standard from the Thirties through the Seventies. After that, discrete-transistor op-amps (discrete output transistors have enough power to remain in Class A with 600-ohm loads) became the industry standard.

[A bit of history: when 16 and 24 channels became the industry norm, tube line amps became impractical due to heat and size concerns. The first integrated op-amp specifically designed for professional use was the Signetics 5532/5534 released in 1979, while the discrete-transistor Jensen JE-990 became an industry favorite after 1980.]

The Raven is simply a modernized and fully balanced version of a studio line amplifier from preceding decades, with modern power supplies, computer optimized transformers, Khozmo fully balanced switched-resistor volume controls, and point-to-point wiring.