The Avalon VT-737 SP features a combination of TUBE preamplifiers, opto-compressor, sweep equalizer, output level and VU metering in a 2U space. The VT-737 SP preamplifier has three input selections: 1. Transformer balanced microphone input, +48v phantom selection. 2. Instrument DI high source input with jack located on front panel. 3. Balanced line input, discrete highlevel Class A. The high-performance preamplifier utilizes two cascaded, dual vacuum tube triodes configured with minimum negative feedback. A high gain switch boosts the overall gain of the preamplifier. The four high quality tubes are configured as singled ended anode coupled followers. A passive-variable high pass filter and hard-wire relay bypass completes the input signal conditioning. The phase reverse relay is available on all three inputs.