The Avalon VT737 SP Tube Voice Channel. Delivers impeccable clarity with tube warmth and presence for your mic, instrument or line mono channel. The Avalon VT737 SP Mono Mic Pre/Compressor/EQ is a combination tube preamp, opto-compressor and sweep equalizer, with output level and VU metering in 2 rackspaces. Balanced mic, front-panel instrument DI, and balanced line inputs. Class A preamp uses 2 cascaded, dual vacuum-tube triodes configured with minimum negative feedback. The Avalon Vt 737sp has a high-gain switch, high-pass filter, and hardwire relay bypass..