D.W. Fearn VT-1 Operating instructions manual - page 34

D.W. FEARN

VT-1 & VT-2 Microphone Preamplifers

34

Filament Supply

The power transformer output is rectified by a bridge rectifier and filtered before being reg-

ulated to 12.0 volts by a three-terminal regulator. The negative output of this supply is

grounded. Although the filaments are rated for 12.6 volts, utilization of 12.0 volts has no

effect on the operation of the VT-1/VT-2.

Meter Amplifier Supply

A negative version of the filament supply provides regulated -12 volts for the IC operational

amplifiers in the meter amplifier circuit. This regulator is located on the Meter Amp PCB.

B+ Supply

Two separate regulated voltages are required for the plates of the VT-1/VT-2. The B+ is fil-

tered with long-life, low-leakage, computer-grade filter capacitors before being regulated and

extensively bypassed and decoupled. The negative side of the supply is grounded. Two sepa-

rate B+ supplies are used in the VT-2, one for each channel.

+48 Supply

The regulator circuitry is on the power supply printed circuit board. The actual output of this

supply is 51 volts, which is reduced to 48 volts through the decoupling resistor at the micro-

phone input (see Phantom Power, above).