D.W. Fearn VT-1, Operating Instructions Manual, Page: 33 / 40

D.W. FEARN
VT-1 & VT-2 Microphone Preamplifers
33
Third Stage
The arm of the Attenuation potentiometer feeds the grid of the third stage (a 6072A), which
also operates Class A with a gain of approximately 30. This stage is capacitively-coupled to
the grid of the output stage through a polystyrene capacitor.
Output Stage
The output stage operates as a cathode follower, presenting a comparitively low output
impedance (approximately 800 ohms). The cathode output is coupled through a proprietary
polypropylene capacitor to the primary of the output transformer. This is a custom Jensen
transformer and is capable of low distortion output at levels exc24dBm.
VU Meter and Meter Amplifier
A two-stage IC operational amplifier is used to isolate the VU meter from the VT-2 output. An
output sample is derived from th secondary of the output transformer. The VU meter ampli-
fier and -12 volt regulator are constructed on a printed circuit board mounted above the main
chassis.
The meter and meter amplifier may be totally disconnected from the circuit by the Meter
switch. The meter calibrationis set with a 20-turn trimmer potentiometer. Reference level (0
VU) can be set from -20 to over +20dBm. The level indictor is a custom true VU meter con-
forming to ASA Standard C16.5-1954.
Power Supplies
Primary power from the AC mains is connected to the VT-1/VT-2 through a standard IEC
power input connector. The Power switch energizes all four power supplies. A fuse, accessi-
ble on the rear panel, protects the VT-1/VT-2. The Pilot lamp is a type 1819 bulb, operated
far below its rated voltage of 28. The life of the bulb is lengthened, and the light output is
more compatible with other modern studio equipment. The power transformer is a toroidal
unit custom-made for the VT-1/VT-2 and has primary taps for 100, 120, or 220-240 volt oper-
ation. The VT-2 may be rewired for different mains voltages.