D.W. Fearn VT-12, Руководство по эксплуатации, Страница: 29 / 37

D.W. FEARN
VT-12 Microphone Preamplifer
32
Input transformer
The input transformer is custom-made for D.W. Fearn by Jensen Transformers, Inc. and rep-
resents the state of the art in transformer design. It exhibits extremely flat fre quency
response, low phase shift, excellent square wave response, low distortion, and high noise
immunity. The secondary of is connected directly to the grid of the first amplifier stage.
Figure 4. VT-12 Block Diagram (one channel shown)
First stage
The first stage is a selected 12AT7 configured as a Class A voltage amplifier with a gain of
approximately 50. Negative feedback from the plate of the second stage reduces distortion,
flattens the frequency response, and makes the gain of the first two stages less dependent on
individual vacuum tube characteristics.
Second stage
The output of the first stage is coupled to the grid of the second stage through a polystyrene
capacitor. This stage operates as a Class A voltage amplifier with a gain of approximately 40.
The plate is coupled through a polypropy lene capacitor to the top of a rotary potentiometer
(Gain).