Bipolar Junction Transistors

Transistor Attenuator

This circuit is an emitter follower with a variable gain input and an adjustable output DC level.

The input signal is developed across R₁ to ground. Since the emitter follower (Q₁) has high input impedance, the amount of signal fed to its base through the current limiting resistor R₂ will be proportional to the setting of the arm of R₁. As the arm of R₁ is moved closer to the input, the signal fed into the emitter follower is increased.

The emitter of Q₁ is connected through the level pot R₃ and the resistor R₄ to the -18V supply. As the level pot is adjusted, the DC that appears at output can be varied with a minimum effect on the signal amplitude.