Experiment 10

Preamplifier (preamp)

Amplifier specifically designed for weak, high-impedance signals is a _

Weak signal → Preamp → Power Amp → Speaker

Signal chain in audio system is _

Signal-to-noise ratio (SNR)

Preamplifying early improves the _

High Zin, Low Zout

Ideal preamplifier impedance properties are _

High input impedance

Preamp needs _ to avoid loading down source

Low output impedance

Preamp needs _ to deliver signal to next stage

Linearity

Preamplifier property: constant gain across entire operating range is _

Harmonic distortion

Non-linearity in a preamp causes _

Voltage gain

Preamplifier focuses primarily on _

Current gain

Power amplifier focuses primarily on _

Millivolt-level signals

Preamplifier deals with _ signal levels

Low-impedance loads (4–8 Ω speakers)

Power amplifier drives _

High-impedance to low-impedance converter

Preamplifier role in impedance is _

Audio, sensors, buffer circuits

Three preamplifier application areas are _

Common Emitter (CE)

BJT configuration used in Experiment 10 preamplifier is _

Q2N2222

NPN BJT transistor used in Experiment 10 preamp is _

NPN

Q2N2222 transistor type is _

12 V

DC supply voltage in Experiment 10 preamplifier circuit is _

500 kΩ

R1 (bias resistor) value in preamp circuit is _

10 kΩ

R2 (collector resistor) value in preamp circuit is _

1 kΩ

R3 (emitter resistor) value in preamp circuit is _

500 µF

C1 and C2 (coupling capacitors) value in preamp circuit is _

100 µF

C3 (bypass capacitor) value in preamp circuit is _

Sets base bias current / Q-point

R1 (500 kΩ) function in preamp circuit is _

Converts IC to output voltage / sets voltage gain

R2 (10 kΩ) function in preamp circuit is _

DC Q-point stability (emitter degeneration)

R3 (1 kΩ) function in preamp circuit is _

Blocks DC, passes AC signal

Coupling capacitors (C1, C2) function is _

Shorts R3 at AC, restores full AC gain

Bypass capacitor (C3) function is _

AC negative feedback (emitter degeneration)

Without C3, R3 introduces _ reducing gain

XC = 1/(2πfC)

Capacitor impedance formula is _

Very low at AC, infinite at DC

Capacitor impedance behavior: _

Negative feedback removed

C3 shorts R3 at AC so _

DC stability preserved

C3 allows AC bypass while R3 still provides _

Input coupling capacitor

C1 role in preamp: _

Output coupling capacitor

C2 role in preamp: _

Emitter bypass capacitor

C3 role in preamp: _

Voltage gain and power gain

CE chosen for preamp because it provides _

180°

CE preamplifier introduces _ phase inversion