Amplifiers and Their Working

Sub: Sci

Sec: Msc

Introduction

Amplifiers have transformed various fields, including entertainment, astronomy, search and rescue, and medical diagnostics.
They boost electric signals for various applications.
Power amplifiers exist in multiple classes, each suited for specific uses.

Microphone – A Transducer

Converts sound energy into electrical signals.
Different types exist for various applications.
Condenser Microphones:
- Use capacitors to transduce audio signals.
- Consist of two plates with a dielectric medium.
- One plate is replaced with a vibrating diaphragm.
- Changes in capacitance convert sound to electrical signals.

Sound Amplification Process

Preamplifier (Preamp)
- Acquires input voltage signal and supplies more energy while minimizing noise.
- Amplification is performed by active components like transistors.
Voltage Amplification using a Transistor
- Bipolar Junction NPN Transistor:
  - Has three terminals: base, collector, and emitter.
  - Small input voltage applied between base and emitter (forward-biased).
  - Electrons flow from emitter to collector, creating large current.
  - External high voltage at collector increases the voltage swing.
  - The amplified signal retains the shape of the original but has a higher voltage.
Driver and Power Stages
- Driver Stage: Keeps voltage constant while increasing current.
- Power Stage: Increases both voltage and current before sending it to the loudspeaker.

Types of Power Amplifiers

Loudspeaker – Producing Loud Sound

Components:
- Voice Coil: Wire coil placed in an external magnet.
- External Magnet: Creates a strong magnetic field.
- Diaphragm: Vibrates to produce sound.
Process:
- Input voltage applied to the voice coil generates a large current.
- Interaction of coil’s magnetic field with external magnet causes motion.
- Coil motion vibrates the diaphragm, producing sound.
Enhancement:
- The external magnetic field is made stronger
- Larger diaphragm and the input signal more powerful.
- Loudspeakers can also be built with smaller diaphragms with faster-moving membranes to facilitate high frequency sounds and larger diaphragms to facilitate low frequency ones.