A Microphone preamplifier is an electronic circuit that serves the purpose of pre-amplifying weak audio signals. When the audio source (usually a microphone) sound level is too low. The main function of a Preamplifier circuit is to amplify small & weak signals from a microphone & other audio sources, before sending it for further amplification. All without compromising the intrinsic signal-to-noise ratio (SNR) of the input signal.
A Preamplifier amplifies the signal to a high voltage gain but does not have the current gain to drive the output. Hence, The improved signal from a preamplifier is usually sent to a power amplifier where the current is amplified. In this project, we will design a preamplifier circuit for a condenser microphone using a single 2N3904 transistor.
Hardware Components
The following components are required to make the Microphone Preamplifier Circuit
| S.No | Component | Value | Qty |
|---|---|---|---|
| 1. | Breadboard | – | 1 |
| 2. | Connecting Wires | – | 1 |
| 3. | Battery | 3-9v | 1 |
| 4. | NPN Transistor | 2N3904 | 1 |
| 5. | Potentiometer | 10k | 1 |
| 6. | Resistors | 10k, 100k | 2, 1 |
| 7. | Ceramic Capacitor | 0.1uF | 2 |
| 8. | Condenser MIC | – | 1 |
| 9. | Speaker | 8 ohm | 1 |
2N3904 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of 2N3904
Microphone Preamplifier Circuit
Working Explanation
The 10KΩ resistor on the microphones +ve terminal provides the specific voltage level required for this procedure. The 0.1μF capacitor (C1) stops the DC component of the transmission, allowing the AC input from the microphone to enter the transistor (Q1) through its base. The 10KΩ resistor attached to the transistor through its collector allows the triggering of the AC component, while the 100KΩ resistor acts as a collector coupling resistor.
Then the output audio signal is received from the collector terminal of the transistor & sent to an audio transducer (Loudspeaker) through the C2 capacitor (0.1μF), The gain of which can be tuned by connecting a 10KΩ pot. This circuit can easily be operated between 3V-9V DC.
Applications
- Used for electronic media production & recording applications such as live music & recording studio applications.
- A must for sound cards in various electronic devices such as computers & laptops.
- An important part of any telephonic device such as cell phones & smartphones.
