Listening to clean audio can be tough, especially in noisy environments. Unwanted background noise completely makes the signal unintelligible. The audio noise limiter circuit presented here overcomes this problem by limiting the noise peaks. It can be used with AM short-wave (SW) receivers and amateur radio (HAM) transceivers.
PARTS LIST :
IC1 – TL072 op-amp
D1, D2 – 1N4148 signal diode
Resistors (all 1/4-watt, ±5% carbon):
R1, R2, R4, R5 – 10k ohm
R3 – 470k ohm
R6 – 220 ohm
R7 – 4.7k ohm
VR1 – 10k ohm potentiometer
C1, C8 – 10uF, 35V electrolytic
C2 – 150pF ceramic disk
C3 – 100nF ceramic disk
C4, C6 – 2.2nF ceramic disk
C7 – 220uF, 35V electrolytic
CON1 – 2-pin terminal connector
JACK1, JACK2 – 3.5mm Audio Jack Socket
S1 – On/Off Switch
12V regulated power
Let us begin:
1.Connect a Red Wire to the pin of CON1 which will be connected to +ve terminal of 12V power supply. Connect the wire to S1’s terminal and connect another piece to Red Wire to S1’s other terminal. Connect a Black Wire to the pin of CON1 which will be connected to -ve terminal of 12V power supply.
2.(i) Connect IC1’s pin 4 to the Black Wire. Connect R6, R10 and C7’s +ve terminal in parallel to pin 8 of IC1. Connect R6’s other terminal to the Red Wire. Connect C7’s -ve terminal to the Black Wire.
2.(ii) Connect R1’s other terminal, R2 and C1’s +ve terminal in parallel to pin 3. Connect R2’s other terminal and C1’s -ve terminal to the Black Wire.
2.(iii) Connect D2’s -ve terminal, D1’s +ve terminal, C2, R3 and R7 in parallel to pin 2. Connect R7’s other terminal to C3 and C3’s other terminal to one of JACK1’s terminals. Connect JACK2’s other terminal to the Black Wire. Connect D2’s +ve terminal, D1’s -ve terminal, R4 and C2’s and R3’s remaining terminals in parallel to pin 1.
2(iv) Connect R5, C4 and C5 in parallel to R4’s other terminal. Connect pin 5 and C6 in parallel to R5’s other terminal. Connect C6’s other terminal to the Black Wire.
2(v) Connect C4 and C5’s other terminal to pin 6, pin 7 and C8’s +ve terminal. C8’s -ve terminal is connected to VR1. VR1’s output is connected to one of JACK2’s terminals. JACK2’s other terminal is connected to the Black Wire.
The circuit is not designed for use with mobile phones. It should only be used in SW and HAM receivers, and that too only for voice. The circuit is a low-pass filter to remove background noise.
Connect JACK1 to audio output of a SW receiver and JACK2 to any audio amplifier circuit.
For the original circuit, go here.