As being electronics hobbyist we all know about timer IC 555. Timer IC 555 is one of the most popular IC of all time because of its application. This IC have various application like clock pulse generator, time delay circuit etc. Here, is one another application of 555 timer IC i.e. Audio Amplifier using 555. We are going to use 555 timer IC rather than conventional amplifier IC because it has unique features like low audio distortion, high efficiency with high base.
PWM is the method which by 555 timer IC in order to process audio signal.
Circuit Description and Working Audio Amplifier Circuit using 555 IC
As its name suggest Audio Amplifier Circuit using 555 IC shown in figure 1 is built around 555 IC with some other component like audio transformer, resistor, capacitor etc. Timer IC 555 is wired in astable mode in order to produce PWM signal where variable resistor VR1 is used to adjust the audio distortion.
Audio input from various source like (computer, mobile, etc.) is given to one terminal of audio transformer which is used here as mediator between audio source and amplifier circuit. Audio transformer is used to match input-impedance and the transformer used here is suitable for output of computer or mobile to input of circuit shown in figure 1.
Amplitude of input audio signal is responsible for varying the carrier frequency pulse width. Capacitor C2 connected between input and output of audio circuit (Feedback) is used to check reproduction of suitable audio signal. Normally L-C network is utilized in order to reject the unnecessary carrier frequency but in this circuit, we are not using because speaker didn’t respond to high frequency thus there is no need of L-C circuit.
The output is connected to 1W, 8-ohm loudspeaker for suitable audio output. While testing in BEP lab we had used audio source from ACER laptop, where input audio transformer is supertronix KEC.
PARTS LIST OF AUDIO AMPLIFIER CIRCUIT USING 555 TIMER IC
|Resistor (all ¼-watt, ± 5% Carbon)|
|R1 = 680 Ω
R2 = 10 KΩ
VR1 = 100 KΩ
|C1 = 680 pF
C2 = 22 nF
C3, C5 = 100 µF/35V
C4 = 470 µF/40V
|IC1 = NE555|
|X1 = Audio Transformer
LS1 = 8-ohm, 1W speaker