As being electronics hobbyists 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 has various applications like clock pulse generator, time delay circuit, etc.
Here, is another application of 555 timer IC i.e. Audio Amplifier using 555. We are going to use a 555 timer IC rather than a conventional amplifier IC because it has unique features like low audio distortion and high efficiency with a high base.
PWM is the method by 555 timer IC to process audio signals.
Circuit Description and Working Audio Amplifier Circuit using 555 IC
As its name suggests Audio Amplifier Circuit using 555 IC shown in figure 1 is built around 555 IC with some other components like an audio transformer, resistor, capacitor, etc. Timer IC 555 is wired in an astable mode to produce a PWM signal where variable resistor VR1 is used to adjust the audio distortion.
Audio input from various sources (computers, mobile, etc.) is given to one terminal of the audio transformer which is used here as a mediator between the audio source and amplifier circuit. The audio transformer is used to match input-impedance and the transformer used here is suitable for the output of computer or mobile to the input of circuit shown in figure 1.
The amplitude of the input audio signal is responsible for varying the carrier frequency pulse width. Capacitor C2 connected between input and output of the audio circuit (Feedback) is used to check the reproduction of the suitable audio signals. Normally L-C network is utilized to reject the unnecessary carrier frequency but in this circuit, we are not using it because the speaker didn’t respond to high frequency thus there is no need for an L-C circuit.
The output is connected to a 1W, 8-ohm loudspeaker for suitable audio output. While testing in the BEP lab we used an audio source from the ACER laptop, where the input audio transformer is supertonic 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 |
| Capacitors |
| C1 = 680 pF (Ceramic Disc)
C2 = 22 nF (Ceramic Disc) C3, C5 = 100 µF/35V (Electrolytic Capacitor) C4 = 470 µF/40V (Electrolytic Capacitor) |
| Semiconductors |
| IC1 = NE555 (Timer IC) |
| Miscellaneous |
| X1 = Audio Transformer
LS1 = 8-ohm, 1W speaker |