I made a sound amplifier and it requires a Capacitor, i removed the capacitor and my amplifier stopped working, what was amplifier doing in that circuit? Why on removing it circuit stopped working.enter image description here

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    \$\begingroup\$ Because it was needed for the operation of the amplifier? Post a schematic, so we can identify said capacitor and advise its function. \$\endgroup\$
    – Neil_UK
    Mar 18, 2018 at 5:55
  • \$\begingroup\$ @Neil_UK uploaded the picture \$\endgroup\$ Mar 18, 2018 at 5:59
  • \$\begingroup\$ The transistor needs to operate as "linear amplifier", which requires the transistor be biased "on". To be "on", the transistor needs approximately 0.6 or 0.7 volts across base-emitter, set by regulatory (negative) feedback through the 2,200 ohm resistor. The capacitor separates this internal base bias from the external DC (could be zero) average of your signal source. \$\endgroup\$ Mar 18, 2018 at 14:23

2 Answers 2


Without the capacitor, a DC coupled input will pull the base down to ground, biassing the transistor off.

In this case, the capacitor is being used as a coupling capacitor, that transmits AC signals, while allowing a DC voltage to exist across it without a DC current flowing.


Capacitors are used here in order to pass the audio signals without its DC level is interfering with the transistor's bias.

For instance, one transistor has a collector voltage of 5V, and you are directly connecting the 1v base biased transistor with it will always turn on the second transistor which means the DC level of the first transistor will interfere with the audio signal that is passing to the second transistor.

If you use a capacitor in between these two transistor, it will only pass the audio signals to the second transistor and it prevents the DC interference.

Source: Capacitor in amplifier transistor


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