I was checking out some transistor amplifier circuits online when I came across this one. enter image description here

Now my question is what is the use of 10 kilo-ohm resistor that is connected between the power and the input terminals? What happens is this particular resistor is removed? Please explain.


It applies a bias current across the microphone. As the microphone is of the type that changes resistance in response to sound. Thus forming a voltage divider that is connected to the base of the transistor via the decoupling capacitor.


What happens is this particular resistor is removed? Please explain.

If your input does not require phantom power (most electret microphones will) then you do not need to the 10k resistor.


This Resistor controls the collector current passing in the transistor and affects the bais point . So according to the specific amplification (GAIN) the designer wanted has choosen this resistor to be 10k using the basic transistor equations.

enter image description here enter image description here

for more details : The NPN Transistor

  • 4
    \$\begingroup\$ I think you missed the point of the question. He's not asking about the resistor to the collector. He's asking about the resistor farther to the left that provides power to an electret microphone. \$\endgroup\$
    – JRE
    Jan 26 '16 at 10:17
  • \$\begingroup\$ Great answer to another question. It's happened to most of us! \$\endgroup\$
    – Transistor
    Jan 26 '16 at 14:07
  • \$\begingroup\$ sorry i goofed up \$\endgroup\$
    – ElectronS
    Jan 26 '16 at 17:16

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