Condenser Mike Pre-Amplifier Circuit

Condenser Mike COND MIC Pre-Amplifier

Condenser Mike Pre-Amplifier Circuit

need often arises for a sensitive sound pick-up device, whether it is to be used as a simple microphone or a more exotic device as a sound operated alarm, a bugging device or a sound operated flash (for stop action photography) the list is quite unending.

The circuit given employs a condenser microphone as the transducer. Since output of the condenser microphone  is quite low, it usually has an FET amplifier built into the case.

Condenser Mike Pre-Amplifier Circuit mic microphone diagram

R1 1.2k
R2 2.7k
R3 33k
R4 6.8k
R5 3.3k
R6 100
R7 560k
R8 4.7k
R9 1k
VR1 10k
C1 47µF 10V
C2 0.1µF
C3 0.1µF
C4 220µF 10V
C5 10µF 10V
Q1 BC149C
Q2 BC147B
MIC Condenser Mike

This amp is powered by the R1, R2 resistor network.

The output of condenser microphone is fed to a two stage amplifier. Transistor T1 (BC149C) utilising current series feedback forms the first stage. The second stage comprising transistor T2 (BC147B) is connected in the voltage shunt feedback configuration. These two stage provide sufficient gain to pick up even the slightest whisper.

The circuit requires a 4.2 volt supply.This may be obtained, as in the prototype, with a 1kΩ (R9) resistor as shown in the diagram. The value of this  resistor may be altered. to suit a supply voltage other than 6 volts.

Condenser Mike COND MIC microphone pin configuration

Condenser Mike Pin Configuration

Output of the microphone amplifier can be made variable by connecting a 10kΩ potentiometer / Preset as shown.

Circuit’s gain can be increased by reducing the value of R6 to 47Ω or 22Ω, depending on the input sensitivity of the main amplifier system. Increase in gain was also observed by using 3V supply and eliminating R9 altogether. The microphone should be housed in a small round enclosure.

Please send your ideas, which are very important for our success…

17 comments on “Condenser Mike Pre-Amplifier Circuit
  1. Taylor Dyke says:

    This circuit works great!, how can i reduce some of the background noise leaking through the circuit?

  2. seetharaman says:

    Hi Taylor shift the volume control between mic and Q1. It will solve your problem

  3. Wilson Gates says:

    Really awesome article! Honest..

  4. Steve says:

    This circuit works great!, how can i reduce some of the background noise leaking through the circuit?

  5. Dirk Davis says:

    Incredibly great read. Truely.

  6. Emily says:

    Hi Taylor shift the volume control between mic and Q1. It will solve your problem

  7. Bookmarking now thanks, found you through Bing.

  8. You seem very knowledgeable in your field.

  9. Rajeesh BK says:

    It is very usefull

  10. Garren Handson says:

    Hi this really helped me a lot, however would it be possible to incorporate a on/off power switch for the battery or voltage source?

    Also how would I hook this preamp circuit to an amplifier circuit?

  11. Garren Handson says:

    Also would it be possible for you to send me some pics of the finished circuit?

  12. kiran says:

    hi sir,
    can i know what is this circuit exactly?i think that when i speak from mic the sound will be heard by the output[speaker]am i right please tell me because i am a beginner.

  13. Rumira Daksith (age13 ) says:

    this circuit is grate

  14. Posporo says:

    Hello newbie here… I would like to ask if theres any substitute for the transistors because they are not available here. Thanks 🙂

  15. Electronic Engineer says:

    The microphone pin-out is wrong.
    You have used the “b” bin in your schematic connected to ground.
    It should be “a”.
    As you can also see in the photo of the microphone, the earth is connected to the case.
    I have used this same condenser mic and connected it the right way, and it works well.
    Here is another website to confirm the correct pin-out:

  16. kaish says:

    how to get its output???
    it hasn’t shown any output value …

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