Here is a simple circuit that can be used to check the sound levels.The sound pressure meter is vey useful in setting up home theater systems , if you need to test the sound pressure of each channels on different positions in the room.

The circuit is nothing but a non- inverting amplifier based on op-amp CA 3140 9 (IC1).The sound picked by the condenser mic will be amplified by the IC1 and rectified by the bridge D1 to drive the meter M1.The deflection on the meter will be proportional to the pressure of the sound falling on the mic.The switch S1 can be used as an ON/OFF switch.

Circuit diagram with Parts list.



  • The bridge D1 can be a 1A bridge.If 1A bridge is note available,make one using four 1N4007 diodes.
  • The circuit ca be powered by using a 9V PP3 battery.
  • The capacitors must be rated 10V.
  • Mount the IC1 on a holder.


  1. how can i know the calibration of the meter that i am connecting in the circuit? or how much dB of sound will show deflection of 1uA??

  2. cl dickinson

    This is “just about” the circuit I (and about 10.000 other bands) need. From across a room, the band needs to be able to tell if the sound level is rising (of course it is)
    So…. instead of a meter, I need to drive a LED array (say 10 bright LEDS) (Like the “sound level meter” also on this site).
    So.. how could I integrate these two concepts together?