Thursday, January 20, 2011

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Audio Peak Level Indicator by Op-Amp LM324

This circuit was designed to provide a valuable test equipment tool for sound reinforcement systems like guitar amplifiers and the like. Used in conjunction with a signal generator it can be of considerable help in setting and controlling levels through any amplifying chain.
Audio Peak Level Indicator Circuit
The circuit is formed by an input buffer and ac to dc voltage converter (IC1A) feeding a window comparator (IC2A, IC2B, IC2C) which illuminates one of three LEDs at a time. No setup is required: if correct values are used for resistors R3 to R7, LED D1 will illuminate at 0dB input (0.775V RMS), LED D2 at +5dB input (1.378V RMS) and LED D3 at +10dB (2.451V RMS).

  • Maximum current drawing: 12mA when one of the three LEDs is illuminated and less than 4.5mA when the input level is below 0.775V.
  • LEDs of different colors can be used to mark any of the three different levels.
  • Input pins of unused op-amps must be tied to negative ground. Output pins must be left open (see the upper left corner of the drawing).
List Component of Audio Peak Level Indicator Circuit
R1       : 300K  1/4W Resistor
R2 : 1M2 1/4W Resistor
R3 : 510K 1/4W Resistor
R4 : 220K 1/4W Resistor
R5 : 91K 1/4W Resistor
R6 : 160K 1/4W Resistor
R7 : 56K 1/4W Resistor
R8,R9 : 100R 1/4W Resistors
R10 : 220R 1/4W Resistor
C1 : 100nF
C2 : 1µF/63V
C3 : 10µF/25V
D1,D2,D3 : LEDs (Any coloring at will)
IC1 : LM393
IC2 : LM324
IC3 : 78L05
SW1 : SPST Toggle or Slider Switch

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