Audio Peak Level Indicator By Op-Amp

test equipment tool for sound reinforcement systems like sound amplifiers and the like. 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.

Skema Rangkaian Audio Peak Level Indicator By Op-Amp

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).

The circuit was optimized for low current consumption as it was intended for battery operation. To achieve this, the best arrangement has proven to be the one using two different op-amp types for IC1 and IC2. In fact the LM393 IC was not operating satisfactorily as dot-mode LED driver, whereas the LM324 was unable to charge C2 in the linear way, as expected. Therefore, the final circuit is some op-amp wasting, but the small added cost will be quickly compensated by battery savings.

List Component:
R1    : 300K         D1,D2,D3 : LEDs
R2    : 1M2          IC1      : LM393
R3    : 510K         IC2      : LM324
R4    : 220K         IC3      : 78L05
R5    : 91K          SW1      : SPST  Toggle or Slider Switch
R6    : 160K         B1: 9V  PP3 Battery
R7    : 56K
R8,R9 : 100R
R10   : 220R
C1    : 100nF
C2    : 1µF/63V
C3    : 10µF/25V