The project sound level meter circuit shown here comprises a display circuit for 10-segment resolution i.e. used to indicate sound level up to 10 levels.
Recording of sound in the studio involves critical adjustment of recording levels and level of bias current. If the level of sound is very much it may cause some distortion while a low level of sound reduces the SNR (Signal to Noise Ratio) as a result the sound may be too noisy.
Care should be taken while recording sound to regulate the signal so that the sound level is exactly what is required for hi-fi reproduction.
Working and Description of Sound Level Meter Circuit:
The project Sound Level Meter Circuit is built around an amplifier IC TBA810 and display circuit as shown in figure 1. IC1 is used to provide the required amplification before the signal is fed to the display module. The signal is rectified by D1 and further filtered by capacitor C10Â. This rectified signal is given to the bases of transistor T1 to transistor T10 through resistors 10K. This resistor is used to saturate transistors.
The emitter of each transistor is given a larger threshold voltage than the preceding only by 0.6V so that they saturate, its LED glows in its collector circuit. Diodes D2 to D10 compensate for the loss of voltage for each transistor caused due to D11 to D19.
Although calibration of the project Sound Level Meter Circuit is tedious, once calibrated, the project Sound Level Meter Circuit need not be touched again. Connect the output of the pre-amplifier to the input of this circuit.
A well-calibrated Sound Level Meter Circuit is required to check the sound level from this circuit. If the sound signal indicates low or high-level signals, adjust preset VR1 and repeat the procedure until the correct level is obtained. Now seal the preset and do not tamper with it again. The project Sound Level Meter Circuit is easy to construct though it is a little costlier than the V-U meter indicator, but it is worth the cost.
PARTS LIST OF SOUND LEVEL METER CIRCUIT
| Resistor (all ¼-watt, ± 5% Carbon) |
| R1 = 100 KΩ
R2 = 22 Ω R3 = 1 Ω R4 = 100 Ω R5 = 10 Ω, 1W R6 – R15 = 10 KΩ R16 – R25 = 470 Ω VR1 = 1 MΩ LIN. POT. |
| Capacitors |
| C1 = 220 µF/25V (Electrolytic Capacitor)
C2, C7 = 0.1 µF (Ceramic Disc) C3 = 100 µF/10V (Electrolytic Capacitor) C4, C5 = 100 µF/25V (Electrolytic Capacitor) C6 = 0.0047 µF (Ceramic Disc) C8 = 470 pF (Ceramic Disc) C9 = 1000 µF/25V (Electrolytic Capacitor) C10 = 22 µF/25V (Electrolytic Capacitor) C11 = 10 µF/10V (Electrolytic Capacitor) |
| Semiconductors |
| IC1 = TBA810 (Amplifier IC)
T1 – T10 = BC148B (NPN transistor) D1 – D19 = 1N4148 (rectifier diode) LED1 – LED10 = Any color LED |