Peak level indicator
Understanding Audio Signal Levels
The peak level, representing the instantaneous measurement of the audio level, holds significance in gauging the highest point of the audio and its proximity to the ceiling, donating the maximum permissible level before distortion occurs. On the other hand, the average level serves as a metric for the average energy sustained over a specified time interval.
Peak Level Indicator Circuit:
This circuit incorporates two comparators, IC1a and IC1b, designed to function as a peak-level indicator for each channel in a stereo audio system. The comparators operate with a reference voltage range of 0–1 V applied to their non-inverting inputs through P1 and P2, respectively. To ensure that the reference voltage stays within the common mode range of the op-amps, resistor R3 is employed in the circuit. The indicator utilizes two LEDs to visually signal when the signal level surpasses the predetermined threshold in either channel.
Part List
- R1=1Mohms
- TR1=1Mohms trimmer
- C1=100nF, 100V, MKT
- C2 = 150 nF, 100V, MKT
- D1-2-3=1N4148
- D4=RED LED DIODE
- IC1=74C14
Rectilinear Peak Level Indicator Circuit:
The signals originating from the two audio channels undergo rectilinear feeding (half-wave) through Di and D2. The resultant direct voltage is then directed to the inverting inputs of the operational amplifiers. Given the low input impedance ranging from 200 to 300 ohms, the voltage drop across the diodes is kept minimal at 0 mV. Resistor R1 and R2 function to restrict input current in cases where drive levels exceed the common mode range. When the input signal’s peak value triggers a drop across the diode, the corresponding opamp undergoes a change in state (goes low), leading to the illumination of the associated LED.
The circuit exhibits functionality up to 20 kHz, accommodating variations in peak levels within ±0.25 dB. The indicator’s current consumption stands at a mere 0.25 mA when the LEDs are inactive and increases to 24 mA when both LEDs illuminate. The utilization of high-efficiency LEDs, drawing only 2–3 mA, offers the potential to reduce this drain, necessitating an adjustment in the values of R4 and R5 to 3.3 kΩ.
Notes:
- It can be assembled on a general-purpose PCB.
- It can be powered by a 12V–15V regulated power supply.