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Compressor or Limiter Schematic Circuit Diagram

Distinguishing Compressor and Limiter:

Compressor or limiter. In the audio realm, a compressor operates with a low ratio, selectively attenuating some volume when surpassing the predetermined threshold. Conversely, a limiter employs a substantial ratio, effectively reducing all volumes that exceed the specified threshold.

Compressor or Limiter Circuit:

The circuitry of the compressor is constructed around two sequentially connected attenuator networks. These networks achieve attenuation through the utilization of light-dependent resistors (LDRs) exposed to illumination from light-emitting diodes (LEDs).

The input signal is directed to the non-inverting input of opamp IC1a via R1. In conjunction with D3, D4, and IC1b, IC1a executes full-wave rectification of the incoming signal. The resulting direct voltage is harnessed to charge capacitor C5 through D5, with the diode facilitating rapid charging while the capacitor can only discharge via R7.

Compressor or limiter Schematic diagram

Compression Control Circuit Operation:

The core compression function is executed by IC1c. Depending on the configurations of P1 and P2, IC1c’s output voltage decreases as the potential across C5 reaches a specific threshold. This action prompts T2 and, via IC1d, T1 to conduct, leading to the illumination of LEDs and subsequent attenuation of the input signal. The circuit’s attack time is governed by the speed of the LDRs and the adjustment of P2.

Voltage Limiting and Amplification:

The initiation of voltage-limiting is determined by the amplification of IC1c and the setting of P1. The output voltage remains constant when the input signal surpasses a certain level until the current through the LEDs reaches its maximum (approximately 40 mA). In its current configuration, the circuit functions as a limiter; however, connecting the +ve input of IC1a to the circuit’s output transforms it into a standard compressor.

Signal Processing Range and Circuit Characteristics:

The circuit effectively processes signals within the range of approximately 10 mV r.m.s. to 2 V r.m.s. To extend this range, additional attenuator sections can be incorporated, or the values of R1 and R2 can be increased. Ensuring a light-tight enclosure for the LDR/LED combinations is crucial. The circuit’s current draw is predominantly dictated by the LEDs and does not exceed 50 mA. It’s essential to note that compression, while capable of reducing dynamic range, can be a valuable tool when applied judiciously to enhance a mix.

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