The IGS A-Type 500 compressor/limiter is inspired by a legendary American design from the 1970s. The circuit is built entirely with discrete components in a through-hole assembly. The compressor input is balanced by the SSM2141 op-amp, while the output is transformer-balanced. An additional, second audio transformer is responsible for the feedback signal, which, after adjusting the time constants, returns to the compression control element, the VCR (Voltage Controlled Resistor). The control signal has a negative value relative to the circuit ground, and its value directly affects the VCR resistance, which in turn adjusts the gain of the first amplification stage.
The compressor is equipped with a unique set of controls, including a „Compress” switch that simultaneously changes both Gain and Threshold values. This allows you to adjust compression parameters while maintaining constant peak signal levels. Additionally, separate Threshold and Output knobs allow for precise control over the compressor’s activation point and output signal.
The device offers two modes of operation: Compressor (2:1) and Limiter (20:1). The Attack time is fixed and very fast at 15μs. The Release time can be set to one of four options: 0.1s, 0.5s, 1.5s, and 2.0s. An additional mode is the de-esser, designed to reduce sibilance in vocal recordings.
Input & Output
• Audio transformers: Yes, IGS custom transformers
• Input Impedance (balanced): 10k, SSM2141
• Output Impedance (balanced): 75 Ohm, IGS custom transformer
Levels
• Operating Level: +4 dBu
• Max input level: +27 dBu
• Max output level: +28 dBu
• Max Gain Reduction: -25 dB
• Max. gain: 25 dB
• Noise Level: -99 dBA
Time constants
• Attack: 15us
• Release: 100ms - 2s
• Ratio: 2:1, 20:1
Bandwidth
• Frequency response: 8 Hz to 20 kHz, +/- 0.1dB
Distortion (@ 20 Hz - 20 kHz)
• THD+N: 0.014%
Power
• Power consumption: 2.5W
Packing box
• Shipping weight: 1kg
