IGS Audio Alter

FET Limiting Amplifier
The ALTER 500 is a FET compressor built in the 500 standards. The FET-type solution was used for the first its application in the legendary UREI 1176 compressor from the 70s. The ALTER is a single-channel unit with stepped input and output controls. The Ratio switch has six positions, including two additional to the original 1176 1:1 and 2:1 setting. Slam Mode can be turned on with a separate switch, working regardless of the Ratio settings. Attack and release times can be set to Fast / Mid / Slow with 3-pole switches.

So much stuff inside!
The compressor is equipped with a relay bypass switch on the front panel. The input is balanced with a modern, low-noise op-amp and the output with an IGS Custom transformer. The circuit has two-amp stages, between which is the output control. The stage amps are based on the discrete 990 circuit. The level of gain reduction is shown by a 20-point led bar.