Alter 500

Monophonic FET Limiting Amplifier

The ALTER 500 is a FET compressor built in the 500 standard. 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 settings. 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.

Till this day no better vocal compressor has been designed!

So much stuff inside!

The compressor is equipped with a relay bypass on the front panel. The input is balanced with a modern, low-noise op amp and the output with a Carnhill 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.

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  3. Specification
  1. Device type
    Fet Compressor Yes
    Basic features
    All stepped manipulators Yes
    Input & Output
    Input Impedance (balanced) 10k ohm
    Output Impedance (balanced) 600 ohm, Carnhill transformer
    Audio transformers Yes, Carnhill
    Levels
    Operating Level +4 dBu
    Max input level +20 dBu
    Max output level +22 dBu
    Noise Level -99 dBA
    Max. gain 36 dB
    Max Gain Reduction 20 dB
    Time constants
    Attack: 20us, 400us, 800us
    Ratio 1:1 to 20:1
    Release: 50ms, 600ms, 1.1s
    Bandwidth
    Frequency response 8 Hz to 20 kHz, +/- 0.1dB
    Distortion (@ 20 Hz - 20 kHz)
    THD+N 0.012%
    Power
    Power consumption 2.5W
    Packing box
    Shipping weight 1kg
  2. Files
    IGS ALTER500 user manual.pdf