IGS – Alter 500
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FET Compressor 1176 Style


  • Series 500 standard Module
  • Input impedance: 1kOhm
  • Output impedance: 600Ω on Carnhill
  • Maximum input level: +20 dBu
  • Maximum Output Level: +22 dBm
  • Total Harmonic Distortion: 0.2%
  • Frequency response: +/- 0.1 dB 20Hz to 20kHz
  • Gain: 40dB- The signal to noise ratio: greater than 99 dB- Attack: 0.02, 0.2 to 0.8 ms
  • Release: 50ms, 600ms, 1.5 s
  • Power supply: + / – 16V

€ 575,
Preise exkl. MwSt.
zuzügl. Versandkosten

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. The compressor is equipped with a relay bypass, achieved 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 discreet API2520 circuit. The level of gain reduction is shown by a 30 point led bar.

Front panel

1. Input – Input level and compression depth
2. Output – Output Level
3. Attack – Variable Attack – 3 ranges: 0.02, 0.2 and 0.8 ms.
4. Release – Amp recovery time to the value of 0.85 max. Range: 50ms, 600ms, 1.5 sec.
5. Ratio – compression ratio over the threshold response.
6. Ratio ranges: from 1:1 (line amp), through 4:1 (compressor) to 20:1 (limiter)7. SLAM – allows the enabling of All-Buttons-On – the “secret weapon” of any studio engineers 😉
8. COMP IN / OUT – Enable Bypass relay device
9. GR – very fast LED indicator showing the compression level in the range from 0 to 30dB.


dB says

When A/B’ing the Alter with an original 1176 the first thing that’s gonna hit you is the claritiy of the IGS Alter.
Also – and very importantly you will find that it’s much less of a “wild horse”, you can actually set it to do what you want it do.

The three settingseach offered for attack / release (slow / medium / fast) got me sceptic at first. But then – thinking about it I realised there’s about 3 positions I use everyday on the real thing. So that works fine for me.

I guess the original version does have more “vibe” to it – it also definitely has more colour of tone.
At the same time – and to my surprise – I must say that I thought the Alter sounded bigger – and I’ll say it again – way clearer.
It’s a bit like having a variation of the 1176 – that at times will or won’t surpass the original, depending on very task at hand.

One thing’s for certain, the Alter is anything but a cheap 1176 clone!!
it has a will of it’s own.