One Leveling Amplifier

The IGS ONE LA is an optical compressor, inspired by the legendary solution well known from the '60s. This is a very easy to use and great sounding tool.


The IGS ONE LA is an input and output transformer balanced, full tube device. The input of the system includes an IGS Audio 2510 transformer, the output an IGS 15k/600. Two 6N1P-EW dual-triodes are installed on the audio circuit, while the compression circuit is equipped with the 6N2P-EW triode and the 6AQ5 pentode, which control the work of the T4Bx photocell.

Simply adjust the input Gain and Peak Reduction.


The One LA 19" has simple controls: a Peak-Reduction knob controls the gain of the side-chain circuit, and therefore, the gain reduction threshold; Gain Control for the make-up gain; and a Limit/Compress switch to alter the compression ratio. The VU meter may also be switched to show gain reduction or output level.

It is known that in the case of ONE LA the nature of the device depends on the T4B photo-cell.

T4Bx optocell

The original solution used the TELETRONIX electroluminescent panel, that was illuminating the photo resistor. The idea of opto-compression originated in the past is still being cultivated today. IGS Audio has developed its own photocell equivalent to T4B called T4BX. The use of carefully selected components in the production of the T4BX photocell, and their individual measurement and matching, result in completely repetitive sound qualities of each device.

Stereo pair

Matched pairs are also available. The link socket is located on the rear panel. The RCA-RCA cable is all you need to link two units. Perfect stereo matching is achieved by hand selected tubes and Elma switches.

The One La 19" has a sonic character that makes it sought after by many recording engineers.


  1. Videos
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  3. Specification
  1. Device type
    Optical Compressor Yes, T4Bx or T4B photocell
    Basic features
    Stereo Link Yes, RCA-RCA cable
    All stepped manipulators 24 step Elma switches
    Input & Output
    Input Impedance (balanced) 600 Ohm, IGS Audio custom transformer
    Output Impedance (balanced) 600 Ohm, IGS Audio custom transformer
    Audio transformers IGS Audio custom transformer
    Operating Level +4dBu
    Max input level +16dBu
    Max output level +18dBu
    Dynamic Range >110 dBA (@ 1kHz, +24 dBu)
    Max. gain 30dB
    Max Gain Reduction 36 dB
    Time constants
    Attack: 1ms
    Release: 0.5 – 5s (50% @ 60ms)
    Distortion (@ 20 Hz - 20 kHz)
    THD+N 85 dB (A)
    Voltage 115/230V AC, 50 - 60Hz
    Power consumption 40W
    Power supply Internal
    Packing box
    Dimensions 70 x 50 x 30cm
    Shipping weight 7kg
    Tube set 2x6N1P-EW, 6N2P-EW, 6AQ5
  2. Files
    ONELA manual v1 pdf.pdf