Calibration procedure for Focusrite ISA 430.
Important : Power up unit and allow to warm up for 15 – 20 minutesVU Meter calibrationSet unit for unity gain and switch to Line Input and select VU InputSet oscillator to +4 dBu 1kHz balanced sine waveTrim PR102 so that the meter needle aligns with 0VUConnect input signal to Insert Return , select VU Ins Ret and check that needle is still aligned with 0VUCompressor CalibrationVCA Offset TrimWith no input signal , trim PR4 for 0mV at the VCA offset test point located on the underside of the lower PCB adjacent to the Make Up Gain pot P100RatioSet unit for unity gain and switch to Line InputSet oscillator to +20 dBu 1kHz balanced sine waveSet all Compressor controls CCW and switch on compressorTrim PR1 ( underside of lower PCB ) for DUT output of +4dBuSet ratio control fully CW . DUT output should be -20dBuGain Change Meter CalibrationNote that the silk screen is incorrect and PR100 trims for zero gain reduction and PR101 trims for -10 gain reduction .Set unit for unity gain and switch to Line Input and select VU Com G/CSet oscillator to +4 dBu 1kHz balanced sine waveSet all compressor controls fully CCW and switch on compressor . Adjust the ratio control for a DUT output of -6dBu ( 10dB of gain reduction ) .Mute the oscillator and trim PR100 so that the meter needle is aligned with 0VU .Un-mute the oscillator and trim PR101 so the meter aligns with -10VU .Repeat the process until the meter lines up with zero gain reduction and -10dB gain reduction .Gate CalibrationGate SymmetrySet oscillator output level to -10dBuSet Line gain and trim to 0dBTrim PR3 ( under Con 3 ribbon cable ) for a symmetrical waveform at the G Sym test point located on the underside of the lower PCB adjacent to the Gate Threshold pot P106 .Gate ThresholdSet oscillator output to -40dBuSet Range fully CW . All other gate controls fully ACWSet Line gain to 0dBSet trim to 0Adjust PR2 ( under Con 3 ribbon cable ) until the gate closes
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