SoundCraft 1620LE - Manual (Page 28)

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AUX 4 INPUT : BYPASSING MASTER GAIN CONTROLS
The Model 1620’s microphone signals will appear at the tape outputs and effects loop, and will be affected by the house master and tone
controls. In some circumstances, it may be desirable to keep the mic signal from appearing at these points so that it does not get
processed along with the music and is not recorded on tape.
With this modification, the mic connected to AUX 4 will be unaffected by the master gain control. Its level will be controlled only by the
AUX 4 input control. Note, however, that if this modification is done, it is advisable to internally disconnect the line level inputs AUX A –
E from the AUX 4 control, since bypassing the extra tone control and master gain amplification stages will cause the AUX 4 control to
be out of phase with the other AUX controls. If the same line input signal is inadvertently fed from AUX 4 and another AUX control at
the same time, the signal will partially or totally cancel.
To make this modification:
1) Remove the three screws fastening the top cover of the 1620LE to the Chassis, and remove the cover.
2) Move the Mic/Aux4 switch tio the BYPASS position.
3) (Optional but recommend) Locate the front panel circuit board containing the AUX 4/MIC selector switch, and unplug the IDC
connector attached to the ribbon cable. This disables all line level inputs feeding the AUX 4 position.
4) Make sure all connections are secure, and reinstall the top using all three screws.