Edition:
07.02.01E 3/16 Alignment, general
928 Mixing Console
3.2.8 Demagnetizing the input transformers
• Prohibited connection of unbalanced input sources or unintentional
shorting of the A and/or B audio line of the microphone inputs to chas-
sis when phantom supply is active can drive the input transformers
into saturation and cause permanent magnetization (remanence). This
manifests itself in the form of significantly higher harmonic distortion
and microphonic noise: Light mechanical action on the mixing con-
sole, as tapping, causes an audible modulation via the outputs even
when the microphone inputs are not active.
• Remanence can also accumulate over extended operating periods.
• All microphone inputs should, therefore, be demagnetized periodi-
cally and prior to calibration.
Procedure: • Switch the console off.
• Feed a frequency of < 32 Hz to one microphone input after the other.
• Increase the generator level from 0 V to about 3 V.
• Continuously reduce the level very slowly to 0 V.
f < 32 Hz,
U: 0 V...3 V.........0 V
1000 µF/10 V
600
Ω
2
3
MIC INPUT
A
B
AF Generator
R 50
Ω
Capacitor (1000 µF/10 V) blocks any DC component
Resistor (600 Ω) is used for discharging the capacitor
To Next Page
Loading...
