If you experience crackling audio or intermittent signal loss when turning a knob or pressing a button: Power down the console. Remove the module channel strip if possible.
The Complete Guide to the Amek 501 Langley Mixing Console: Operations, Maintenance, and Legacy Amek 501 Langley Manual
He looked back at the manual, specifically the final page where the original engineer had written a single note in permanent marker: If you experience crackling audio or intermittent signal
Toggles between the ultra-low-noise microphone preamplifier (featuring custom input transformers) and the balanced line-level input. Amek 501 Langley Manual
Many consoles were paired with the Amek SuperTrue automation system, allowing fader and mute automation. 2. Amek 501 Langley Technical Specifications