The power amplifier board provides a CTRL input that is normally connected to the Bluetooth MUTE pin, enabling coordinated mute control with Bluetooth audio modules. By default the board operates in ACF1 mode. To enable CTRL mode, remove the solder bridge on R5. Key benefits Simplified mute control: integrates directly with Bluetooth modules that expose a MUTE signal, enabling synchronized muting of the amplifier. Flexible mode selection: ships in ACF1 mode and can be switched to CTRL mode as needed. Easy mode change: switch modes by modifying the R5 resistor (solder off) without needing extra components. Function and compatibility CTRL pin is designed to interface with the MUTE pin on Bluetooth devices, allowing direct control of the amplifier's mute state from the Bluetooth module. Default configuration is ACF1 mode; CTRL mode is available by removing R5. Mode details ACF1 mode: standard factory default operation. CTRL mode: enabled by removing R5, allowing CTRLbased control via the CTRL pin to manage the Bluetooth MUTE signal. How to configure To use CTRL mode: set CTRL mode by soldering R5 off (remove the resistor bridge). To to default ACF1 mode: restore R5 if needed per the board's configuration guide. Use scenarios Bluetooth speaker assembly: wire the CTRL pin to the Bluetooth MUTE output to ensure the amplifier muting aligns with Bluetooth playback state. Car audio upgrade: connect the CTRL pin to the car's Bluetooth module MUTE signal for consistent muting behavior during media switching. Embedded audio project: drive the CTRL input from a microcontroller or external control signal to manage mute independently of the Bluetooth module when needed. Notes Physical size, material, and exact pin layout depend on the specific board variant; refer to the product datasheet for dimensions and material details. This description reflects the stated default and CTRLmode configuration possibilities without altering other specifications of the board.