ZK-LT21 Bluetooth 5.1 Digital Power Amplifier Board Module User Manual

1. Introduction

The ZK-LT21 is a versatile 2.1 channel digital power amplifier board module featuring Bluetooth 5.1 connectivity, designed to deliver 15W per stereo channel and 30W for a subwoofer. This module offers multiple audio input options including Bluetooth, AUX, USB flash disk, and USB sound card. It supports the Wuzhi Audio APP for advanced control and customization, making it suitable for a wide range of audio applications.

2. Specifications

Note: It is recommended to use an 8Ω speaker and a 9-24VDC power supply. Overpressure is not allowed. If driving a 4Ω speaker, the power supply should not exceed 12V.

3. Setup

3.1 Assembly

The amplifier board module comes unassembled and requires self-assembly of the protective shell. Follow the diagram below for proper assembly:

1. Place the PCB (Printed Circuit Board) onto the lower cover board.
2. Secure the PCB using the M2*3+3 copper pillars and M2*3 screws.
3. Attach the upper cover board.
4. Install the volume knobs onto the potentiometers.
5. Use the provided screwdriver and DC power adapter cable for convenience.

3.2 Wiring Connections

Refer to the function introduction diagram for correct wiring of power, audio input, and speaker outputs.

• Power Input (DC9-24V): Connect a DC power supply within the specified voltage range to the DC9-24V terminal. Ensure the polarity is correct (+ and -). Do NOT connect to AC power.
• AUX Input: Use a 3.5mm audio cable to connect an external audio source (e.g., phone, MP3 player) to the AUX-IN jack.
• USB Flash Disk / USB Sound Card Input: Insert a USB flash drive into the USB port for direct playback, or connect to a computer via USB to use the module as a USB sound card.
• Left Channel Speaker Output: Connect your left channel speaker to the 'L' terminals.
• Right Channel Speaker Output: Connect your right channel speaker to the 'R' terminals.
• Subwoofer Speaker Output: Connect your subwoofer to the 'S' terminals.

4. Operating Instructions

4.1 Power On/Off

The module features a classic mechanical switch integrated with the volume knob. Simply turn the knob to power on or off. There is no need for a long press; a single turn will activate or deactivate the device. A 'pop' sound may be heard when starting or shutting down.

4.2 Volume Adjustment

The module has two independent volume knobs:

• Volume R&L Channel: Adjusts the volume for the left and right stereo channels.
• Volume Subwoofer: Adjusts the volume specifically for the subwoofer channel.

Both are classic mechanical knobs with a volume scale, offering stepless adjustment for precise control.

4.3 Audio Input Selection

The module automatically detects and switches between audio inputs. Prioritize Bluetooth for wireless connection, or use AUX/USB for wired sources.

• Bluetooth: Pair your device with the amplifier module via Bluetooth 5.1.
• AUX: Connect an audio source using a 3.5mm cable.
• USB: Insert a USB flash drive for music playback or connect to a computer for USB sound card functionality.

5. Wuzhi Audio APP Features

The ZK-LT21 supports the Wuzhi Audio APP, providing enhanced control and customization options for your audio experience. The APP allows you to:

• Modify Bluetooth Name: Easily change the Bluetooth name of your module for better identification, especially when using multiple devices.
• Set Bluetooth Password: Enhance security by setting a password for Bluetooth connections, preventing unauthorized access. This feature can be toggled on or off.
• Adjust Prompt Tone Volume: Customize the volume of system prompt sounds to your preference.
• On/Off Prompt Tone: Enable or disable prompt tones as needed.
• Sleep Aid (Lullaby) Function: Access a selection of natural sounds (up to 1023 combinations) to create a relaxing atmosphere for sleep. The APP includes a timed shutdown function for this feature.

• Sound Effect Selection + Custom Sound Effect: Choose from various preset sound effects or utilize the custom 10-segment equalizer to fine-tune audio output, optimizing sound for different speakers and preferences.

• USB Flash Disk Playlist: Manage and play music directly from a USB flash drive, with support for track skipping and shuffling.

5.1 Bluetooth Name Modification Steps (via APP)

1. Enter a new Bluetooth name in the APP.
2. Click the 'Set' button.
3. The system will automatically restart.
4. Cancel pairing of your mobile device with the old Bluetooth name.
5. Find the new Bluetooth name and re-pair.

5.2 Bluetooth Password Setting Steps (via APP)

Method 1:

1. Turn on the Bluetooth password switch in the APP.
2. Use the default password '1111'.

Method 2:

1. Turn on the Bluetooth password switch in the APP.
2. Enter your desired password.
3. Click the 'Setting' button.
4. The system will restart automatically.
5. Cancel pairing, and you will be prompted to enter the new password when connecting again.

6. Maintenance

• Keep the amplifier module dry and away from moisture to prevent damage.
• Clean the module gently with a dry, soft cloth. Avoid using harsh chemicals or abrasive materials.
• Ensure proper ventilation around the module to prevent overheating.
• Avoid exposing the module to extreme temperatures or direct sunlight.
• Disconnect power before cleaning or performing any maintenance.

7. Troubleshooting

• No Sound:
  • Check if the power supply is correctly connected and within the specified voltage range (DC 9-24V).
  • Ensure all speaker wires are securely connected to the correct terminals and that speaker polarity is observed.
  • Verify that the audio input source (Bluetooth, AUX, USB) is active and properly selected.
  • Check if the volume knobs for both R&L channels and the subwoofer are turned up.
• Distorted Sound:
  • Ensure the power supply voltage is stable and not exceeding 24V (or 12V for 4Ω speakers).
  • Verify that the connected speakers' impedance matches the recommended 4-8Ω.
  • Reduce the input volume from your audio source or the amplifier's volume knobs.
  • Check for loose connections or damaged cables.
• Bluetooth Connection Issues:
  • Make sure the amplifier module is powered on and within range of your Bluetooth device.
  • Try forgetting the device in your phone's Bluetooth settings and re-pairing.
  • If a Bluetooth password is set, ensure you are entering the correct one.
  • Restart both the amplifier module and your Bluetooth device.
• Wuzhi Audio APP Issues:
  • Ensure you have the correct Wuzhi Audio APP installed.
  • Check for APP updates.
  • Verify your mobile device's compatibility with the APP.
  • Restart the APP or your mobile device.

8. User Tips

• Power Supply Quality: Using a stable and clean power supply (e.g., a good quality regulated DC adapter) is crucial for optimal sound performance and to prevent noise.
• Speaker Matching: Always match your speaker impedance to the amplifier's recommendations (4-8Ω). Using speakers with too low impedance can damage the amplifier, especially at higher volumes.
• Cable Quality: Invest in good quality audio cables and speaker wires to minimize signal loss and interference.
• APP Customization: Explore the Wuzhi Audio APP's custom sound effect feature to tailor the audio output to your specific speakers and listening environment. This can significantly improve sound quality.
• Heat Management: While the module has overheating protection, ensuring good airflow around the board, especially when driving demanding speakers or at high volumes, can prolong its lifespan.

9. Package Contents

The package typically includes the following items:

• 1x ZK-LT21 Digital Power Amplifier Board Module
• 1x Screwdriver
• 1x DC Power Adapter Cable
• Set of M2*3 screws, M2*16 copper pillars, M2*3+3 copper pillars for assembly

10. Safety Information

• Always ensure the power supply is disconnected before making any wiring changes or performing maintenance.
• Use only a DC power supply within the specified voltage range (9-24V). Connecting to AC power or an incorrect DC voltage can damage the module and pose a safety risk.
• Ensure correct polarity when connecting the power supply.
• Avoid short circuits between terminals.
• Do not operate the module in wet or damp conditions.
• Keep out of reach of children.
• If driving 4Ω speakers, ensure the power supply does not exceed 12V to prevent damage.

11. Warranty and Support

For any issues, technical support, or warranty claims, please contact the seller or manufacturer directly. Retain your purchase receipt for proof of purchase.