CUQI ZK-HT21 Bluetooth Amplifier Board User Manual

1. Introduction

The CUQI ZK-HT21 is a 2.1 channel Bluetooth amplifier board designed for DIY speaker projects. It features Bluetooth 5.0 connectivity, AUX, and USB input options, delivering 160W for left and right channels and 220W for the subwoofer. This amplifier board includes independent treble and bass controls for precise audio adjustment and incorporates multiple protection mechanisms for safe operation.

Image 1.1: CUQI ZK-HT21 Bluetooth Amplifier Board overview.

2. Package Contents and Component Identification

2.1 Package Contents

The package includes the following items:

• Bluetooth Amplifier Board
• Top cover plate
• Lower cover plate
• Power terminal
• M2x4mm Screws (x8)
• M2x18 Copper Columns (x4)
• M2x5+4 Copper Columns (x4)
• Button caps (x5)
• Screwdriver

Image 2.1: Contents included with the ZK-HT21 amplifier board.

2.2 Component Identification

Familiarize yourself with the various components and their functions on the amplifier board:

Image 2.2: Detailed view of the ZK-HT21 amplifier board with labeled components.

• Power Input: 5.5x2.1DC Header and 2P Terminal for DC 15-36V power supply.
• Left/Right Bass Channel: Speaker output terminals.
• Bluetooth Input: Wireless audio connection.
• AUX Audio Input: 3.5mm jack for wired audio.
• Antenna Base: For Bluetooth antenna (can be directly welded or use the antenna base).
• Filter Appliances: Components for signal conditioning.
• Super Long Life Quiet Fan: For heat dissipation.
• Large Capacity Energy Storage Capacitor: For stable power delivery.
• Low Noise Pre-Op Amp: For signal amplification.
• USB Input Interface: For USB audio input (U-Disk).
• Subwoofer Frequency (FREQ) Knob: Adjusts subwoofer cutoff frequency.
• Bass Volume Knob: Adjusts subwoofer volume.
• Left and Right Channel Treble Knob: Adjusts high frequencies for main channels.
• Left and Right Channel Bass Knob: Adjusts low frequencies for main channels.
• Master Volume/Switch Knob: Controls overall volume and power on/off. Press for short actions (pause/play), long press for mode switching (USB/Bluetooth/AUX).

3. Setup Instructions

3.1 Assembly

Follow these steps to assemble the amplifier board:

1. Place the PCB board on the lower cover plate, aligning the screw holes.
2. Secure the PCB board to the lower cover plate using the M2x5+4 copper columns.
3. Attach the top cover plate to the PCB board using the M2x18 copper columns.
4. Secure the top cover plate with the M2x4mm screws.
5. Install the button caps onto the control shafts.
6. Connect the power terminal to the designated power input on the board.

Image 3.1: Exploded view illustrating the assembly process of the amplifier board.

3.2 Power Connection

The amplifier board supports DC 15-36V power supplies. Connect a compatible power adapter to the power input header or terminal. Ensure correct polarity to prevent damage. The board triggers under-voltage protection below 9V.

3.3 Speaker Connection

Connect your speakers to the appropriate terminals:

• Connect the subwoofer to the "SUBWOOFER" output terminals.
• Connect the left channel speaker to the "L" output terminals.
• Connect the right channel speaker to the "R" output terminals.

This amplifier is compatible with 30–200W, 4–8Ω speakers.

4. Operating Instructions

4.1 Power On/Off and Mode Selection

• Power On/Off: Rotate the Master Volume/Switch knob clockwise to turn on the amplifier. Rotate counter-clockwise until it clicks to turn off.
• Mode Selection: Long press the Master Volume/Switch knob to cycle through input modes: Bluetooth, USB, and AUX.

4.2 Audio Input Methods

The ZK-HT21 amplifier board supports three audio input methods:

Image 4.1: Overview of available audio input methods.

1. Bluetooth Connection:
   • Ensure the amplifier is in Bluetooth mode (indicated by the blue LED).
   • On your audio device (phone, tablet, laptop), search for Bluetooth devices and select "ZK-HT21".
   • Once paired, audio will stream wirelessly. The Bluetooth connection range is approximately 15 meters (49 feet).
2. AUX Connection:
   • Connect your audio device (phone, PC, MP3 player, TV) to the 3.5mm AUX input jack using an audio cable.
   • Switch the amplifier to AUX mode.
   • Note: When using AUX mode, ensure any active Bluetooth connection to the module is disconnected.
3. USB (U-Disk) Connection:
   • Insert a USB flash drive (U-Disk) containing audio files into the USB input interface.
   • Switch the amplifier to USB mode. The amplifier will automatically play audio files from the U-Disk.

4.3 Audio Control Knobs

• Subwoofer Frequency (FREQ): Adjusts the crossover frequency for the subwoofer.
• Bass Volume: Controls the output volume of the subwoofer.
• Left and Right Channel Treble: Adjusts the high-frequency response for the main stereo channels.
• Left and Right Channel Bass: Adjusts the low-frequency response for the main stereo channels.
• Master Volume/Switch: Controls the overall output volume. Short press acts as play/pause. Long press cycles input modes.

5. Specifications

Image 5.1: Physical dimensions of the ZK-HT21 amplifier board.

6. Safety and Protection Features

The ZK-HT21 amplifier board is equipped with multiple built-in protection features to ensure safe and reliable operation:

• Reverse Polarity Protection: Prevents damage if the power supply is connected incorrectly.
• Short Circuit Protection: Safeguards against damage from short circuits in the speaker outputs.
• Overheating Protection: The integrated silent fan and thermal management prevent the board from exceeding safe operating temperatures.
• Overcurrent Protection: Protects components from excessive current draw.
• Under-voltage Protection: The board will trigger protection if the input voltage drops below 9V.

Image 6.1: Visual representation of the amplifier board's protection and heat dissipation mechanisms.

7. Troubleshooting

If you encounter issues with your ZK-HT21 amplifier board, refer to the following common problems and solutions:

• No Sound Output:
  • Ensure the amplifier is powered on and the master volume is turned up.
  • Verify that speakers are correctly connected to the output terminals.
  • Check the audio input source and cable connections.
  • Confirm the correct input mode (Bluetooth, AUX, USB) is selected.
  • If using AUX, ensure Bluetooth is disconnected from the module.
• Distorted Sound:
  • Reduce the master volume or the volume from your audio source.
  • Check speaker impedance and power compatibility (4-8Ω, 30-200W).
  • Ensure all connections are secure and free from interference.
  • Adjust the treble and bass controls to a neutral position and re-evaluate.
• Bluetooth Pairing Issues:
  • Ensure the amplifier is in Bluetooth mode.
  • Make sure the amplifier is within the 15-meter Bluetooth range of your device.
  • Disconnect any other devices currently paired with the amplifier.
  • Try restarting both the amplifier and your Bluetooth device.
• Amplifier Not Powering On:
  • Verify the power supply is connected correctly and providing DC 15-36V.
  • Check the power adapter for functionality.
  • Ensure the master volume knob is rotated clockwise past the "off" click.

8. Maintenance

To ensure the longevity and optimal performance of your ZK-HT21 amplifier board, follow these maintenance guidelines:

• Cleaning: Use a soft, dry cloth to gently wipe the surface of the amplifier board. Avoid using liquid cleaners or solvents, as they may damage the electronic components.
• Ventilation: Ensure the fan and ventilation openings are clear of dust and obstructions to maintain effective heat dissipation. Periodically clean any accumulated dust.
• Storage: When not in use for extended periods, store the amplifier board in a cool, dry place away from direct sunlight and extreme temperatures.
• Handling: Handle the board with care to avoid physical damage to components or connections.

9. Warranty and Support

For warranty information and technical support, please refer to the documentation provided at the time of purchase or contact the seller directly. Keep your purchase receipt as proof of purchase.