1. Product Overview
The ZK-MT21 and ZK-TB21 are versatile 2.1 channel Bluetooth 5.0 power amplifier modules designed for home and desktop audio systems. They offer both Bluetooth and AUX audio input methods, providing flexible connectivity options for various devices. With dedicated outputs for subwoofer and left/right channels, these modules deliver powerful stereo audio with adjustable bass and treble.
Figure 1: ZK-MT21/ZK-TB21 Bluetooth 5.0 Power Amplifier Module
Video 1: Demonstration of the ZK-TB21 amplifier module connected to speakers and playing music via Bluetooth.
2. What's in the Box
The package typically includes the following components:
Figure 2: ZK-TB21 Package Contents (Assembly Required)
- ZK-TB21/ZK-MT21 Stereo Bluetooth Power Amplifier Module (PCB board)
- Upper cover
- Lower cover
- M2x3mm screws (x8)
- M2x16 copper columns (x4)
- M2x5+4 copper columns (x4)
- Button caps (x5)
- Screwdriver
- Power adapter (DC connector)
Note: The case needs to be assembled by the user.
3. Setup Instructions
3.1 Assembly (if applicable)
If your module came unassembled, follow these general steps to assemble the case:
- Attach the copper columns to the PCB board.
- Secure the lower cover to the PCB board using the appropriate screws.
- Place the upper cover and secure it with the remaining screws.
- Attach the button caps to the control shafts.
3.2 Connections
Refer to the diagrams below for proper wiring and connections.
Figure 3: ZK-MT21 Board Layout and Connections
Figure 4: ZK-TB21 Board Layout and Connections
3.2.1 Speaker Connections
Connect your passive speakers to the amplifier module. Use thicker speaker wires for optimal performance and ease of connection.
- Left Channel Output: Connect to your left speaker.
- Right Channel Output: Connect to your right speaker.
- Subwoofer Output: Connect to your passive subwoofer.
Figure 5: Easy Speaker Connections and Internal Components
3.2.2 Power Supply Connection
The module supports DC 12-24V power input. Ensure your power supply is rated for 5A or above for optimal performance. There are two power input methods:
- 2-Pin Input Socket: For direct wire connection.
- 5.5*2.1MM Socket: For standard DC power adapters.
Connect the power supply to the DC12-24V input terminal on the board. Ensure correct polarity.
Figure 6: Audio Input and Power Supply Methods
3.2.3 Audio Input Connection
The amplifier module supports two audio input methods:
- Bluetooth Input: For wireless connection from devices like phones, tablets, and laptops.
- AUX Input (3.5mm Socket): For wired connection from devices like MP3 players, phones, PCs, or TVs.
Bluetooth mode has priority. If a Bluetooth connection is successful, the module will operate in Bluetooth mode. If Bluetooth is not connected, inserting an AUX cable will switch the module to AUX mode. When using AUX mode, ensure any active Bluetooth connection has been disconnected.
Figure 7: Connecting Your Audio System (ZK-MT21)
Figure 8: Connecting Your Audio System (ZK-TB21)
4. Operation
4.1 Power On/Off
The main volume knob also functions as the power switch. Turn the knob clockwise to power on and increase volume, and counter-clockwise to decrease volume and power off.
4.2 Bluetooth Pairing
- Ensure the amplifier module is powered on.
- On your mobile device (phone, tablet, laptop), enable Bluetooth and search for available devices.
- Select "WZ-BT5.0" (or similar name) from the list to pair.
- Once paired, the module will be ready to receive audio via Bluetooth.
4.3 AUX Input
To use AUX input, ensure no Bluetooth device is actively connected. Plug a 3.5mm audio cable from your source device into the AUX-IN socket on the amplifier module.
4.4 Control Knobs
The amplifier module features several knobs for fine-tuning your audio experience:
- MAIN VOLUME: Adjusts the overall master volume for all channels (left, right, and subwoofer). Turning right increases volume, turning left decreases volume. This knob also acts as the power switch.
- R&L CHANNEL TREBLE: Controls the treble for the left and right channels. Right turn enhances treble, left turn reduces it. Middle position is neutral.
- R&L CHANNEL BASS: Controls the bass for the left and right channels. Right turn increases bass, left turn decreases it. Middle position is neutral.
- SUBWOOFER VOLUME: Controls the volume of the subwoofer. Right turn increases volume, left turn decreases volume.
- SUBWOOFER FREQ (Frequency): Controls the cutoff frequency of the subwoofer (range 20Hz-200Hz). Right turn increases the cutoff frequency, left turn decreases it.
5. Maintenance
To ensure the longevity and optimal performance of your amplifier module:
- Keep the module clean and free from dust. Use a soft, dry cloth for cleaning.
- Avoid exposing the module to moisture, extreme temperatures, or direct sunlight.
- Ensure adequate ventilation around the heat sink to prevent overheating.
- Do not attempt to disassemble or repair the module yourself, as this may void any potential warranty and could cause damage.
6. Troubleshooting
Here are solutions to common issues you might encounter:
6.1 Sound is small, but becomes muddy or distorted when louder.
The sound is distorted. Try lowering the overall volume or changing to a higher voltage adapter power supply. Insufficient input power supply can cause distortion.
Figure 9: Troubleshooting Common Audio Issues (ZK-TB21)
Figure 10: Troubleshooting Common Audio Issues (ZK-MT21)
6.2 Sound is small, but becomes stuck or lags when louder.
This often indicates insufficient input power supply. The power supply itself might be intermittently protected from intermittent power failure. Replace it with a larger power supply. If the power is too high, the power amplifier board may become seriously heated, triggering thermal protection. Reduce power usage or strengthen heat dissipation.
6.3 Factors related to sound quality.
The quality of sound is not only related to the power amplifier module but also to the power supply, audio source, and the entire sound system. Every link in the audio system affects sound quality. Key links include the audio transmission line, audio power supply, tone circuit, power amplifier circuit, speakers, and the surrounding environment. Sound quality is best when the sound source, power supply, power amplifier module, and speakers are well-matched.
Figure 11: Power Source and Speaker Selection Guidance
Figure 12: FAQ on Power Supply and Speaker Selection
7. Specifications
Below are the technical specifications for the ZK-MT21 and ZK-TB21 amplifier modules:
7.1 General Specifications (Both Models)
| Feature | Specification |
|---|---|
| Brand Name | WAPUNO |
| Channels | 3 (2.1) |
| Bluetooth Version | 5.0 |
| Input Sensitivity | 500mV |
| Audio Input | AUX + Bluetooth |
| Adapter Power Supply | DC 12-24V / 5A or above |
| Adapter Speaker | 20-100W, 4-8Ω |
| Output Power (Left/Right) | Max. 50W |
| Output Power (Subwoofer) | Max. 100W |
| Protection Mechanism | Overvoltage, Undervoltage, Overheating, DC detection, Short circuit protection |
| Certification | CE |
7.2 Model-Specific Details
| Feature | ZK-MT21 | ZK-TB21 |
|---|---|---|
| Model Number | ZK-MT21 Amplifier board | ZK-TB21 Amplifier board |
| Amplifier Chip | Domestic power amplifier chip | CS8673E / TPA3116D2 (with AM interference suppression function) |
| Bluetooth Range | Up to 15 meters (unblocked) | Up to 10 meters (no shielding) |
| Protection Mechanism Addendum | - | Anti-reverse connection |
| Product Size (L x W x H) | 93x90x22mm | 118x100x22mm |
| Product Weight (including packaging) | About 185g | About 256g |
Tip: There will be enough output power only when the audio input is sufficient and the power supply voltage/current is sufficient! The higher the power supply voltage, the greater the output power, and the smaller the speaker impedance, the greater the output power! Please make sure that the power of the adapted power supply is greater than the actual working power of the power amplifier!
8. User Tips
- Power Supply Matching: The ripple of the selected power supply is very important. A higher voltage and greater current will result in better sound quality and higher output power. For 3-4 inch speakers, a 12V 1A power supply might be sufficient. For 8-10 inch speakers, a 19V 5A or above power supply is highly valued.
- Speaker Selection: Commonly used speakers are 4-8 ohms. Left and right channels can be connected to full-frequency or mid-high frequency speakers (20-100W). Subwoofers should be connected to subwoofer speakers (20-100W) with a dive frequency of at least 50Hz.
- Preventing Distortion: If the sound is distorted, check your power supply. A weak power supply can cause sound distortion. If the current is too small, sound amplification will be difficult, leading to poor sound quality.
- Heat Management: If the power amplifier board becomes seriously heated, it might be due to excessive power. Reduce power usage or improve heat dissipation to prevent thermal protection from activating.
- Audio Source Quality: Remember that the overall sound quality is a sum of all components. A high-quality audio source will significantly improve the final output.
9. Warranty and Support
For warranty information, technical support, or service inquiries, please contact the seller or manufacturer directly. Keep your purchase receipt as proof of purchase.