CA-502MT (ZK-502MT) 50W+50W Bluetooth 5.0 Audio Amplifier Board

Key Features

• 2.0-channel stereo amplifier

• Maximum 50W + 50W output

• Bluetooth 5.0 wireless audio

• Up to approximately 15m wireless range in open conditions

• 3.5mm AUX wired input

• Independent bass control

• Independent treble control

• Integrated master volume control

• DC 9V–24V input

• 4Ω–8Ω speaker compatibility

• 15W–100W recommended speaker range

• 
  

  90dB signal-to-noise ratio

• Compact PCB design

• Aluminium heat sink

• Overheat protection

• Overcurrent protection

• Short-circuit protection

• Protective acrylic shell

• Suitable for compact DIY audio projects

Technical Specifications

Amplifier

Power Supply

Output Power vs Supply & Speaker Load

Speaker Compatibility

Audio Inputs

Sound Controls

The ZK-502MT provides three physical controls:

• Treble

• Bass

• Master Volume

This allows basic tone adjustment directly from the amplifier module.

Protection Functions

Published protection mechanisms include:

• Overheat protection

• Overcurrent protection

• Short-circuit protection

Physical Specifications

Important Power Output Note

The 50W + 50W specification is achieved under the published high-output condition of approximately:

24V DC + 4Ω Speakers

The amplifier does not deliver 50W per channel at every voltage or speaker impedance.

For example, using a 12V supply substantially reduces the available output power.

Compatibility

Speaker Compatibility

The ZK-502MT is designed for passive stereo speakers within:

4Ω–8Ω

Published recommended speaker power range:

15W–100W

A typical system consists of:

• 1 × Left Passive Speaker

• 1 × Right Passive Speaker

Power Supply Compatibility

Supported power range:

DC 9V–24V

Minimum recommended supply capability:

3A or above

For higher-output applications, RoboGears recommends:

24V DC / 5A

with suitable 4Ω speakers.

Common Power Supply Options

Depending on the required output level, the amplifier can be used with suitable regulated:

• 12V DC supplies

• 15V DC supplies

• 19V DC laptop-style adapters

• 24V DC supplies

Higher voltage does not automatically mean better results unless the power supply also has sufficient current capacity.

Never exceed 24V DC.

Audio Source Compatibility

The module supports:

Bluetooth

Suitable for compatible:

• Smartphones

• Tablets

• Laptops

• Computers

• Bluetooth audio sources

AUX

The standard 3.5mm AUX input can be used with compatible:

• Computers

• TVs with analogue audio output

• MP3 players

• Audio decoder boards

• Smartphones with suitable audio output/adaptor

• Other line-level audio sources

Required for a Complete System

You will generally need:

• Suitable DC power supply

• Left passive speaker

• Right passive speaker

• Speaker wires

• Bluetooth or AUX audio source

For AUX operation, a suitable 3.5mm audio cable is also required.

Before Purchase

Check Your Speakers

Recommended:

4Ω–8Ω / 15W–100W

Check Your Power Supply

For maximum advertised output:

24V DC + Adequate Current + 4Ω Speakers

are required.

Understand the Channel Configuration

This is a:

2.0 Stereo Amplifier

It provides:

• Left channel

• Right channel

It does not provide a dedicated amplified subwoofer channel.

Applications

• DIY Bluetooth speakers

• Desktop stereo speakers

• Bookshelf speaker projects

• Multimedia audio systems

• DIY home audio

• Wireless speaker projects

• Portable speaker projects

• Computer speakers

• Workshop audio systems

• Custom amplifier boxes

• Audio electronics projects

• Educational amplifier projects

• Compact stereo systems

• Bluetooth audio upgrades

• DIY wooden speaker cabinets

Suitable For

• DIY audio enthusiasts

• Electronics hobbyists

• Speaker builders

• Students

• Audio technicians

• Makers

• Electronics laboratories

• Compact amplifier projects

📦 What's Included

❌ What's Not Included

Unless specifically supplied as part of another bundle, the standard package does not include:

• DC Power Supply / SMPS

• Left Speaker

• Right Speaker

• Subwoofer

• Speaker Wire

• AUX Cable

• Smartphone / Audio Source

• External Bluetooth Antenna

• Complete Speaker Cabinet

• AC Power Cable

Important Purchase Note

This is a DIY stereo amplifier module, not a complete ready-to-use Bluetooth speaker system.

To create a working stereo system, you will generally need:

DC Power Supply + ZK-502MT + Left Passive Speaker + Right Passive Speaker + Audio Source

Assembly Note

The protective shell requires basic assembly.

Before applying power:

• Install the PCB securely

• Fit the control knobs

• Ensure mounting hardware does not short the PCB

• Keep the heat sink exposed to airflow

• Check all terminal connections

Product Variation

PCB colour, heat-sink appearance, knob style, protective-shell design and individual component brands may vary slightly between manufacturing batches while maintaining the intended product functionality.

Getting Started

Step 1 — Identify the Connections

Before applying power, identify:

• DC power input

• Left speaker output

• Right speaker output

• 3.5mm AUX input

• Bluetooth section

• Treble control

• Bass control

• Volume / Power control

Always follow the labels printed on the actual PCB.

Step 2 — Assemble the Protective Shell

Install:

• Upper cover

• Lower cover

• Copper pillars

• Screws

• Control knobs

Ensure that no metal mounting hardware contacts unintended PCB tracks or components.

Step 3 — Select the Power Supply

Supported range:

DC 9V–24V

Use a regulated supply capable of providing sufficient current.

For higher-power operation:

24V DC / 5A

is recommended.

Never exceed 24V DC.

Step 4 — Connect the Speakers

Connect:

Left Passive Speaker → Left Output

Right Passive Speaker → Right Output

Use suitable:

4Ω–8Ω speakers

Step 5 — Check Speaker Wiring

Before applying power:

• Check positive/negative speaker connections

• Ensure no loose strands are touching

• Prevent output-terminal short circuits

• Secure the terminals properly

Step 6 — Turn the Volume Down

Before first startup, turn the master volume down.

Keep bass and treble near their neutral positions initially.

Step 7 — Connect Power

Verify:

• Correct DC voltage

• Correct polarity

• Secure connection

• No short circuits

Then switch the amplifier on.

Step 8 — Bluetooth Connection

For Bluetooth operation:

1. Disconnect AUX if necessary

2. Power on the amplifier

3. Enable Bluetooth on your phone/tablet/computer

4. Search for available Bluetooth devices

5. Select ZK-502MT

6. Complete pairing

7. Begin playback at low volume

Step 9 — AUX Connection

Connect a standard 3.5mm audio cable to the AUX input.

If Bluetooth is connected simultaneously, disconnect Bluetooth if required to prevent input conflicts.

Step 10 — Test the Stereo Channels

At low volume confirm:

• Left channel

• Right channel

• Bass control

• Treble control

• Master volume

Step 11 — Increase Volume Gradually

Increase the level while monitoring:

• Sound quality

• Speaker movement

• Heat-sink temperature

• Power-supply stability

Basic System Layout

Bluetooth Smartphone / AUX Source

↓

ZK-502MT

↓

Left Passive Speaker + Right Passive Speaker

and

9V–24V DC Power Supply → ZK-502MT

For Maximum Advertised Output

The published 50W + 50W condition requires approximately:

24V DC + 4Ω Speakers + Adequate Power-Supply Current

Using a lower-voltage supply will reduce the available maximum output.

🔧 Prototyping and Engineering Tips from RoboGears

1. Match the Power Supply to the Required Output

The ZK-502MT's output changes substantially with supply voltage.

For example:

12V + 4Ω → Approx. 20W + 20W

19V + 4Ω → Approx. 40W + 40W

24V + 4Ω → Approx. 50W + 50W

Choose the supply according to the output you actually need.

2. Use 24V for Maximum Advertised Output

To approach the maximum:

50W + 50W

rating, use a suitable 24V regulated power supply with sufficient current and compatible 4Ω speakers.

3. Do Not Use an Unregulated 24V Battery Pack

The published documentation specifically warns against directly using a nominal 24V battery pack because its fully charged voltage may exceed the amplifier's maximum permitted input.

Use a properly regulated supply within the specified voltage range.

4. Don't Expect 100W From a 12V Adapter

The 50W-per-channel figure is not available across the entire voltage range.

A 12V supply produces substantially lower maximum output.

5. Match Speaker Impedance

Use:

4Ω–8Ω passive speakers

Do not connect loads below the specified impedance range.

6. Avoid Excessive Bass at Maximum Volume

Heavy bass requires substantial peak power.

If distortion appears when bass and volume are high:

• Reduce bass

• Reduce volume

• Check power-supply capacity

7. Use a Clean Power Supply

Poor-quality switching supplies can introduce:

• Hum

• Buzz

• High-frequency noise

• Bluetooth interference

A good regulated DC supply can significantly improve the finished system.

8. Keep AUX Wiring Away From Power Wiring

Route low-level audio wiring away from:

• DC input cables

• Speaker output wires

• Switching power circuitry

This can reduce noise pickup.

9. Maintain Airflow Around the Heat Sink

Do not completely cover the amplifier or heat sink inside a sealed enclosure.

Provide ventilation for continuous higher-output use.

10. Bluetooth Range Depends on Installation

The published open-area range is approximately 15m.

Actual range may decrease because of:

• Walls

• Interference

• Metal enclosures

• Poor antenna positioning

11. External Antenna Modification Is Possible

Some ZK-502MT board revisions provide a solder point for an external Bluetooth antenna.

This is an advanced modification and the external antenna itself is not part of the standard package.

12. Test at Low Volume First

For every new installation:

Power Check → Speaker Check → Input Check → Low-Volume Test → Tone Adjustment → Gradual Volume Increase

⚠️ Troubleshooting

Bluetooth Does Not Connect

Check:

• Amplifier power

• Bluetooth enabled on source

• Distance

• Previous paired device

• AUX/input condition

AUX Has No Sound

Check:

• AUX cable

• Source volume

• Bluetooth connection

• 3.5mm connector

• Speaker wiring

Disconnect Bluetooth if necessary when using AUX.

Sound Distorts at High Volume

Possible causes:

• Insufficient power-supply current

• Low supply voltage

• Excessive bass boost

• Amplifier clipping

• Speaker limitation

Bass Causes Clipping

Reduce:

• Bass control

• Master volume

and verify the DC supply has sufficient current capability.

One Speaker Does Not Work

Check:

• Speaker wiring

• Speaker itself

• Audio source

• Left/right channel connection

Swap speakers between channels during troubleshooting to isolate the fault.

Amplifier Gets Too Hot

Reduce output and check:

• Speaker impedance

• Power supply

• Ventilation

• Wiring

• Heat-sink clearance

Engineering Principle

Good stereo performance requires correct matching of:

Audio Source + Clean Power Supply + Amplifier + Speaker Impedance + Speaker Power + Wiring + Cooling

The advertised amplifier wattage is only one part of the complete audio system.

FAQ

1. What is the CA-502MT / ZK-502MT?

It is a compact 2.0-channel Bluetooth stereo audio amplifier board with independent volume, bass and treble controls.

2. What is the maximum output?

Maximum published output:

50W + 50W

under the appropriate supply and speaker conditions.

3. When can it produce 50W + 50W?

The published maximum condition is approximately:

24V DC + 4Ω Speakers

Actual output depends on the complete system.

4. How much power does it produce at 12V?

Published values are approximately:

12V / 8Ω → 12W + 12W

12V / 4Ω → 20W + 20W

5. How much power does it produce at 19V?

Approximately:

19V / 8Ω → 30W + 30W

19V / 4Ω → 40W + 40W

6. Is this a stereo amplifier?

Yes.

It provides:

• Left channel

• Right channel

7. Is this a 2.1-channel amplifier?

No.

The ZK-502MT is a 2.0-channel stereo amplifier and does not have a dedicated amplified subwoofer channel.

8. Does it have Bluetooth?

Yes.

It supports:

Bluetooth 5.0

9. What is the Bluetooth range?

Up to approximately:

15 metres in an open/unobstructed environment

Actual range can vary.

10. Does it have AUX input?

Yes.

It has a standard 3.5mm AUX audio input.

11. Does it support USB music playback?

USB music playback is not listed as a feature of the standard ZK-502MT.

12. Does it have bass control?

Yes.

Independent bass adjustment is provided.

13. Does it have treble control?

Yes.

Independent treble adjustment is provided.

14. What power supply does it require?

Supported range:

DC 9V–24V

A supply capable of at least approximately 3A is recommended, with greater capacity required for higher output.

15. Which power supply should I use for high output?

For high-power operation, RoboGears recommends approximately:

24V DC / 5A

16. Can I use a 12V adapter?

Yes.

12V is within the supported range, but maximum available output will be considerably lower than at 24V.

17. Can I use a 19V laptop adapter?

A suitable regulated 19V DC adapter can be used if:

• Polarity is correct

• Connector is compatible

• Current capacity is sufficient

At 19V, published output is approximately up to 40W + 40W with 4Ω speakers.

18. Can I use a 24V battery pack?

A nominal 24V battery pack is not recommended because its fully charged voltage may exceed the amplifier's 24V maximum input specification.

19. Which speakers can I use?

Published compatibility:

4Ω–8Ω

with approximately:

15W–100W speaker power

20. Does it have a dedicated subwoofer output?

No.

It is a two-channel stereo amplifier.

21. Does it have protection features?

Yes.

Published protection functions include:

• Overheat protection

• Overcurrent protection

• Short-circuit protection

22. What is the signal-to-noise ratio?

Published SNR:

>90dB

23. What are the dimensions?

Approximately:

89 × 60 × 21mm

with the protective shell.

24. Is a power supply included?

No.

A suitable DC power supply must be purchased separately.

25. Are speakers included?

No.

Passive speakers need to be purchased separately.

26. Is the acrylic protective shell included?

Yes, according to the current RoboGears package listing.

27. Which amplifier IC does the ZK-502MT use?

The exact amplifier IC should not be assumed from the model name.

Published ZK-502MT documentation identifies it as using a domestic amplifier-chip solution. The related ZK-502T is commonly documented with the TPA3116D2.

For accurate product information, verify the IC fitted to the actual ZK-502MT stock before advertising a specific chip model.

28. Is it suitable for DIY Bluetooth speakers?

Yes.

Its compact size, Bluetooth input, stereo output and built-in tone controls make it particularly suitable for DIY Bluetooth and desktop stereo speaker projects.

Important Safety Note

• Use DC power only.

• Observe correct polarity.

• Do not exceed 24V DC.

• Do not use an unregulated nominal 24V battery pack if its charged voltage can exceed the amplifier limit.

• Disconnect power before changing speaker connections.

• Prevent speaker-output short circuits.

• Use 4Ω–8Ω speakers.

• Provide ventilation around the amplifier.

Disclaimer

The 50W + 50W figure represents the published maximum output under suitable operating conditions and should not be interpreted as continuous output at every supply voltage or speaker impedance.

Actual output depends on power-supply voltage/current, speaker load, input signal, wiring and thermal conditions.

PCB colour, chip revision, shell appearance, knobs and other minor components may vary between manufacturing batches while maintaining the intended ZK-502MT functionality.