LM324E SMD Bass Treble Preamplifier Board – Dual-Channel 12V-24V DC Audio Tone Control Module with Integrated Volume, Bass, and Treble Adjustments

Key Features

• LM324 quad operational amplifier

• Active stereo tone-control circuit

• 2.0-channel audio processing

• Integrated master volume control

• Dedicated bass adjustment

• Dedicated treble adjustment

• DC 12V–24V operating range

• Stereo line-level audio input

• Stereo line-level audio output

• Published 20Hz–20kHz frequency response

• SMD component construction

• Compact board profile

• Suitable for external power amplifiers

• Suitable for DIY home-audio systems

• Suitable for Bluetooth audio projects

• Suitable for amplifier upgrades

Technical Specifications

Control Functions

The board provides three primary controls:

Volume

Controls the overall stereo signal level sent to the downstream power amplifier.

Bass

Adjusts the low-frequency content of the audio signal.

Treble

Adjusts the high-frequency content of the audio signal.

Together, these controls allow basic adjustment of the overall sound character before power amplification.

Active Tone Control

Unlike a simple passive tone network, this board uses an operational-amplifier-based active circuit.

This allows the circuit to actively process the audio signal while providing adjustable bass and treble response.

LM324 Operational Amplifier

The LM324 is a quad operational amplifier containing four amplifier channels in one IC.

In this board it forms part of the active stereo preamplifier/tone-control circuitry.

Important Power Rating Note

The 12V–24V rating refers to the operating supply of this preamplifier board.

It does not represent speaker output voltage or amplifier power.

The LM324E board should feed a separate audio power amplifier.

Compatibility

The LM324E board is designed to process a stereo line-level audio signal before it reaches a power amplifier.

Compatible Audio Sources

It can be used with compatible line-level sources such as:

• Bluetooth audio receiver modules

• USB / MP3 decoder modules

• AUX audio sources

• Phones with compatible analogue audio output

• Computers

• Music players

• Other line-level stereo sources

Compatible Power Amplifiers

The processed output can feed compatible analogue-input amplifier boards such as:

• PAM8403

• TPA3110

• TPA3116D2

• TPA3118

• TPA3255

• Other compatible stereo power amplifiers

Always verify the input-level and grounding requirements of the amplifier being used.

Example — Bluetooth Amplifier

Smartphone

↓

Bluetooth Receiver

↓

LM324E Tone Control

↓

Stereo Power Amplifier

↓

Left + Right Speakers

This arrangement provides:

Bluetooth + Volume + Bass + Treble + Speaker Amplification

Example — MP3 Decoder System

USB / TF / Bluetooth MP3 Decoder

↓

LM324E Preamplifier

↓

Power Amplifier

↓

Speakers

The decoder provides the audio source, the LM324E provides tone adjustment, and the power amplifier drives the speakers.

Power Compatibility

The LM324E board requires:

DC 12V–24V

Do not exceed the specified board supply range.

When sharing a supply with an amplifier, verify that:

• Both boards support the same voltage

• Supply capacity is sufficient

• Grounding is correct

• Power-supply noise is acceptable

Important — Not a Speaker Amplifier

Do not use:

Audio Source → LM324E → Passive Speakers

Instead use:

Audio Source → LM324E → Power Amplifier → Passive Speakers

Before Purchase

IC: LM324

Channels: Stereo / 2.0

Supply: 12V–24V DC

Volume Control: Yes

Bass Control: Yes

Treble Control: Yes

Input: Line-Level

Output: Line-Level

Direct Speaker Drive: No

External Power Amplifier Required: Yes

Applications

• DIY stereo amplifiers

• Bluetooth speaker systems

• Home audio projects

• Custom amplifier builds

• Audio tone-control projects

• Multimedia speaker systems

• Existing amplifier upgrades

• Car-audio experiments

• Desktop audio systems

• Electronics prototyping

• Student audio projects

• Repair and modification projects

Who Is It For?

• DIY audio builders

• Electronics hobbyists

• Amplifier builders

• Engineering students

• Makers

• Audio repair technicians

• Custom speaker builders

📦 What's Included

❌ What's Not Included

The standard package includes only the preamplifier board.

The following components are not specified as included:

• Audio Power Amplifier

• Speakers

• Bluetooth Receiver

• MP3 Decoder

• Audio Cables

• DC Power Supply

• Power Adapter

• Enclosure

• External Wiring

Important Purchase Note

This product is a:

Stereo Preamplifier / Tone Control Board

It is not a complete audio amplifier system.

For a typical DIY system:

Audio Source

LM324E Tone Control

Power Amplifier

Speakers

Suitable Power Supply

are required.

Controls Included on the Board

The board itself provides three integrated potentiometers for:

• Volume

• Bass

• Treble

📚 Resources

The board uses an LM324-family quad operational amplifier.

For the operational amplifier itself, the LM324 manufacturer datasheet can be used to understand the basic electrical characteristics of the IC.

However, the LM324 datasheet is not a wiring diagram for this complete tone-control board.

Always follow the input, output and power markings printed on the actual PCB supplied.

Getting Started

Step 1 — Identify the PCB Connections

Before applying power, inspect the board and identify:

• DC Positive

• Ground

• Left Audio Input

• Right Audio Input

• Input Ground

• Left Audio Output

• Right Audio Output

• Output Ground

Follow the actual PCB markings.

Step 2 — Select the Power Supply

The board requires:

DC 12V–24V

Use a clean regulated DC supply.

Step 3 — Connect the Audio Source

Connect a compatible stereo line-level source to the board's audio input.

Possible sources include:

• Bluetooth receiver

• MP3 decoder

• AUX source

• Computer

• Compatible music player

Step 4 — Connect the Output to an Amplifier

Connect the preamplifier output to the line-level input of a compatible stereo power amplifier.

The basic architecture is:

Audio Source → LM324E → Power Amplifier

Step 5 — Connect the Speakers to the Power Amplifier

The speakers connect to the:

Power Amplifier

not directly to the LM324E preamplifier.

Step 6 — Set the Controls

Before initial power-up, place:

• Volume at a low setting

• Bass near the centre

• Treble near the centre

This provides a safer starting point for testing.

Step 7 — Apply Power

Apply a suitable:

12V–24V DC

supply.

Step 8 — Start Audio Playback

Play audio from the connected source.

Step 9 — Increase Volume Gradually

Slowly increase the volume until the required listening level is reached.

Step 10 — Adjust Bass and Treble

Adjust the tone controls according to the desired sound.

Avoid excessive boost if the downstream amplifier or speakers begin to distort.

Basic Bluetooth Amplifier Setup

Phone

↓

Bluetooth Receiver

↓

LM324E Bass/Treble Preamplifier

↓

Power Amplifier

↓

Speakers

Important

Never assume connector positions from another visually similar preamplifier board.

Follow the markings on the actual RoboGears-supplied PCB.

🔧 Prototyping and Engineering Tips from RoboGears

1. Install the Preamplifier Before the Power Amplifier

Correct signal chain:

Source → Preamplifier → Power Amplifier → Speakers

The LM324E performs signal processing and tone adjustment.

The power amplifier provides the current and power required by the speakers.

2. Do Not Connect Passive Speakers Directly

The LM324E output is line-level.

It is not intended to drive 4Ω or 8Ω passive speakers directly.

3. Use a Clean DC Supply

Poor-quality power supplies can introduce:

• Hum

• Buzz

• Ripple

• Switching noise

A clean regulated 12V–24V DC supply is preferable.

4. Keep Signal Wiring Short

Long unshielded audio cables can pick up:

• Mains hum

• RF interference

• Switching noise

• Transformer noise

Keep input and output signal wiring short where practical.

5. Use Shielded Audio Cable

Shielded cable is particularly useful between:

Audio Source → LM324E

and:

LM324E → Power Amplifier

when wiring distances are significant.

6. Keep Signal Wiring Away From High-Current Wiring

Do not route low-level audio signals directly alongside:

• Speaker output wires

• SMPS switching sections

• Motor wiring

• Transformer wiring

• High-current DC cables

Physical separation can reduce noise pickup.

7. Start With Tone Controls Near Centre

During initial testing:

Bass → Centre

Treble → Centre

Volume → Low

Then adjust gradually.

This makes troubleshooting easier.

8. Excessive Bass Boost Can Cause Clipping

Boosting bass increases the signal level in the low-frequency region.

If the audio source, preamplifier or downstream power amplifier runs out of headroom, distortion can occur.

If the sound becomes distorted:

• Reduce bass boost

• Reduce source level

• Reduce preamp output level

• Check the power amplifier

9. Match the Supply to the Whole System

If the LM324E and power amplifier share one supply, make sure the selected voltage is acceptable for both boards.

For example, if both boards support 12V operation, a properly sized 12V supply may simplify the system.

10. Watch for Ground Loops

Incorrect grounding can create audible hum.

Keep the audio signal ground arrangement clean and avoid unnecessary ground paths.

11. Power Filtering Can Help With Hum

If the DC supply contains ripple, additional filtering near the preamplifier may help.

The current RoboGears page suggests a 1000µF capacitor across the power input as one possible troubleshooting measure for supply-related hum.

This is a troubleshooting suggestion rather than a universal requirement.

Observe correct capacitor polarity and use an appropriate voltage rating.

12. Do Not Describe the LM324 as a Power Amplifier IC

The LM324 is an operational amplifier.

Its role here is low-level audio signal processing.

The downstream power amplifier performs speaker amplification.

Common Mistakes / Troubleshooting

No Sound

Check:

• Power supply

• Input wiring

• Output wiring

• Source volume

• Preamp volume

• Power amplifier

• Speaker connections

Very Low Volume

Check:

• Input signal level

• Volume potentiometer

• Power-amplifier gain

• Audio grounding

Hum or Buzz

Check:

• Power-supply ripple

• Ground loops

• Signal cable routing

• Unshielded wiring

• Nearby transformer or SMPS

Distortion

Try:

• Reducing source volume

• Reducing bass boost

• Reducing treble boost

• Reducing preamp volume

• Checking amplifier headroom

One Channel Not Working

Check:

• Left/right input wiring

• Left/right output wiring

• Solder joints

• Audio source

• Power amplifier channel

Tone Controls Do Not Seem Effective

Verify that:

• Audio is entering the correct input

• Output is taken from the correct output

• The board is properly powered

• Potentiometers are functioning

• Signal grounds are correctly connected

Engineering Principle

A complete audio system can be divided into:

Source → Signal Processing → Power Amplification → Speakers

The LM324E belongs in the:

Signal Processing

stage.

FAQ

1. What is the LM324E board?

It is a stereo audio preamplifier and active tone-control board providing volume, bass and treble adjustment.

2. Which IC does it use?

The current RoboGears specification identifies an:

LM324 Quad Operational Amplifier

3. What is the operating voltage?

DC 12V–24V

4. Can I use a 12V supply?

Yes.

12V is within the specified operating range.

5. Can I use a 24V supply?

Yes.

24V is the upper end of the board's published operating range.

6. Can I use 5V?

The RoboGears board is specified for 12V–24V DC, so 5V operation should not be assumed.

7. Can I use 36V?

No.

36V exceeds the specified board operating range.

8. Is this a stereo board?

Yes.

It is specified as a 2.0-channel stereo preamplifier.

9. Does it control volume?

Yes.

10. Does it control bass?

Yes.

11. Does it control treble?

Yes.

12. How many potentiometers are provided?

Three:

• Volume

• Bass

• Treble

13. Is it a power amplifier?

No.

It is a preamplifier/tone-control module.

14. Can I connect speakers directly?

No.

Normal passive speakers require an external audio power amplifier.

15. What is the correct connection order?

Audio Source → LM324E → Power Amplifier → Speakers

16. Can I connect a Bluetooth receiver to it?

Yes.

A compatible Bluetooth receiver with line-level audio output can feed the LM324E input.

17. Can I connect an MP3 decoder?

Yes, provided the decoder provides a compatible line-level audio output.

18. Can I use it with TPA3116D2?

Yes, as a tone-control/preamplifier stage before a compatible TPA3116D2 amplifier.

19. Can I use it with TPA3255?

Yes, as a line-level tone-control stage before a compatible TPA3255 amplifier.

20. Can I use it with PAM8403?

It can be used ahead of a compatible PAM8403 amplifier, provided the power and signal-level requirements of both boards are handled correctly.

21. What is the published frequency response?

The current RoboGears listing states:

20Hz–20kHz

22. Does it increase bass?

The bass control allows adjustment of the low-frequency portion of the audio signal.

Excessive boost should be avoided if it causes clipping or speaker distortion.

23. Does it increase treble?

The treble control adjusts the high-frequency portion of the audio signal.

24. Can I use it in a DIY Bluetooth speaker?

Yes.

A typical system is:

Phone → Bluetooth Receiver → LM324E → Power Amplifier → Speakers

25. Can I use it in a home amplifier?

Yes.

It is suitable as a stereo tone-control stage in compatible DIY home-audio systems.

26. Can I use it in a car-audio project?

The board's 12V operating capability makes it potentially suitable for appropriately designed automotive audio projects.

Automotive electrical systems can experience voltage transients, so proper power regulation/protection is recommended for permanent installations.

27. Why do I hear hum?

Possible causes include:

• Noisy power supply

• AC ripple

• Ground loop

• Long signal wiring

• Poor shielding

• Transformer or SMPS interference

28. Can a capacitor reduce hum?

If the hum originates from power-supply ripple, additional supply filtering may help.

The current RoboGears page suggests a 1000µF capacitor across the power input as one possible troubleshooting step.

29. Why does the sound distort when I increase bass?

Heavy bass boost can increase signal amplitude and reduce available headroom.

Reduce bass, volume or source level and check the downstream amplifier.

30. Does it have Bluetooth built in?

No Bluetooth function is specified.

Use an external Bluetooth receiver if wireless audio is required.

31. Does it have USB playback?

No USB playback function is specified.

32. Does it have FM radio?

No FM tuner is specified.

33. Does it have a speaker amplifier?

No.

A separate power amplifier is required.

34. What is included?

1 × LM324E SMD Bass Treble Preamplifier Board

35. Is a power supply included?

No power supply is specified as included.

36. Are speakers included?

No.

37. Is a power amplifier included?

No.

Important Note

The LM324E board is a stereo preamplifier and tone-control module, not a speaker power amplifier.

Use it between a compatible line-level audio source and an external power amplifier.

Disclaimer

Actual audio performance depends on the power supply, source level, amplifier input characteristics, grounding, wiring and overall system design.

Do not exceed the board's specified 12V–24V DC operating range.