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| Simple 50W RMS Audio Amplifier with Mosfet |
Hello, electronics enthusiasts!
Today we're going to dive into the fascinating world of audio amplifiers! Get ready to build a simple yet excellent quality Audio Amplifier with 2 Mosfet output transistors that will surprise you with its 50W RMS on an 8 ohm speaker.
This project is perfect both for beginners who want to improve their skills and for hobbyists looking for an efficient amplifier with good sound quality.
🔬 Amplifier Technical Specifications
| Output Power | 50W RMS |
| Load Impedance | 8 ohms |
| Supply Voltage | +/- 35V DC |
| Maximum Current | 2A (mono) / 4A (stereo) |
| Output Configuration | Complementary push-pull with Mosfets |
👨🔧 How Does This 50W RMS Amplifier Work?
Before we get our hands dirty, let's understand how this circuit works. The amplifier is divided into three main stages, each with a specific function to ensure clear and powerful sound reproduction.
1️⃣ Input Stage: Differential Amplifier
The first stage of the amplifier is a differential amplifier based on the PNP transistors BC556, Q1 and Q2. This stage is responsible for receiving the low-amplitude audio signal and preparing it for the following stages.
The capacitor C2 functions as an input DC decoupler, ensuring that only the audio signal passes through. The resistor R1 limits the input current, protecting the circuit, and the capacitor C1 diverts unwanted high frequencies, functioning as a simple low-pass filter.
2️⃣ Driver Stage: The Heart of the Amplifier
The second stage is the drive stage composed of the transistors Q3, BC546, and the transistor Q4. This section functions as a voltage amplifier, increasing the signal received from the input stage and preparing it for the output stage. Additionally, this stage aims to regulate the bias of the output transistors, ensuring they operate in their linear region and minimizing distortion.
3️⃣ Output Stage: Power and Efficiency with Mosfets
The output stage is a complementary push-pull stage based on the MOSFETs IRF530 and IRF9530. This configuration is ideal for power amplifiers, as one MOSFET conducts the positive half of the signal while the other conducts the negative half, resulting in high efficiency and low distortion.
The output is coupled to the speaker using the inductor L1, which helps to isolate the speaker from any DC component that might be present in the output signal.
💡 Expert Tip
If you don't have access to any of these specific transistors, don't worry! We provide on our website a tool called:
Equivalent BJT Transistor by Data Cross-Reference
With this tool, you ensure the correct functioning of the circuit, even using components different from those suggested here.
📌 Additional Components: Stability and Quality
The network composed of R15 and C5 is intended for noise reduction, functioning as a Zobel filter to stabilize the load and prevent high-frequency oscillations. The capacitors C6 and C7 are power supply filters, essential for eliminating ripple and ensuring a clean power supply for the circuit.
The variable resistor R6 is a crucial component intended to adjust the quiescent current of the bias transistor, allowing optimization of the MOSFETs' operating point for lower distortion.
🔌 50 Watt Amplifier Circuit Diagram
In Figure 2 below, we have the schematic diagram of the circuit. Despite being a circuit with few components, we must pay special attention during assembly, as we are working with at least 6 transistors, diodes, and electrolytic capacitors with defined polarities.
⚠️ Attention: If any component is inverted, we can cause component burnout or even small explosions, in the case of capacitors. Always check the polarity before soldering!
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| Fig 2 - Schematic Diagram 50W RMS Audio Amplifier with Mosfet |
💡 Tips for Circuit Assembly
We don't currently have a printed circuit board, so when building your amplifier, assemble it on a good quality PCB. Here are some important tips:
- Use a good quality printed circuit board with thick copper to support the necessary current
- Keep audio signal traces as short as possible to reduce noise
- Separate power traces from signal traces to avoid interference
- Use good quality solder and check all connections before powering the circuit
You might also be interested in:
- 160W High Fidelity Amplifier using Mosfet 2SK1058 and 2SJ162 with PCB
- 440W Class AB Power Amplifier using Mosfet IRFP9240 and IRFP240 with PCB
- 200W RMS Power Amplifier With 2SC2500 AND 2SA1943 + PCB
- 300W RMS Power Amplifier - 2SC3858 and 2SA1494 Transistors + PCB
- 50W RMS Audio Amplifier with IRF530 and IRF9530 Mosfet + PCB
- 100W RMS Power Amplifier With 2 NPN 2SC5200 Transistors At Output + PCB
- Simple 3 Transistors Power Amplifier push a 600W RMS Subwoofer + PCB
🧾 Complete Bill of Materials
To facilitate your assembly, we've organized all necessary components in a clear and detailed table. Note everything before starting your project!
⚡ Adequate Power Supply
To ensure maximum performance of your amplifier, it's crucial to use an adequate power supply. The required power supply is of the symmetric type +/- 35V DC, with a current of at least 2 Amperes.
This voltage and current are essential for the amplifier to deliver the promised 50W RMS with low distortion.
💡 Tip for Stereo Configuration
For those who want to build a stereo amplifier, just build two identical circuits and double the power supply current to 4 Amperes. Remember that each channel will need its own set of components and heat sink!
🌀 Construction of Coil L1
For the coil L1, wind 12 turns of enameled copper wire 18AWG with a diameter of 3/8" or 1cm without a physical core. This coil is crucial to isolate the speaker from any DC component and improve the frequency response of the amplifier.
🔵 Selection of Capacitors
The electrolytic capacitors C6 and C7, which act as power supply filters, should have minimum voltages of 50V to ensure safety and durability. The other electrolytics can be 25 or 35V, as long as they respect the specified capacitance values.
📏 Essential Heat Sink
An adequate Heat Sink is necessary for the MOSFETs. We recommend a heatsink with medium dimensions of 22x12x12cm with sufficient dissipation area to ensure that the transistors operate at safe temperatures, even at higher volumes. Remember to use thermal paste between the MOSFETs and the heatsink for better heat transfer!
⚠️ Important Warning
Pay attention to the speaker, as the output of this amplifier is 50W RMS. Make sure your speaker can handle this power to avoid damage. Speakers with lower power can be damaged at higher volumes!
🎵 Test and Adjustment
After assembling the circuit, before connecting the speaker, adjust the trimpot RP1 to approximately the middle of its course. Connect a multimeter in series with the power supply and check if the quiescent current is between 50-100mA. Adjust RP1 as necessary to obtain this value.
🤔 Possible Problems and Solutions
If you encounter problems during the assembly or operation of the amplifier, here are some solutions to the most common problems:
| Problem | Possible Cause | Solution |
|---|---|---|
| No sound at output | Incorrect connections or damaged components | Check all connections and test the components |
| Distorted sound | Incorrect bias or insufficient power supply | Adjust RP1 and check the power supply |
| MOSFETs overheating | Inadequate heatsink or excessive bias | Improve the heatsink or reduce the RP1 adjustment |
| High-frequency noise | Instability or interference | Check capacitor C5 and the board layout |
🛠️ Optional Improvements
If you want to take your amplifier to the next level, here are some improvements that can be implemented:
- Short-circuit protection: Adding a protection circuit can prevent damage to the MOSFETs in case of a short at the output.
- Enhanced power supply filter: Larger capacitors or addition of inductors in the power supply can further reduce noise.
- Mute circuit: Implementing a mute circuit can prevent noise when turning the amplifier on/off.
- Power indicator: Adding LEDs or a VU meter can give a more professional look to your project.
❓ Frequently Asked Questions (FAQ)
1° What is the real power of this amplifier?
This amplifier delivers 50W RMS on an 8-ohm speaker, when powered with a symmetric supply of +/- 35V. This is real power (RMS), not peak power or PMPO.
2° Can I use other MOSFET transistors instead of IRF530 and IRF9530?",
Yes, you can use other MOSFETs with similar characteristics. We recommend MOSFETs with operating voltage of at least 60V and maximum current of 17A or more. Some possible substitutes are IRF540/IRF9540 or IRFZ44/IRF9Z34.
3° Does this amplifier need a symmetric power supply?
Yes, this circuit was designed to work with a symmetric power supply of +/- 35V. Trying to use a single supply will result in incorrect operation and possibly damage to the components.
4° How should I adjust the trimpot RP1?
The trimpot RP1 adjusts the quiescent current (bias) of the MOSFETs. Start with it in the central position and measure the quiescent current with a multimeter. The ideal is between 50-100mA. Adjust slowly until you obtain this value. A very low current can cause distortion, while a very high one can overheat the transistors.
5° Can I use this amplifier for subwoofers?
Yes, this amplifier works well for subwoofers, but you may need to adjust the value of capacitor C1 to decrease the cutoff frequency of the input high-pass filter. A value between 470pF and 1nF would be more suitable for subwoofer applications.
Good luck with your project!
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Original article published on FVML (Portuguese) – August 12, 2019
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