Calling all music lovers who want their speakers to sound REALLY loud!
This article shows how to build a super powerful amplifier circuit that can pump out 300 watts of sound with 8 ohm speakers or even more with 4 ohm speakers.
Building circuits with high voltage can be dangerous.
If possible experiment this circuit under adult supervision and a qualified electrician should install at home.
This project is not recommended for beginners.
What is a 300 Watt Power Amplifier Circuit:
With a power output of around 300 watts, a 300 watt power amplifier circuit is an electrical circuit used to amplify audio signals.
Such a circuits function is to boost the intensity of a low power audio signal such that it can power speakers sufficiently to provide clear and loud music.
Circuit Working:
Parts List:
| Component | Quantity |
|---|---|
| Resistors (All resistors are 1/4 watt) | |
| 12k,1k, 47k, 2.7k, 3.9k, 33k, 2.2k, 47Ω, 85Ω, 270Ω 1W, 390Ω, 100Ω | 1 each |
| 680Ω, 270Ω,120Ω 1/2W, 10Ω 5W | 2 each |
| 47Ω 5W | 4 |
| Capacitors | |
| PPC 220nF, 47nF, 100nF | 1 each |
| PPC 100pF, 56pF | 2 each |
| Electrolytic 100uF 50V, 47uF 25V, 47uF 40V, 470uF 40V | 1 each |
| Semiconductors | |
| Diodes A,B,C 1N4007 | 3 |
| Diodes 1N4001 | 1 |
| Transistors BC556, BD139, TIP140, TIP145 | 2 each |
| Transistor BD140 | 1 |
| Speaker 4Ω | 1 |
To achieve the required high power output while protecting Hi-Fi audio quality this designed amplifier circuit makes use of complementary transistors.
The device draws no more than 7 amps of electricity and is powered by a 45V + 45V source.
The majority of integrated transistors with a couple of the BC556 should be connected to a heatsink usually placed on one side of the cabinet to provide proper heat dissipation.
It is also necessary to use thermal grease to connect the diodes A, B and C 1N4007 to the heatsink.
The music that is sent into the amplifier should follow the 1Vpp standard line for best results.
Formula:
While building a power amplifier using NPN and PNP transistors one should follow the following simple formulas:
Bias:
Voltage divider bias is a common biasing method for both NPN and PNP transistors.
The following formula are used to find the resistor values R1 and R2 are:
R1 = (Vcc – Vbe) / Ib
R2 = (R1 * β) + Re (for NPN)
R2 = (R1 * β) – Re (for PNP)
where,
- Vcc is the supply voltage
- Vbe is the base emitter voltage which is around 0.7V for silicon transistors
- Ib is the base current for desired biasing current
- β is the current gain of the transistor hFE
- Re is the emitter resistor used for stability which is an optional
Power Loss:
Transistor Power Dissipation:
One should monitor a transistors while they are overheating.
The below mentioned following formula are used to calculate the transistors power dissipated (Pd):
Pd = (Vce * Ic) + (Vbe * Ib)
where:
- Vce is the collector emitter voltage
- Ic is the collector current
Transformer Turns Ratio: Transformer Coupled Design:
The transformers turns ratio (Np/Ns) controls the impedance matching between the speaker and the amplifier output.
One can calculate it by using the formula below:
Np / Ns = √(RL / Rp)
where:
- Np is the number of turns in the primary coil which is connected to the amplifier
- Ns is the number of turns in the secondary coil which is connected to the speaker
- RL is the speaker impedance
- Rp is the desired primary impedance which is usually chosen based on transistor characteristics
Important Details:
For a complete amplifier design one needs to perform deeper calculations and consider more variables but these are only a few basic formulas.
See the amplifier schematics and design guides to choose the right components and do detailed calculations depending on the desired output power and other factors.
How to Build:
To build a Simple 300 Watt Power Amplifier Circuit using Transistors following steps are required for connections:
A diagram Design:
- The 300 watt power amplifier circuits schematic diagram should be collected or designed first.
- Transistors, resistors, capacitors and other parts should be arranged as part of this.
PCB Design:
- Using the schematic design as a guide create a PCB design.
- Using the schematic as a guide arrange the components on the PCB ensuring there is enough space for proper heat dissipation and with minimal noise.
Mounting Transistors:
- On the PCB mount the corresponding transistors.
- Be sure the transistors have been placed correctly and that the correct transistors are used.
- As shown by the circuit diagram above connect them.
Heatsink Connector:
- Connect the heatsink to the PCBs desired location.
- All transistors except BC556 and diodes A, B and C 1N4007 should be mounted on the heatsink.
- To enhance the transfer of heat use thermal grease.
Positioning of Components:
- As shown in the diagram install resistors, capacitors, inductors and diodes on the PCB.
- Take note of their polarity and values.
Connecting:
- Connect the wires to the components by following the PCBs traces.
- For high current routes use the right wire gauges.
Connection to the Power Supply:
- Connect the power supply to the circuit for the amplifier.
- Check that the supply voltage falls between 45V and 45V as required.
- Take care to prevent short circuits.
- Before shutting the cabinet use a normal line music input of 1Vpp to test the amplifier.
- Use a multimeter or oscilloscope to check the output.
- Make changes as required.
The enclosure:
- After the circuit has been confirmed to function properly put it within an enclosure.
- Be sure there is enough airflow to dissipate heat.
Last Testing:
- Use the included amplifier to do last minute testing.
- Check for circuit performance which should stay on track and satisfies the requirements.
Conclusion:
The construction and operation of high power amplifier circuits requires knowledge of electronics and by following to safety standards.
The possible dangers of handling high voltages and currents should be understood by users.