100 Watt Audio Amplifier Circuit using Transistors

This is 100 Watt Audio Amplifier Circuit using Transistors.

It makes weak audio signal strong for driving big speaker.

Transistors work as amplifier stage by giving more power.

With this circuit sound become loud and clear.

It can be used in music system, home theater or party speaker.

Circuit Working:

Parts List:

In this above circuit diagram first weak signal become strong using resistors, capacitors and transistors Q1, Q2.

Next the signal get more power in middle stage.

R8, R15 work with Q1.

R9, R10, R11, R12, R13 work with Q2.

Q4 and Q6 help in this step.

Last stage send strong signal to loudspeaker.

This stage uses Q5 and Q7.

Speaker is at low impedance and amplifier is at high impedance.

Driver stage matches this so speaker does not get damage.

Circuit can give up to 100 watts.

Power supply give (+) and (−) voltage and normal to 35V.

Formulas:

When making 100W audio amplifier with transistors we should think about:

• Transistor ratings
• Heat control
• Stable and good working circuit

Output Power:

Pout = Vpeak² / (2 × RL)

where,

• Vpeak is 35V − Vsat (loss in transistor)
• RL is speaker resistance

Power Loss (Heat):

Pdiss = VCE × IC

where,

• VCE is voltage between collector and emitter
• IC is collector current

This help us to know heat for choosing heatsink.

For safe and strong 100W amplifier use better parts and design.

How to Build:

To build a 100 Watt Audio Amplifier Circuit using Transistors follow the below mentioned connections steps:

• Connect Q1 collector to +35V with resistor R.
• Q1 base goes to audio input through capacitor C1.
• Q1 emitter join with Q2 emitter.

• Q2 collector connect to +35V.
• Q2 base goes to resistor R6.
• Q2 emitter connect to −35V through R3 and R4.

• Q3 base goes to one side of capacitor C5.
• Q3 collector go to Q4 base.
• Q3 emitter go to +35V.

• Q4 base connect to Q3 emitter.
• Q4 collector connect to +35V.
• Q4 emitter goes to Q5 base.

• Q5 base connect to Q4 emitter.
• Q5 collector connect to +35V.
• Q5 emitter goes to loudspeaker through R16.

• Q6 base goes to R10 and R11.
• Q6 collector goes to Q7 base.
• Q6 emitter goes to resistor R15.

• Q7 base connects to Q6 collector.
• Q7 collector connects to loudspeaker.
• Q7 emitter connects to −35V through R14.

• R5 and C3 from Q2 base go to ground.
• C2 positive between R3 and R4 and negative go to ground capacitor C3.
• R8 from +35V through diodes D1, D2 go to point between R9 and R10.

Safety:

• Use good solder tools.
• Transistors make much heat so we should use heatsink and thermal paste.
• Test first at low volume and then watch for problems.
• Check wires and parts before power ON to avoid short or burn.

Conclusion:

100 Watt Audio Amplifier Circuit using Transistors make weak audio become loud using 3 stages:

Pre-amp (voltage gain), Driver stage, Power output stage

It uses dual polarity power with +35V and −35V and gets hot.

So always follow safety rules while building and testing.

References:

Datasheet BC108

Datasheet 2N6107

Datasheet 2N5294

Datasheet 2N3773