Here is the very simple, inexpensive and useful project telephone amplifier using very common power amplifier LM386 and some more components. It is used to produce loud sound in order to talk in group.

Working of the circuit telephone amplifier

The output telephone signal is more powerful then the signal fed to base of the transistor T₁. The output signal from transistor T₁ is fed to pin no 3 of power amplifier LM386 which amplify up to necessity level and output is obtained from pin no 5 is fed to speaker through capacitor C₉. The V_CC is given to IC₁ through pin 6. The telephone signal is fed in to circuit through two ways.

1. Direct supply telephone signal from telephone line to the point where coil L₁ is connected as shown in figure 2.
2. Or connect this peak up coil L₁ and so adjusted near telephone set where excellent voice be able to single out. 

PARTS LIST

Resistors (all ¼-watt, ± 5% Carbon)

R₁ = 100 KΩ

R₂ = 39 KΩ

R₃ = 2.2 KΩ

R₄ = 680 Ω

R₅ = 100 Ω

VR₁ = 4.7 KΩ

VR₂ = 10 KΩ

Capacitors

C₁ = 27 KPF (273)

C₂, C₄ = 2.2 µF/16 V

C₃ = 22 µF/16 V

C₅, C₁₀ = 100 µF/16 V

C₆ = 10 µF/16 V

C₇ = 100 KPF (104)

C₈ = 47 KPF (473)

C₉ = 220 µF/16 V

Semiconductors

T₁ = BC147B

IC₁ = LM386 power amplifier

Miscellaneous

L₁ = Pick up Coil

Speaker 8Ω

SW₁ = On/Off switch