Here the circuit diagram of 25 watt high fidelity audio amplifier that build based on single Power Amplifier IC LM1875.

Component part list

R1 _____________ 1K
R2 _____________ 1M
R3 _____________ 22K
R4 _____________ 10K
R5 _____________ 180K
R6 _____________ 1R

IC1 ____________ LM1875

C1 _____________ 1uF 50V
C2,6 ___________ 100nF
C3 _____________ 22uF 63V
C4 _____________ 0.22uF
C7,5 ___________ 220uF 50V     

Miscellaneous:
Fuse holder & cover
2 amp fuses

Circuit Desc:
The IC can be used with two power supply arrangements single supply and dual supply. We have decided to use the dual supply version. The single supply version would require the use of 63V electrolytic capacitors, thus increasing the cost and overall size of the module.

Here the low resistance connection tester which can be used as cable or wire tester, soldered joints and other types of connection with resistance value between 0.25 and 4 ohm.

Notes
This simple circuit uses a 741 op-amp in differential mode as a continuity tester.

This is a 18W audio amplifier circuit based on power IC HA13118. The supply voltage required for this circuit is 8 – 18V DC, at least 1 to 2 Amps. Maximum output power will only be obtained with a power supply of 18V at greater than 2 A, using a 4 ohm speaker. The power supply should be well filtered to reduce mains hum, a regulated supply will reduce noise even further. Extra filtering is unnecessary if operating from a battery supply.

Components

Resistors :
R1, R2___________________ 2R2 ohm

Capacitors :
C1, C2, C4, C5, C6_______ 100uF/16V electrolytic capacitor
C3_______________________ 10uF/16V electrolytic capacitor
C7, C8, C12______________ 100nF
C9_______________________ 2,200uF/25V electrolytic capacitor
C10______________________ 1uF/50V electrolytic capacitor
C11______________________ 100pF

Misc.
I.C._____________________ HA13118
Heatsink