In the following video, I am showing how you can make a powerful DIY homemade D718 amplifier using four D718 NPN transistors. This is a class-A amplifier with low efficiency. I am just demonstrating it for educational purpose. Its design is with minimum components for beginners or students. We do not recommend it for continuous professional use without modification or addition of pre-amp. I used 12 volts pc power supply of 5 amperes to run this project. I recommended 4 ohms speakers of any size. Two speakers of 4 to 8 ohms can be joined together in parallel. If you are using more than 4 ohms then use two of them together in with parallel connection which will reduce its resistance in half.
Following image shows the circuit diagram for above video of quad D718 NPN transistors class-A amplifier. The circuit used only one resister of 1k, one electrolytic capacitor of 1000uf, one 100k single potentiometer and a hand made coil of 150 to 200 turns from 26 awg copper enameled wire.
of DIY homemade D718 amplifier
Stick four pieces of D718 transistors onto the heat sink with or without insulation. Connect all collectors with collectors, Base with base and emitters with emitters in parallel with piece of wires. Collector to collector joining is not necessary, if you stuck them on heat sink without insulation (mica). Because the center pin (collector) is already attached with the heat sink. Choose a large enough and thick heat sink for proper heat dissipation of transistors.
Now connect 1k resister from base to collector of any transistor because they are all connected each other in parallel. If you are not using the same method as in the below image then be sure the wires are fully insulated to prevent short circuits.
Take one 1000uf electrolytic capacitor and solder its positive end with base pin.1 of any transistor. The negative end of capacitor solder to center pin of volume controller. Connect pin.3 of volume controller to ground pin.3 emitter of the transistor.
Wind 26 AWG enameled wire on 1″ large tube 150 to 200 turns. Solder one end to the collector pin.2 of D718 transistor.
The other end of coil will go to the speakers black terminal.. The negative point of power supply socket will go ground i.e. pin.3 emitter of the transistor. The positive +12v from the power supply socket will be connected to the red terminal of the speaker.
Take out a wire from first pin of volume controller and connect to 3.5mm audio jack left & right channel wires. And the ground wire of audio jack will go to ground i.e. pin.3 emitter of transistor.
Now insert the audio jack into mobile or any audio source. Play music and enjoy the project.
List of components
used in DIY homemade D718 amplifier
- D718 transistor x 4
- 1000uf capacitor (10 to 22uf recommended) x 1
- 100k pot x 1
- Coil 26 AWG/150 turns x 1
- Power supply 12 volts
- Speaker 4 ohms
- Power socket 12v x 1 (optional)
- Speaker male/female connectors (optional)
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