Simple 3 Channels Mini Audio Mixer

This is the simple and low cost 3 channels mini audio mixer circuit diagram. This circuit supplied using 9V power supply. There are high/low-sensitivity switchable inputs for each input channel and each channel used low noise and high gain transistor of BC550C.

35W Power Audio Amplifier based LM391

Here the 35W power audio amplifier circuit based on LM391. Inductor L1 is constituted by 20 coils of wire, with thickness 0.9mm, round resistor R16. The transistors Q3-4 are the final amplification section, it should be placed on heatsink. If are used the Q3-4 in packing TIPxxxx they can be placed straight above in PCB.… Read More »

18W Audio Amplifier

This is the circuit diagram of 18W audio amplifier. The circuit is quite simple and inexpensive to built. It uses a pair of power transistor TIP41A and TIP42A for single channel operation. The power supply used for this circuit is dual polarity (splitted) power supply, use center tap transformer to build this kind of power… Read More »

Diode Zener Tester

This is the circuit diagram of zener diode tester which tests zener diodes with breakdown voltages extending up to 120 volts. This is a handy circuit and will help you to measure the zener diode easily. This diode zener tester can be fitted in a 9V battery box. 1/3 of the box may be used… Read More »

Active FM Booster

This is a simple low cost circuit of an active FM booster that can be used to amplify the FM band signal, so you can listen the FM channels/programs from distant FM stations clearly. The circuit make use of a common-emitter tuned RF preamplifier wired around VHF/UHF transistor 2SC2570. (Only C2570 is annotated on the… Read More »

Digital Variable Resistor / Potensiometer DS1669

The DS1669 is an electronic digital rheostat manufactured by Dallas Semiconductor. This component has a function similar to digital variable resistor/potensiometer which can be operated by push the buttons. You can adjust the audio volume, LCD contrast, frequency, etc. by using two buttons instead of a common potentiometer/trimpot. This circuit explains how we do it… Read More »

2 Way Speaker Box Design

This is 2 way speaker box design for audio system. I’ve used this design for my home audio system, the sound quality is good. Two speakers used for this speaker box that are tweeter / high frequency speaker and woofer / low frequency speaker / subwoofer. Alternatively you may replace the woofer with fullrange loudspeaker.

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