This kit is for OTL power amplifiers, using high-quality FR-4 military-grade A-grade board material, ensuring a high soldering success rate. This circuit is a classic example of analog electronics, and building it is both educational and fun. The kit can be used for basic electronics and skills training, electronics technology instruction, digital circuit teaching, and as a practical training tool for electronics enthusiasts and beginners, enhancing their comprehensive practical abilities. 
Product parameters:
Operating voltage: DC 4-6V
Applicable speaker: 4 ohms 0.5W-5W
Board size: 44*38mm
Debugging Instructions:
Connect the circuit to a 3-6V DC power supply. Adjust RP2 so that the midpoint voltage between Q2 and Q3 is half the power supply voltage; adjust RP3 so that the quiescent current of the power amplifier output stage is 5-8mA; repeatedly adjust RP2 and RP3 until both parameters reach the above values.
Soldering Instructions:
1. Resistors do not have distinct positive and negative terminals, but must be soldered according to the markings on the board.
100Ω resistor color code: Brown-Black-Black-Black-Brown
470Ω resistor color code: Yellow-Purple-Black-Black-Brown
4.7kΩ resistor color code: Yellow-Purple-Black-Brown-Brown
2. The black ring of the 1N4148 diode corresponds to the white ring on the board. The longer lead of the electrolytic capacitor is the positive terminal.
Circuit principle:
Q1 is the driver transistor, providing sufficient drive signal to the power amplifier output stage; R1 and RP2 are bias resistors for Q1; R3, D1, and RP3 are connected in series in the collector circuit of Q1 to provide bias for Q3, keeping it in a slightly conducting state in the static state to eliminate crossover distortion; C3 is a damping capacitor used to eliminate potential self-oscillation in the circuit; Q2 and Q3 are complementary symmetrical push-pull power amplifier transistors, forming the power amplifier output stage; C2 and R4 form a “bootstrap circuit,” and R4 is a current-limiting resistor.
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