# Power amplifier for Loudspeaker 6.5W 8R

## Description

The amplifier of circuit, use negative current feedback. So, the load current depends mainly from the input signal and no so much from the impedance of loudspeaker. The inductor current of loudspeaker develop above in the R7 a voltage. This voltage is drive to the inverting input of IC1, creating thus negative feedback. Total voltage gain of circuit, it depend from the reason of impedance of loudspeaker H1 [ Zo ], to the price of R7. In the circuit the gain is (Zo+R7)/R7 that is to say (8+0.5)/0.5=17.. The connection output of IC1 in the ground, is extraordinary, but in this way, the current of base of transistors Q1, Q2 is provided by the lines of supply and no by the IC1. The calm current of is 50 until 100mA, for operation in Class A and is determined by R2, R3, R5, R6. Transistors Q1-Q2, should be matching, so that are not created big current and voltage of deviation. May it will are change the resistors R2, R3, so that we achieve symmetry of bias. With complete drive, the current of emitter the Q1-Q2 is roughly 500mA. The THD is 0.01% for output power, 6.5W in 8R and voltage supply ± 18V. Elektor’87

## Part List

• R1=10Kohm
• R2-3=130ohm
• R4=68Kohm
• R5-6=1ohm 1W
• R7=0.5ohm 1W
• C1=470nF 100V MKT
• C2=22pF ceramic
• C3-5=100nF 100V MKT
• C4=220nF 100V MKT
• IC1=NE5534
• Q1=BD242C
• Q2=BD241C
• RV1=100Kohm trimmer
• M1=8ohm >20W Loudspeaker