25W High quality Mosfet audio amplifier circuit, no need a preamplifier.
Circuit diagram:
Parts:
| R1,R4 = 47K | 1/4W Resistors |
| R2 = 4K7 | 1/4W Resistors |
| R3 = 1K5 | 1/4W Resistors |
| R5 = 390R | 1/4W Resistors |
| R6 = 470R | 1/4W Resistors |
| R7 = 33K | 1/4W Resistors |
| R8 = 150K | 1/4W Resistors |
| R9 = 15K | 1/4W Resistors |
| R10 = 27R | 1/4W Resistors |
| R11 = 500R | 1/2W Trimmer Cermet |
| R12,R13,R16 = 10R | 1/4W Resistors |
| R14,R15 = 220R | 1/4W Resistors |
| R17 = 8R2 | 2W Resistor |
| R18 = R22 | 4W Resistor (wirewound) |
| C1 = 470nF | 63V Polyester Capacitor |
| C2 = 330pF | 63V Polystyrene Capacitor |
| C3,C5 = 470µF | 63V Electrolytic Capacitors |
| C4,C6,C8,C11 = 100nF | 63V Polyester Capacitors |
| C7 = 100µF | 25V Electrolytic Capacitor |
| C9 = 10pF | 63V Polystyrene Capacitor |
| C10 = 1µF | 63V Polyester Capacitor |
| Q1-Q5 = BC560C | 45V100mA Low noise High gain PNP Transistors |
| Q6 = BD140 | 80V 1.5A PNP Transistor |
| Q7 = BD139 | 80V 1.5A NPN Transistor |
| Q8 = IRF532 | 100V 12A N-Channel Hexfet Transistor |
| Q9 = IRF9532 | 100V 10A P-Channel Hexfet Transistor |
Power supply circuit diagram:
Parts:
| R1 = 3K3 | 1/2W Resistor |
| C1 = 10nF | 1000V Polyester Capacitor |
| C2,C3 = 4700µF | 50V Electrolytic Capacitors |
| C4,C5 = 100nF | 63V Polyester Capacitors |
| D1 | 200V 8A Diode bridge |
| D2 | 5mm. Red LED |
| F1,F2 | 3.15A Fuses with sockets |
| T1 | 220V Primary, 25 + 25V Secondary 120VA Mains transformer |
| PL1 | Male Mains plug |
| SW1 | SPST Mains switch |
Notes:
Can be directly connected to CD players, tuners and tape recorders. Simply add a 10K Log potentiometer (dual gang for stereo) and a switch to cope with the various sources you need.
Q6 & Q7 must have a small U-shaped heatsink.
Q8 & Q9 must be mounted on heatsink.
Adjust R11 to set quiescent current at 100mA (best measured with an Avo-meter in series with Q8 Drain) with no input signal.
A correct grounding is very important to eliminate hum and ground loops. Connect in the same point the ground sides of R1, R4, R9, C3 to C8. Connect C11 at output ground. Then connect separately the input and output grounds at power supply ground.
Technical data:
Output power: well in excess of 25Watt RMS @ 8 Ohm (1KHz sinewave)
Sensitivity: 200mV input for 25W output
Frequency response: 30Hz to 20KHz -1dB
Total harmonic distortion @ 1KHz: 0.1W0.014% 1W 0.006%10W0.006%20W0.007%25W0.01%
Total harmonic distortion @10KHz: 0.1W 0.024%1W0.016%10W0.02%20W0.045%25W0.07%Unconditionally stable on capacitive loads
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