This is a 25 Watt basic power amp that was designed to be (relatively) easy to build at a reasonable cost. It has better performance than the standard STK module amps that are used in practically every mass market stereo receiver manufactured today. When I originally built this thing, it was because I needed a 25 Watt PC amp and did not want to spend any money. So I designed around parts I had in the shop.
Parts:
R1 = 47K R2 = 4K7 R3 = 1K5 R4 = 47K R5 = 390R R6 = 470R R7 = 33K R8 = 150K R9 = 15K R10 = 27R R11 = 500R-1/2W R12 = 10R R13 = 10R R14 = 220R R15 = 220R R16 = 10R R17 = 8.2R-2W R18 = 22R-4W(wirewound) C1 = 470nF-63V C2 = 330pF-63V C3 = 470µF-63V C4 = 100nF-63V C5 = 470µF-63V C6 = 100nF-63V C7 = 100µF-25V C8 = 100nF-63V C9 = 10pF-63V C10 = 1µF-63V C11 = 100nF-63V Q1 = BC560C Q2 = BC560C Q3 = BC560C Q4 = BC560C Q5 = BC560C Q6 = BD140 Q7 = BD139 Q8 = IRF530 Q9 = IRF9530
Parts:
R1 = 3K3-1/2W C1 = 10nF-1000V C2 = 4700µF-50V C3 = 4700µF-50V C4 = 100nF-63V C5 = 100nF-63V D1 = 200V 8A Diode bridge D2 = 5mm. Red LED F2 = 3.15A Fuses with sockets 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 connected in series to Q8 Drain) with no input signal. * A correct grounding is very important to eliminate hum and ground loops. Connect to the same point the ground sides of R1, R4, R9, C3 to C8. Connect C11 to output ground. Then connect separately the input and output grounds to power supply ground. * An earlier prototype of this amplifier was recently inspected and tested again after 15 years of use. Results, comments and pictures are shown here.
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