12W FET audio amplifier  parts list :

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Power MOSFET BD522 and BD512 is now obsolete, so you can use other power MOSFET according to its characteristics. Q1 and Q2 are wired as a pair Darlington transistor that serves as a preamplifier. R3 Preset controls the quiescent current while R2 providing feedback. The output coupled to the speaker through capacitor C4. capacitor C5 Is a power filter andC2 is decoupling capacitor for DC input.

Mosfet Audio Amplifier Parts list :
R1 : 39K
R2 : 560K
R3 : 4.7K Variable
R4 : 10K
C1 : 33pF
C2 : 1uF
C3 : 4.7uF
C4 : 220uF
C5 : 2200uF
D1 : 1N4001
Q1, Q2 : BC107
Q3 : BD512
Q4 : BD522

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Transistors T1 and T2 makes a first differential stage, current source of +/- 1 mA is set by R3. P1 allows a fine tuning of DC voltage at amplifier’s output. Place P1 at it’s half value for first power up, then turn it slowly for a lowest DC output voltage. It is recommended to use a first quality component.

Input sensitivity is 1.2 volts. The gain of 27x is archived by R7/R6. It may be modified by changing R7 value. Transistors T5 and T6 makes the second differential stage. Transistors T3 and T4 works as a current mirror source. They push the second differential stage to drain equal current. Doing so we get a high gain and an excellent linearity. Output MOSFET transistors works in AB class, their quiescient current is set from 50 to 100 mA trough P2. For setting quiescient current, you must set P2 in minimal resistance, place a multimeter in mV DC range accross on R14 or R15 leads, turn slowly the screw untill you read a 16,5 mV value, which correspond to a 50 mA quiescient current. F1 and F2 works as an elementary output short-circuit protection.

The power supply must have a value between 45 and 55 Volts DC (positive and negative). One heatsink with a thermal resistance less of 2° C / W is required. All resistors are 1% metal film 1/4 watt.

Note :
Before connecting a speaker at amplifier output, connect a multimeter at output and look on DC output voltage. This level never may be greater than 50 mV. If it is so, check all amplifier for a mistake. Also, change T2 with another device and check again.

Parts list :
C1 = 2.2 uF MKP, MKT 100 V
C2 = 330 pF ceramic 50 V
C3 = 100 nF MKP, MKT 100 V
C4 = 40 uF 100 V electro-chemical
C5, C6 = 18 pF ceramic 50 V
C7 = 100 nF MKP, MKT 250 V
C8 = 47 uF 100 V)
R1 = 47 K
R 3 = 470 Ohms
R2 = 2K2
R4, R5 = 3K9
R6 = 1 K
R7 = 27 K
R8, R9, R11 = 100 ohms
R10 = 10 K
R12, R13 = 470 ohms
R14, R15 = 0.33 ohm 5 watts
R16 = 10 ohm 3 watt
R17 = 1 K
R18, R19 = 10K
T1, T2, T9, T10 = 2N5401, ZTX558, BC556B (note the different pinout - take care for pin layout)
T3, T4 = BF470, MJE350, 2SB649
T5, T6 = BF469, MJE340, 2SD669
T7 = IRFP240, 2SK1530, 2SJ162, BUZ900DP, BUZ901DP (note the different pinout - take care for pin layout: GDS GSD)
T8 = IRFP9240, 2SJ201, 2SK1058, BUZ905DP, BUZ906DP (note the different pinout - take care for pin layout: GDS GSD)
P1 = 100 ohms (25 laps - 25 turns)
P2 = 2K5 (25 laps - 25 turns)
F1, F2 = 3 T A

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25 Watt power amplifier based MosFet,  can be connected directly to the signal source and does not require pre-amplifier to drive. The amplitude of the input signal must reach the level of 200 mV. This signal is normally present on the linear output recorder, CD player, computer sound card and other devices. To adjust the volume can be placed at the entrance to the potentiometer 10 kohm. Trimmer adjustable quiescent current. It must be within 100 mA.

Technical data:
Output power :  well in excess of 25 Watt RMS @ 8 Ohm (1KHz sine wave)
Sensitivity : 200mV input for 25W output
Frequency response : 30Hz to 20KHz -1dB
Total harmonic distortion @ 1KHz : 0.1W 0.014% 1W 0.006% 10W 0.006% 20W 0.007% 25W 0.01%
Total harmonic distortion @10KHz : 0.1W 0.024% 1W 0.016% 10W 0.02% 20W 0.045% 25W 0.07%
Unconditionally stable on capacitive loads

Power supply for this 25 watts power amplifier based MosFet can be found here.

Parts list :
Resistor
R1,R4 : 47K  1/4W
R2 : 1/4W
R3 : 1K5  1/4W
R5 : 390R   1/4W
R6 : 470R   1/4W
R7 : 33K   1/4W
R8 : 150K   1/4W
R9 : 15K   1/4W
R10 : 27R   1/4W
R11 : 500R   1/2W Trimmer Cermet
R12,R13,R16 : 10R   1/4W
R14,R15 : 220R   1/4W
R17 : 8R2    2W
R18 : R22   4W Resistor (wirewound)
 Capacitor
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
 Semiconductor
Q1-Q5 : BC560C   45V 100mA Low noise High gain PNP Transistors
Q6 : BD140    80V 1.5A PNP Transistor
Q7 : BD139    80V 1.5A NPN Transistor
Q8 : IRF530  100V 14A N-Channel Hexfet Transistor
Q9 : IRF9530 100V 12A P-Channel Hexfet Transistor

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