This has been the first simple MOSFET amplifier circuit for me. It is a quite complete circuit. As a 60 watts power amplifier, this is sufficient for normal use in my home. The circuit may be outdated.
It has several advantages. Try to read, then you will like it. The most important is the durability of the amplifier.
The MOSFET power amplifier is the answer to the above problems. The two main features.
- No problem with the Thermal Breakdown as like a normal transistors circuit. It can be used with all load types, Without fear of damage, the output power the only reduced.
- Do not need the protection as a plain transistor circuit so to work continuously.
Do you interest in it? Let’s learn it in this circuit below.
How this circuit works
See in the circuit.
The signal from a tone control circuit is entered to pass the RF filter circuit. They consisting of C3 and R2 into the base of the transistor (Q1). It is connected with Q2 as the Differential amplifier circuit.
We use the low noise transistors, BC556 PNP type. Then, the output from Q1, Q2 will be fed to the differential amplifier circuit, series second. They consisting of the Q4, Q5 (2SC1775).
The transistor Q3 and D1 act as the active collector load, to get the output signal in a push-pull model. To drive the gate of the transistor output Q8(2SK143) and Q9(2SJ49).
And at the gate of both power MOSFETs, it has diodes D2-D5 attach to protects the overdrive.
Because MOSFET has distortion very low. So the negative feedback circuit has a signal is 45 dB only. It is fed from the output pass to R8, R8, C4 comes to the base pin of the Q8, Q9.
Using low feedback as above. It will help to the distortion at the low overload point is lower than a normal transistor circuit that used a feedback up to 60 dB.
Then, the wire is connected from the power MOSFET to the input section circuit. We connect to pass a decoupling electronic circuit, to help of low distortion is all every value power output. And the signal-noise ratio is better, too.
Because the MOSFET transistor circuit has a future of the Negative Temperature to the coefficient. Thus, this circuit so does not need to set an idle current, the current circuit is between only 50 mA.
MOSFET Amplifier power supply
The characteristics of the power supply as shown in the figure below.
Build this circuit
All equipment installed on the PCB as shown in Figure below. PCB layout and The position of the device on a component layout.
You should check the accuracy and neatness, the Soldering point close to the point. Then, connect the power MOSFET. The wiring should be used a square of 0.5 mm at a minimum, as short as possible.
And then to the power supply circuit. Then connect to the loudspeaker. And the input signal from the tone control circuit was also used.
The shopping list
0.5W Resistors, tolerance: 1%
R2, R5: 2.7K
R6: 150 ohms
R7, R10: 15K
R11, R12: 100 ohms
R13: 330 ohms
R9: 220 ohms
R14, R16: 120K
R15, R17: 4.7K
R18, R19: 560 ohms
R20, R21: 10 ohms 1watts
C1: 2.2uF 50V
C4: 220uF 25V
C6, C8: 47uF 50V
MKT (Metallized Polyester Film) or MKP (metalized polypropylene Capacitors
C2: 100pF 63V
C3: 10pF 63V
C5, C13, C14: 0.1uF 63V
C12: 0.047uF 100V
C10, C11: 68pF 63V
Semiconductors and others
Q1, Q2, Q5, Q7: BC556, 60V 0.1A, PNP TO-92 Transistor
Q3, Q4: 2SC1775
Q6: BC546, 60V 0.1A, PNP TO-92 Transistor
Q8: 2SK134 *read text
Q9: 2SJ49 *read text
D1, D2, D3: 1N4148, 75V 150mA Diodes
L1: 18 AWG on 20T DIA. 5mm.
Now you may be a problem in creating this project. Because buying power MOSFET 2SK134 +2SJ49 is very difficult.
Or use others instead of 2SK135+2SJ50 is cheaper than the same shape. Or use this number instead of IRFP240 + IRFP9240 different shapes(Plastic body).
I do not know the quality of the sound. But friends said the sound is good and cheap as well.
Or other friends recommend this number: BUZ901 + BUZ906.
It will available the same.
You may like these circuits, too.
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8 thoughts on “First Simple MOSFET Amplifier Circuit using 2SK134 & 2SJ49”
Thanks very much for circuit diagram.But no details of winding of L1 coil parallel with R20 resistor.Please mention that.
winding of L1 coil:
Using 1mm wire runing 10 turns over a pencil
Thank so much @Patrick
HOW DO I CREATE PREAMP WITH MJE340 AND MJE350 THE OUTPUT IS J162 AND K1508
If I found is as described above a pre-amp.
I will immediately bring it to the blog.
You may have to wait longer. Apologize in advance.
To the circuit diagram of the “First simple mosfet amplifier circuit by K134+J49”:
There is missing a connection to the ground at the lower side of the speaker!!!
Yes Imre Matrai.
The resistor of R20 is missing in parallel with L1.
R21 is present.