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100W MOSFET Power Amplifier

The circuit diagram shows a single channel of my simple MOSFET power amplifier.For stereo applications two identical units would be required.

Although this amplifier was designed with simplicity and ease of construction as aprimary goal, do not be mislead by its simplicity, it will compete with some of the

best amplifiers around.

ha!e decided to ma"e the board !ery compact and included the rese!oir caps andrectifier bridge on board therefore only a power transformer is needed to ma"e itwor".

The output power is related to the power transformer rating that you choose to use.The table below shows appro#imate $MS power output for a particular transformerrating. The amplifier is stable with a supply !oltage as low as %&'()*+, but thiswould be rather pointless as the power output will be only about watts.

Transformer VAC VA Rating RMS Output

24 - 0 - 24 120 50 Watt 8 Ohms

30 - 0 - 30 180 75 Watt 8 Ohms

35 - 0 - 35 226 100 Watt 8 Ohms

f you are planning a stereo amplifier use two seperate power transformers, one foreach channel as it does ma"e for a far better sounding amplifier.

The circuit is !ery simple and uses two M-SA /or 0+ +1 as a differential inputpair followed by 0* '23&'4 as differential )AS stage while a pair of 0* '54&'4 are

used as a current mirror.nterestingly, adding the current mirror made no difference to distortion, but

reduced the *+ offset to less than (4m). The impro!ement was noteworthy.

The MOSFETS are 6itachi lateral de!ices, (S7'48 /9&+hannel1 and (S:'( /-&+hannel1.These are designed specifically for audio, and are far more linear than the morecommon switching de!ices that many MOSFET amps use.;nfortunately, they are not cheap, but their performance in an audio circuit fare#ceeds !ertical MOSFETS or 6E

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Typical Amplifier Performance:

Maximum Output:

? '44 watts rms into 8 Ohms? '@4 watts rms into 5 Ohms

Audio Frequency Linearity:

? (4 6 & (4 "6 /%4, &4. d01

Closed Loop Gain:

? 2( d0

Hum and Noise:

? &3( d0 /input short circuit1

Output Offset Voltage:

? Bess than '2 m) /input short circuit1

!ase Linearity:

? Bess than '2 4 /'4 6 & (4 "61

Harmonic "istortion:

? Bess than 4.448C at any power le!el

#M "istortion:

? Bess than .4'C at ma#imum power

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R19 2 0E22 Resistor 5 WattR25-------------------------------------------------------------

C3 2 100N 5_0 mmC7

-------------------------------------------------------------R24 1 10E Resistor 1 Watt

-------------------------------------------------------------R8 1 10K Resistor 250mW

-------------------------------------------------------------C1 1 10u 06 mm

-------------------------------------------------------------R9 2 1K0 Resistor 250mW

R10-------------------------------------------------------------

R14 1 1K2 Resistor 250mW-------------------------------------------------------------D1 2 1N4148 DSCD2-------------------------------------------------------------D3 D4 D5 D6 4 1N5404 DSC-------------------------------------------------------------R23 1 2K2 Resistor 250mW-------------------------------------------------------------

Q3 1 2S162 !"#-3#-------------------------------------------------------------Q5 1 2SK1058 !"-3#-------------------------------------------------------------R12 2 3K9 Resistor 250mWR13-------------------------------------------------------------C8 2 4700u 25 mmC9-------------------------------------------------------------R5 2 470E Resistor 250mWR6-------------------------------------------------------------

C4 1 470# 5_0 mm-------------------------------------------------------------

R3 1 39K Resistor 250mW-------------------------------------------------------------

R2 4 47K Resistor 250mWR15

R16-------------------------------------------------------------

C2 1 470u 10 mm-------------------------------------------------------------

C5 2 82# 5_0 mmC6-------------------------------------------------------------

Q9 2 $D139-10 !"-126Q10-------------------------------------------------------------

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Q7 2 $D140-10 !"-126Q8-------------------------------------------------------------Q1 2 %#S&56 '$C556( !"-92Q12-------------------------------------------------------------