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Power MOS Transistor HiFi Amplifier

Power MOS Transistor HiFi Amplifier

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Power MOS Transistor HiFi Amplifier

Although they have already been used for several years in the output stages of high-fidelity amplifiers, power MOS transistors appear to be wrongly reserved for high-end hardware. This realization is there to prove the contrary since it is a high fidelity power amplifier using such transistors. If you have already looked at the diagram, you could see that it was neither complex nor costly to achieve.
In spite of this simplicity, it can deliver an effective power of 60 W on a 4 ohm loudspeaker when powered under ± 30 V. Its bandwidth ranges from 5 Hz to 100 kHz to 0 / - 1 dB , And the harmonic distortion at 1 kHz is less than 0.1% of a few milliwatts at maximum power.
It is a classic of its kind, which can be found, with slight variations, in numerous technical publications. It owes its simplicity to the fact that MOS transistors require virtually no control current as opposed to bipolar power transistors.
The input stage is of the differential type, which facilitates the application of an easy feedback feedback via R6 / R7 and T2, the ratio R6 / R7 naturally fixing the gain of the amplifier.
The next stage made with T4 is none other than the driver of the output MOSs while T3 is conventionally mounted as a pseudo diode in order to allow an adjustment of the quiescent current by means of the potentiometer P1.
Our printed circuit supports all the components of the assembly except for the choke 1 which must be placed on the wire connecting the loudspeakers. The power MOS transistors, in the TO 220 package or the like, are mounted at the edge of the circuit so that they can be screwed to a radiator or to a metal face of the housing when operating. This assembly is to do with the traditional insulating accessories and silicone grease to improve the thermal conduction of course. The power supply may be stabilized or not, but in the latter case it should be ensured that it can not exceed 35 volts. Attention, 60 W on 4 ohms, this still corresponds to a current of nearly 4 A; It is therefore necessary to dimension this power supply, its output chemicals (at least 4,700 MF) and the cables connecting it to our module. These cables will also be the same size for the connection to the speakers since they must also be able to carry this current. The inductor L1 is to be produced by winding with contiguous turns of the enamelled copper wire about 10/10 mm on a carbon resistance of 10 ohms 2 W. The exact number of turns is of little importance whenever the body is covered Of resistance. The quiescent current must be set by P1. To do this, power the amp but do not apply any signal to the input and let the heater for about ten minutes. Then adjust P1 to read a 50 to 60 mA consumption measured in the positive feed wire.
With the values ​​of the indicated elements, the gain of the amplifier is 20, which means that it delivers its maximum power for an input voltage of 700 to 800 mV effective, which is the value currently provided by the amplifiers. Preamplifiers and mixers. This gain can however be increased to a maximum of 100 if necessary by decreasing R7.

Nomenclature of components
T1, T2: BC556
T3, T4: BC546
T5: IRF 530, IRF 630, IRF 633
T6: IRF 9530, IRF 9630, IRF 9633

R1: 4.7 kr
R2, R6: 47 kr
R3: 15 kr
R4: 1.2 kr
R5: 560 r
R7: 2.2 kr (gain of 20) at 470 0 (gain of 100)

R8, R9: 2.7 kr

R10: 680 r
R11: 10kr
R12: 820
R13: 10 r 2 W
L1 (for its realization): 10R 2 W carbon

C1: 220 pF ceramic
C2: 100 uF 15 V chemical radial
C3, C4: 47 fjf 40 V chemical radial
C5, C6: 100 fif 40 V chemical radial
C7: 68 nF mylar

P1: horizontal adjustable potentiometer of 1 kr
Radiator for T5 and T6
10mm enamelled wire for L1

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