Umzch hi fi on field-effect transistors. Wideband UMZ with low distortion. Old but golden
Low-frequency amplifiers are very popular among radio electronics enthusiasts. Unlike the previous scheme, this power amplifier based on field-effect transistors consists mainly of transistors and uses an output stage that, with a bipolar supply voltage of 30 volts, can provide up to 70 W output power on speakers with a resistance of 4 Ohms.
Schematic diagram of an amplifier using field-effect transistors
The amplifier is assembled on the basis of an operational amplifier TL071 (IO1) or any similar one, which creates the main amplification of the differential signal. The amplified low-frequency signal from the output of the op-amp, most of which flows through R3 to the midpoint. The remainder of the signal is sufficient to be directly amplified by the IRF9530 (T4) and IRF530 (T6) MOSFETs.
Transistors T2, T3 and their surrounding components serve to stabilize the operating point of the variable resistor, since it must be correctly set in the symmetry of each half-wave across the amplifier load.
All parts are assembled on a single-sided printed circuit board. Please note that three jumpers must be installed on the board.
Amplifier settings
Setting up the amplifier is best done by applying a sinusoidal signal to its input and connecting a load resistor with a value of 4 ohms. After this, resistor R12 is installed in such a way that the signal at the output of the amplifier is symmetrical, i.e. the shape and size of the positive and negative half-waves were the same at maximum volume.
The figure shows the circuit of a 50 W amplifier with MOSFET output transistors.
The first stage of the amplifier is a differential amplifier using transistors VT1 VT2.
The second stage of the amplifier consists of transistors VT3 VT4. The final stage of the amplifier consists of MOSFETs IRF530 and IRF9530. The amplifier output is connected through coil L1 to an 8 Ohm load.
The chain consisting of R15 and C5 is designed to reduce noise levels. Capacitors C6 and C7 are power filters. Resistance R6 is designed to regulate the quiescent current.
Note:
Use bipolar power supply +/-35V
L1 consists of 12 turns of insulated copper wire with a diameter of 1 mm.
C6 and C7 should be rated at 50V, the remaining electrolytic capacitors at 16V.
A heatsink for the MOSFETs is required. Dimensions 20x10x10 cm made of aluminum.
Source - http://www.circuitstoday.com/mosfet-amplifier-circuits
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