The following is a 70W amplifier based on a popular TDA7294 chip. Main technical characteristics of the amplifier are as follows: input resistance – 22 kOhm input voltage – 750 mV nominal output power at 4 ohms and THD 0.5% – 70 Watts Frequency Range – 20 … 20000 Hz supply voltage – ± 27 V, quiescent current – 60 mA. The amplifier has a built-in thermal protection, and protection against overload and short circuit in the load. For “soft” switching amplifier is SA1. Switch can be powered from a bipolar unregulated power supply. Power AC Transformer – 250-A, the secondary winding should be designed to current than 5A.
Details of the amplifier are mounted on a printed circuit board (Fig. 3) of the bilateral foiled fiberglass dimensions 50×35 mm board assembly shown in Fig. 4. For installation use resistor-0.25, capacitors C4-C7, CIO – imported analogs C50-35 and K73-17 (the rest). As SA1 apply any miniature push button switch.
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