The drawing of this power amplifier, was published in the magazine Elektor at 12/95. This amplifier uses a completed the NE5534, in its input.Good refrigeration of power transistors must be done with one good heatsink, capable dimensions, which probably it needs help from one Fan, because the temperature goes up enough, when the amplifier work in complete power, for big time distance and with low load near in the 4 ohms.
Thus it should we degrade the high voltage of power supply, in ±15V, that needs the IC1. This becomes with the help of R7,9 and Diodes Zener D1,2. In the input exist a High-pass filter C1-R3 and low-pass filter R2-C2, so that is limited the bandwidth of frequencies of unit of entry, in a concrete bandwidth. The IC1 function as differential amplifier, which the not inverting input (+), work as central node of total feedback. The voltage of feedback from the exit, is applied in the node R4-,R5, via the R6. The compensatory becomes from capacitors C4, C5 and C12, while the gain is appoint by resistors R6, R5, via R6 (X40). Transistors Q1, Q2 works in Class A and the current that elapse from in them is 10mA, (is determined by resistors R10,14). In the exit exist the power transistors Q8,9,10,11 which work in Class AB, (is regulated by transistor Q3 and the trimmer TR1, in current of calm 100mA, for each one power transistor in the exit, that correspond in fall of voltage 27mV, above in resistors R25,26,27,28). In order to we achieve the biggest possible thermic stability, should transistors Q1,2,3,6,7 be placed above in heatsink, with the power transistors. The diodes D9-10 protect the output stage, from reverse voltages, that can be created from the load. The R29 and the C18, shape one classic network of Boucherot, which improve the stability in the high frequencies. The inductor L1, (is constituted by 15 coils wire of diameter 1mm), protect the exit of amplifier from problems, because existence of capacitive load. The R30, ensure the not questioning (because inductor), passage of square pulses. The build of amplifier does not present difficultie for somebody that has a certain experience in the sector.The amplifier will need two power supply, one for each channel. Good it is we protect the exit of amplifier, with a circuit of protection.
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