Microphone preamplifier (RJ4558) modified into headphone amplifier ----- RJ4558 Preamplifier

Keywords: microphone preamplifier (RJ4558) modified into headphone amplifier Be The circuit is as shown in the figure, and the microphone signal is fed into IC1 (JRC4558) 3, 5 feet, 5 feet, from 1, 7 foot output, R6, C4 and R13, C8, respectively, from 1, 7 foot output, R6, C4 and R13, C8, respectively The volume adjustment is performed on the respective volume potentiometers W1, W2, and the two signals are added to the IC2 after the IC2 is mixed, and the two signals are mixed. The circuit is powered by a + 12V power supply. This part of the circuit is separately designed as a small circuit board, and is mounted on the inside of the panel with the microphone socket, which is convenient for modification. The element can be modified into a high-fidelity headphone amplifier, and the specific steps are as follows: 1, cut the copper foil in the figure, remove C1, C5, R4, R11, C4, and C8. 2, put the C1 and C5 from 10 μF capacitance, R4, R11 of the original C9, C11 by 1 kΩ electrical resistance, 5.6 kΩ resistor, C2, and C6 by 1 kΩ electrical resistance, C2, and C6 by 1 kΩ electrical resistance. The C8 is replaced by a 4.7μF capacitor to 220μF; short-fitting resistors R6, R13.3, using the original microphone volume potentiometer as the volume adjustment of the headphone amplifier. Take a paragraph of high quality double-core shield lines that are connected to the AV board on the AV board, respectively, and the upper end of W1, W2, respectively, the potentiometer center joints are connected to R1, R8 as signal input. If the audio is too large, use R1, R2 and R8, R9 to make an attenuation circuit, and the method is to increase the R1 and R8 resistance. 4. Make a headphone socket with the microphone jack on the machine. The first type of microphone socket is replaced with a standard ∮ 6.25mm stereo headphone socket, and the two points of A, B are connected to the socket R, and the contacts, respectively. The next thing is audition, feeling good for sound quality. The modification of this method does not have to increase many components, and there is no adverse effect on the function of the original machine. If you are interested, you may wish to try.

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