audiphone circuit made ​​of discrete components

Published:2011/5/4 9:33:00 Author:TaoXi | Keyword: audiphone, discrete components | From:SeekIC

1. Principle The audiphone circuit made ​​of discrete components is as shown in figure 1, it is the multi-stage audio amplifier which is composed of a transistor VT1 ~ VT3. The typical RC coupled amplifier is composed of the VT1 and external RC components, this amplifier is the front audio voltage amplifier; the two-stage direct coupling type power amplifier circuit is composed of the VT2 and VT3, VT3's output impedance is low to work with the 8Ω low-impedance headphone. 2. Component selection VT1 and VT2 select the 9014 or 3DG8 silicon NPN low power, low-noise transistor, and the current amplification coefficient is β≥100; VT3 selects the 3AX31 Ge PNP low power transistor, the current Iceo is β≥30. B selects the CM-18W (φ10mm×6.5mm) high sensitivity electret microphone, and it has five levels of sensitivity which are indicated by the color dots: red is -66dB, light yellow is -62dB, dark yellow is -58dB, blue is -54dB, white is ＞-52dB. This device need to use the white dot to have high sensitivity. B can also use the electret microphone with blue dot and high sensitivity.



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