Replacing the carbon microphone. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Replacing the carbon microphone. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Telephony

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When operating telephone sets of the second and third complexity groups with carbon microphones, a drop in sensitivity is often observed. This is due to the sintering of charcoal particles, which causes a violation of the purity of the sound and distortion in the form of crackling and noise. Currently, many circuits have been developed to replace carbon microphones. The sound quality is improved by an order of magnitude.

On fig. 1 shows a diagram using a dynamic microphone MDM-7. The amplifier in the circuit is made three-stage, it is desirable to select transistors with a high gain.

On fig. 3 shows the amplifier circuit for the MKE-3 condenser microphone. The scheme, when repeated, showed very stable operation. On fig. 4 shows an amplifier diagram for a miniature microphone of the MKE-333B type ("Pine"), and, finally, in fig. 2 shows a diagram where a 1014KT1A telephone key is used as an amplifying element. With the MKE-3 microphone, the circuit has a sensitivity of about 400 ... 500 mV / Pa, which ensures good audibility.

Rice. 1. Scheme for replacing the carbon microphone

Replacing the carbon microphone
Rice. 2. Scheme for replacing a carbon microphone using a key KR1014KT1A

Rice. 3. Scheme for replacing the carbon microphone

Rice. 4. Scheme for replacing the carbon microphone

Publication: cxem.net

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