HOW TO MAKE - MIKE DESENSITIZER

Many cassette recorders do not have a high level (aux) input; they are meant only for use with microphones. If you try to dub directly from another recorder’s “line” output, or from across the speaker, the relatively high signal level overloads the microphone input, causing severe distortion. Good dubs can be obtained by attenuating the high level signal almost 50 dB, so the attenuated signal is essentially equal to microphone level. This recorder bridging cord provides about 50 dB attenuation in a single, easy-to-handle assembly. Connect resistor R1 in series with the shielded cable hot lead. Connect the free end of R1 to recorder plug PL2 and one end of resistor R2. Fold R2 back adjacent to R1 and solder the free end to the cable shield. Loop a wire from the shield to the PL2 outside (sleeve) terminal. PL1 should match the output jack of the recorder you dub from.

Part List For Mike Desensitizer

PL1, PL2 – Plugs to match existing tape equipment Shielded cable

R1 – 100,000 ohm, 1/4 – watt resistor

R2 - 10,000 ohm, 1/4 – resistor

HOW TO MAKE A HEARING AID?

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DESCRIPTION

Commercially available hearing aids are quite costly. Here is an inexpensive hearing aid circuit that uses just four transistors and a few passive components.

On moving power switch S to ‘on’ position, the condenser microphone detects the

sound signal, which is amplified by transistors T1 and T2. Now the amplified signal

passes through coupling capacitor C3 to the base of transistor T3. The signal is further

amplified by pnp transistor T4 to drive a low impedance earphone. Capacitors C4 and C5

are the power supply decoupling capacitors.

The circuit can be easily assembled on a small, general-purpose PCB or a Vero board. It operates off a 3V DC supply. For this, you may use two small 1.5V cells. Keep switch S to ‘off’ state when the circuit is not in use. To increase the sensitivity of the condenser microphone house it inside a small tube.

This circuit costs around Rs 65.

DOWNLOAD THE CIRCUIT DIAGRAM