Situations when you need to amplify the sound, but there is no microphone at hand, do not happen so rarely. A homemade microphone can help out. Just like a professional one, it can be connected to a computer or a sound recording device.
Necessary
- - shielded audio cable;
- - high impedance earphone;
- - low impedance scientist (you can use a dictaphone or a player);
- - radio broadcast speaker;
- - sound transformer;
- - soldering iron;
- - rosin;
- - tin;
- - insulating tape;
Instructions
Step 1
The microphone can be made from a high-impedance earpiece, which is used in headphones. To do this, use a shielded cable to connect it to the appropriate connector of the amplifier or mixing console. Such a microphone is quite suitable for broadcasting or recording speech. But for recording or amplifying a piece of music, the quality will be insufficient. If you want a high-quality wide-range microphone, make it out of a radio-point broadcast speaker.
Step 2
Take the radio broadcast speaker and open its case. Inside, in addition to the speaker itself, you will also see an output speaker and a transformer, as well as a variable resistance resistor. You don't need the resistor now, so unsolder it from the circuit and remove it from the case. Connect the speaker to the transformer directly.
Step 3
Unsolder the plug and wire from the high-impedance winding of the transformer and, in their place, connect a shielded wire with the appropriate connector for switching on to the microphone jack of the recording or amplifying device.
Step 4
This microphone can be slightly improved. For example, you can screen it. Cover the inside of the translator housing with steel sheet or foil paper. You can use, for example, foil from cigarette packs. Make electrical contact between this shield and the braided shield of the audio cable, for example with a screw and a contact strip. This will eliminate interference from external electromagnetic fields.
Step 5
The sound quality of such a microphone can also be improved. Connect a tunable RC filter in series with the high impedance winding of the transformer. This filter consists of a 510pF capacitor in parallel and a 1mΩ variable resistance. Attach the resistor to the front panel of the radio in the place of the previously removed volume control. Solder the filter and, connecting to the amplifier, select the filter impedance for the best sound quality.
Step 6
In a circuit with a matching transformer, you can use any low-impedance speaker, as well as an output transformer from any tube receiver. Instead of a speaker, you can use low-impedance headphones, including those from a telephone set or a player. If you take a miniature headphone from the player, then the whole structure can be made portable by placing the headphone itself in a metal tube and styling it like a corded microphone. In this case, place the step-up transformer in the immediate vicinity of the amplifier. Make all connections in this structure with shielded wire.
