About the article

Directional Microphone

for ‘softer’ instruments

Compared to the other instruments in a band the mouth organ is often not loud enough. Turn up the amplifier, and you risk feedback. What is needed is a microphone with a highly directional response.Microphones that are equally sensitive in all directions have a spherical, or omnidirectional, response pattern. Such microphones respond to the changes in pressure that represent a sound. Pressure is a directionless quantity, and so a microphone with an omnidirectional response pattern can also be used as a pressure transducer (Figure 1a).
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Component list
R1,R5 = 22kOhm
R2 = 10kOhm
R3,R4,R6 = 33kOhm
R7 = 220Ohm
P1 = 22kOhm preset
P2 = 47kOhm preset
P3 = 10kOhm potentiometer, logarithmic law, miniature mono type
C1 = 10µF 63V radial
C2 = 100nF
C3,C6,C7 = 22µF 40V radial
C4 = 100pF
C5 = 1µF 63V radial
IC1 = TL071CP*
Bt1 = 9V PP3 battery with clip-on connector
MIC1,MIC2 = miniature condenser (electret) microphone capsule with rubber holder (e.g. Monacor/Monarch type MCE2000)
3.5mm stereo jack socket or 5-way DIN-socket, chassis mount*
K1 = 6.3mm mono jack socket with integral isolated switch, for chassis mounting
Enclosure with battery compartment (and belt clip), size approx. 102×61×26 mm
* see text
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