• on Audio/Video/Photography
  • Published in issue 11/2003 on page 0
About the article

Directional Microphone

with switchable characteristic

Directional Microphone
The directional microphone published in the July-August 2002 issue of Elektor Electronics does its job, but does not have the right directional characteristic. The authors have developed a new circuit which satisfies all the requirements in practice as well as in theory.The microphone published in the July-August 2002 issue of Elektor Electronics was designed to reduce the risk of feedback when used with a jazz harmonica. However, it does not exhibit the ideal cardioid directional characteristic. It can be shown mathematically that as the characteristic is adjusted from omnidirectional at one extreme to figure-ofeight at the other, it is never strictly cardioid or supercardioid: instead a null is gradually introduced, like a belt being tightened around the omnidirectional response until it becomes a figure-of-eight.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor Members can exclusively download these files for free as part of their Membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Extra info, Update
The equation in the article text on page 26 contains a wrong component reference and should be amended to read: R8 = d / (c x C7)
Resistors:
R1,R3,R39 = 4k?7
R2,R4,R37,R38 = 470?
R5,R15,R26,R32 = 47k?
R6,R7,R28 = 22k?
R8,R16,R17,R18,R31 = 1k?
R9,R24 = 100k?
R10 = 3k?3
R11 = 1k?5
R12,R13 = 1k?1
R14 = 2k?4
R19-R22 = 220k?
R23 = 150k?
R25 = 68k?
R27 = 33k?
R29 = 15k?
R30,R33,R34 = 10k?
R35,R36 = 47?
P1 = 47k? preset
P2 = 1k? potentiometer, logarithmic
Capacitors:
C1,C4 = 2nF2
C2,C5,C8,C13 = 330nF
C3,C6 = 220µF 10V radial
C7 = 47nF
C9,C10,C24 = 100nF
C11 = 150nF
C12 = 220nF
C14 = 470nF
C15 = 680nF
C16,C23 = 1µF 63V MKT, lead pitch 5mm or 7.5mm
C17 = 1µF5 63V MKT, lead pitch 5mm or 7.5mm
C18 = 2µF2 63V MKT, lead pitch 5mm or 7.5mm
C19 = 3µF3 63V MKT, lead pitch 5mm or 7.5mm
C20 = 4µF7 63V radial
C21 = 6µF8 63V radial
C22 = 22µF 40V radial
C25,C26 = 100µF 63V radial
C27 = 470µF 63V radial
Semiconductors:
D1 = zener diode 7.5V 1.3W
D2 = 1N4148
T1 = BC546B
IC1 = TS925IN (ST), e.g., Farnell
IC2 = TLC2272 (Texas Instruments)
Miscellaneous:
K1 = 3-way SIL pinheader + 6.3mm jack socket, chassis mount with separate ground contacts
K2 = 3-way SIL pinheader + XLR plug (male) chassis mount
S1 = 2-pole 6-way rotary switch, PCB mount
S2 = 1-pole 12-way rotary switch, PCB mount
BT1 = 9-V battery 6F22 with clip-on leads
MIC1,MIC2 = electret microphone element (e.g., Monacor MCE2000)
PCB, order code 030046-1, (available from The PCBShop
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