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G8MNY > TECH 29.03.04 08:17l 67 Lines 2867 Bytes #999 (0) @ WW
BID : 50466_GB7CIP
Read: DB0FHN GUEST OE7FMI
Subj: Phantom Bal Mic Preamp+Gun Mic
Path: DB0FHN<DB0RGB<OK0PPL<DB0RES<ON0AR<IK1ZNW<GB7CRV<GB7CIP
Sent: 040328/2318Z @:GB7CIP.#32.GBR.EU #:50466 [Caterham] $:50466_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (New 11/03)
Phantom powered Mic Preamp +12 to +48v with balanced 600ê O/P Z.
ÚÄÄÄÄÄÄÂÄÄÄ10KÄÄÄÂÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄ10KÄÄÄÂÄÄÄ270ÄÄ + phase
³ ³ R2 100K ³ ³ R9 ³ R11
³ R1³ ³R3 ³ ³ C6 ³ BALANCED
³ 22K ³ 3³\³8 ÚÄÄÄ)ÄÄÄÄÄ´ÃÄÙ+ PHANTOM
³ ³ ÚÄÄ)ÄÄÄÄÄÄÄij+ \__³ ³ 22u 50v POWER
³+ ³ 1u ³ ÃÄ10KÄÂÄij- / 1³ R10
ÄÁÄ ³ 25v ³ ³ R6 ³ 2³/ ³ ÃÄÄ10KÄÄÄÂÄÄÄ270ÄÄ - phase
ÄÂÄC1 ÃÄÄ´ÃÄÄ´ ³ ÀÄÄÄR7ÄÄÄÙ +³ ³ R12
³100uF ³ C2 ³ ³ ÄÁÄC4 ³
³25v ³+ ³ ³ ÚÄÄÄR8ÄÄÄ¿ ÄÂÄ100u ³
³ MIC ³ ³ ³ 5³\ ³ ³ 40v ³
³ CAPSULE ³ ÃÄÄÄÄÄ)Äij+ \__³ ³ ³
³ ³ ÀÄÄ)Ä10KÄÁÄij- / 7ÀÄÄÄ)ÄÄÄÄ´ÃÄÄÙ
³ ³ ÚÄÄÄ´ R5 6³/³4 ³ C5 +
³ ³ C3 ³ ³ ³ ³ 22u 50v
³ ³10u+ÄÁÄ 100K ³ ³
³ ³ 25vÄÂÄ ³R4 ³ ³
ÀÄÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ Shield
Any 8 dil dual opamp eg CA3240, LM358N, MC1458C, NE5532N, NJM4558,
OPA2604AP, TL072, TL082, etc,
Gain of each phase = R7orR8/10K
Typical values R7=R8= 100K, gives 10x gain/phase, x20 overall gain (26dB).
The polarity of the C2 in series with the electret mic depends on the DC bias
level needed for the perticular mic capsule. So test the relative DC levels
before inserting capacitor.
The value of R9 & R10 can be changed to better suit the phatom powering voltage
eg 12v use 4K7, 48v use 22K.
LF tayloring can be incorperated if C2 in series with the mic can be reduced to
about 0.1uF. Also the 2 O/P Cs (C5,C6) are reduced, values depend on external
load.
WHAT DOES WHAT.
R11&R12 condition O/P Z to approx 600ê, & supply some RFI & spike suppression.
R9&R10 with C4 decouple the DC phantom IC supply from out going line AF.
R2 with C1 decouple the DC supply for the mic.
R1 supplies DC current to the mic.
C2 passes mic AF into R5 load, & hence determins LF responce.
R3,R4 & C3 provide a decoupled « DC rail bias point for the op amp.
R5, R8 & R6, R7 provide the 2 opamp voltage Negative Feed Back, setting gain.
C5 & C6 pass O/P AF into the line.
MAKING A GUM MIC
If the Mic capsule is inserted tightly (sealed) into a long 30mm dia tube that
has holes or slots made down it's length, a very directional gun mic is made,
(over the frequency range where the sound waves are columnmated in the tube).
: : : : : : : : : : : : : : : : : : : sponge windshield
: : -- --- --- --- --- --- --- --- ----
: : [] mic capsule
: : -- --- --- --- --- --- --- --- ---- slotted pipe
: : : : : : : : : : : : : : : : : : :
/QSL
73 de John G8MNY @ GB7CIP
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