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G8MNY > TECH 18.05.07 10:04l 77 Lines 3230 Bytes #999 (0) @ WW
BID : 15014_GB7CIP
Read: GUEST OE7FMI
Subj: Mic DJ Preamp
Path: DB0FHN<DB0RGB<DB0MRW<DK0WUE<SP7MGD<SR1BSZ<CE8FGC<LA2MV<GB7CIP
Sent: 070518/0008Z @:GB7CIP.#32.GBR.EU #:15014 [Caterham] $:15014_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Updated May 07)
(8 Bit ASCII Graphics use code page 437 or 850)
Here is preamp from mic to high line level with gain control, designed for an
unbalanced close in mic, with top lift & bass cut controls. As it is for close
in mic very low noise it not needed, but a good bass roll off is.
SPECIFICATION
GAIN..... 5 to 50 times.
TREBLE LIFT @ 15KHz 0dB to +15dB
BASS CUT @ 100Hz -3dB to -15dB
I/P Z 5kê suitable for any low Z mic.
NOISE... Very low for 1/2 of a simple low noise op amp.
POWERING +8V to +36V DC powering @ 3 - 5mA (C6 voltage!)
RFI OK for reasonable levels, eg Cellphones/VHF/HF radio.
CIRCUIT
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄ470Ä<+5-30V
C1 R1 L1 FB ³ C6³+ R6
u47 10k - - 3³\³8 half ===100u
ÚÄÄ´ÃÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ(((()ÄÄÂÄÄÄÄÄ´+`\ LF353 +10u ³
³ Polly ³ C2 10u+ R4 ³ ³IC1`>ÄÄÄÄÄÂÄÄÄ´ÃÄÄ)Ä68ÄÂÄÄÄ>
³ 10k ÚÄÄ´ÃÄÄÄÄ1kÄÄÄÂÄÄÄÄ)ÄÄÂÄÄ´- /' 1 ³ C7 ³ R7 ³ O/P
³ R2 ³ u1=== ³ ³ 2³/³4 ³ ³ ³
50ê-1k ³ ÃÄÄÄÄÄ¿ C4 ³ ³ ³ ³ GAIN ³ ³
MIC ³ === BASS 68 ³ ÀÄÄÄÄ)ÄÄ4k7ÄÄ>50k ³ ³
³ ³ C3 ³ ÚÄ>CUT R3 ³ ³ R5 ³ ³
³ ³ u47 ³ ³ 5k ³ === C5 ³ ³ R8
³ ³ ³ ³ TREBLE ³ n1 ³ ³ 100k
³ ³ ³ ³ ÚÄ>LIFT ³ ³ ³ ³
³ ³ ³ ³ ³ 5k ³ ³ ³ ³
ÀÄÄÄÄÄÄÄÁÄÄÄÄÄÁÄÄÁÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄ>0V
WHAT DOES WHAT
R6 & C6 decouple the supply & make sure it is quiet to feed into R1.
C1 is a low noise I/P cap, just big enough to let though 100Hz @ -3dB.
for flatter low bass use C1 = 5uF.
R1 + R2 Bias the amp to 1/2 power rail & determin the I/P Z.
L1 near IC is 10 turns on a ferrite bead & with C5 forms a RF low pass filter.
IC1 is low noise, only 1/2 used here, making pins 3 & 4 ideal for C5.
R5 + 50K Gain with R4, set the gain 5 to 50. (50 is max if U want treble lift)
C2 & R4 give minimum bass roll off. (as did C1). For flatter bass use C2 = 100u
C3 & Bass Cut control give up to -6dB/O additional bass cut.
C4 & R3 + Treble Lift Control, give up to +6dB/O treble boost.
C7 DC decouples output.
R7 sets the output Z to 68ê & gives some protection to the IC.
R8 discharges C7 if needed.
TONE CONTROL GRAPHS (measured)
dBs
+18¿ ,/ MAX
+15´ Slope ,/..
+12´ +6dB/O ,/'Gain: TREBLE
+9´ ,/' @ Max : LIFT
+6´ ,/' :
+3´ ,/'
0´ ___...------------------- MIN
-3´ MIN_.--'"~ ,/'
-6´ .-" ,/'
-9´ /"BASS ,/' Slope
-12´ | CUT/' -6dB/O
-15´ | /'
-18´| |'MAX
ÀÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄ>Freq
20 50 100 200 500 1k 2k 5k 10k 20k
Why Don't U send an interesting Bul?
73 De John, G8MNY @ GB7CIP
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