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G8MNY > TECH 07.07.05 12:20l 73 Lines 2949 Bytes #999 (0) @ WW
BID : 53287_GB7CIP
Read: GUEST OE7FMI
Subj: Mic DJ Preamp
Path: DB0FHN<DB0MRW<DB0WUE<DK0WUE<7M3TJZ<ON0AR<GB7CIP
Sent: 050707/0723Z @:GB7CIP.#32.GBR.EU #:53287 [Caterham] $:53287_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (New Jun 05)
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.
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄ470ÄÄ<+
C1 R1 L1 FB ³ C6³+ R6
u47 10K - - 3³\³8 half ===100u
ÚÄÄ´ÃÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄ())))ÄÄÂÄÄÄÄ´+`\LF353 +10u ³
³ Polly ³ C2 10u+ R4 ³ ³IC1`>ÄÄÄÂÄÄ´ÃÄ)Ä68ÄÂÄ>
³ ³ ÚÄ´ÃÄÄÄ1KÄÄÄÂÄÄ)ÄÂÄÄ´- /' 1 ³ C7 ³ R7 ³
³ ³ u47ÃÄÄÄÄ¿ u1=== ³ ³ 2³/³4 ³ ³ ³ O/P
50ê-1K ³ C3=== BASS C4 ³ ³ ³ ³ GAIN ³ ³
MIC ³ ³ ÚÄ>CUT 68 ³ ÀÄÄÄÄ)Ä4K7Ä>50K ³ ³
³ R2 ³ ³ 5K R3 ³ C5 ³ R5 ³ ³
³ 10K ³ ³ ³ === n1 ³ ³ R8
³ ³ ³ ³ TREBLE³ ³ ³ 100K
³ ³ ³ ³ ÚÄ>LIFT ³ ³ ³ ³
³ ³ ³ ³ ³ 5K ³ ³ ³ ³
ÀÄÄÄÄÄÄÄÁÄÄÄÄÁÄÁÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÁÄ>
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 bass C1 = 5uF.
R1 + R2 Bias the amp to 1/2 power rail & set 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 C2 = 100u
C3 & Bass Cut control give up to -6dB/O additional bass cut.
C3 & R3 + Treble Lift Control, give up to +6dB/O treble boost.
C7 DC decouples O/P.
R7 sets the O/P Z to 68ê.
R8 discharges C7 if needed.
TONE CONTROL GRAPHS (measured)
dBs
+18¿ / MAX
+15´ Slope /..
+12´ +6dB/O /'Gain: TREBLE
+9´ /' @ Max : LIFT
+6´ /' :
+3´ /' MIN
0´ ___...-------------------
-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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