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R I O E
2 7 K
x
R O 3
1 0 0 x
*
R 1 0 2
2 , 2
3 1 3 k c , / s i c 5 = 2 5 0 p F
F i g . 4 1 . T h e r e c o r d p r e - o m p l i f i e r , s c h e m o t i c .
5.1.2 The record pre-amplifier
The schematic for the record pre-amplifier is shown
i n f i g . 4 l . T h e r e c o r d p r e - a m p l i f i e r i s a t h r e e s t a g e
t r a n s i s t o r a m p l i f i e r . Q l 0 1 a n d Q l 0 2 a r e c o n n e c t e d
i n c o m m o n e m i t i e r c o n n e c t i o n w h i l e Q l 0 3 i s c o n -
nected in common collector connection (emitter fol-
lower).
T h e r e c o r d p r e - a m p l i f i e r i s f u r n i s h e d w i t h o n e
m i c r o p h o n e i n p u t a n d o n e l i n e i n p u t c o n n e c t e d i n
p a r a l l e l . W h e n u s i n g t h e m i c r o p h o n e i n p u t , t h e l i n e
i n p u t i s d i s c o n n e c t e d . T h e i n p u t i m p e d a n c e i s 2 0 0
o h m s , u n b a l a n c e d . T h e i n p u t s e n s i t i v i t y i s . 1 5 m V .
T h e c a p a c i t o r s C i 0 4 , C l 0 7 a n d C i 8 0 a r e f i l t e r c a p a -
c i t o r s f o r r a d i o f r e q u e n c y s i g n a l s .
T h e c o m p o n e n t s R l 0 5 , R l 0 7 a n d R l l 3 f o r m a n e g a -
tive feedback circuit from the emitter of Ql03 to the
e m i t t e r o f Q 1 0 l .
T h e f e e d b a c k c i r c u i t i s f r e q u e n c y i n d e p e n d e n t a n d
i n t r o d u c e d f o r s t a b i l i z i n g t h e a m p l i f i e r .
A n e g a t i v e f r e q u e n c y i n d e p e n d e n t f e e d b a c k c i r c u i t
( R 1 0 5 , R l 0 6 a n d C 1 0 3 ) i s i n t r o d u c e d i n t h e e m i t t e r
c i r c u i t o f Q l 0 l .
T h e o u t p u t s i g n a l f r o m t h e r e c o r d p r e a m p l i f i e r p a s s e s
C l l 0 a n d R l 1 5 v i a t h e c o n t a c t F l l f o t h e V o l u m e
c o n t r o l R l . T h e f r e q u e n c y r e s p o n s e o f t h e r e c o r d
p r e - a m p l i f i e r i s f l a t .
*R rzs
R 1 3 1
120
-J-- 22n
5.1.3 The FM-multiplex filter
R e f . f i g . 4 l . T h e F M - m u l t i p l e x f i l t e r , C 6 , L 5 a n d R 9 ,
i s i n t r o d u c e d t o r e m o v e t h e p i l o t s i g n a l w h i c h m i g h t
a p p e a r o n t h e o u t p u t t e r m i n a l s o f t h e t u n e r d u r i n g
stereo recepiion.
T h e p i l o t s i g n a l i s u s u a l l y a l 9 k c / s s i g n a l b u t i n c e r -
t a i n a r e a s a 3 3 , 3 k c / s s i g n a l i s u s e d w h i c h w i l l n e e d
a s l i g h t m o d i f i c a t i o n o f t h e f i l l e r , r e f . f i g . 4 1 .
5.1.4 The equalizing amplifier in RECORD position
T h e s c h e m a t i c f o r t h e e q u a l i z i n g a m p l i f i e r i n r e c o r d
p o s i t i o n , i s s h o w n i n f i g . 4 2 . T h e r e c o r d a m p l i f i e r i s
a f o u r t r a n s i s t o r a m p l i f i e r .
Q l 0 6 a n d Q I O T i s a c o m p o u n d c o n n e c t e d s t a g e
( D a r l i n g t o n c o n n e c t i o n ) . T h i s c i r c u i t h a s a h i g h i n p u t
i m p e d a n c e a n d h i g h a m p l i f i c a t i o n . Q l 0 8 i s c o n n e c f e d
i n c o m m o n e m i t t e r c o n n e c t i o n a n d Q l 0 9 i s c o n n e c t e d
in common collector connection (emitter follower).
The record equalization is obtained by fhe negative
f e e d b a c k c i r c u i t f r o m t h e e m i t t e r o f Q l 0 9 t o t h e
e m i t t e r o f Q 1 0 7 .
The emitter feedback circuit decreases the amplifica-
t i o n a p p r o x i m a t e l y 3 0 d B i n t h e m e d i u m r a n g e o f t h e
rrequency response.
T h e l o w e r r a n g e o f t h e h i g h f r e q u e n c y r e s p o n s e i s
d e t e r m i n e d b y t h e c a p a c i t o r C \ 2 2 . T h e s e r i a l r e s o n -
a n c e c i r c u i t L l , C l 2 5 a n d R l 3 6 f o r m s t h e h i g h f r e -
quency response.
The low frequency response is obtained by the capa-
c i t o r C I 2 7 a n d t h e r e s i s i o r R 1 4 0 .
C l 8 6 i s i n f r o d u c e d f o f o r m a p a r t o f t h e h i g h f r e q u -
ency response.
The equalization switch is linked fo the speed selector
k n o b , a n d c o r r e c t e q u a l i z a t i o n f o r t h e d i f f e r e n t
s p e e d s w i l l b e o b t a i n e d a u t o m a t i c a l l y w h e n f h e
s p e e d i s c h a n g e d .
The componenis are referred to 7th i.p.s. tape speed.
T h e s p e e d e q u a l i z a t i o n i s o b t a i n e d i n 3 3 / a i . p . s . b y
t h e r e s i s t o r R l 3 4 a n d t h e c a p a c i t o r C 1 2 4 , i n s p e e d
l 7 / a i . p . s . t h e e q u a l i z a t i o n i s o b t a i n e d b y t h e r e s i -
s t o r R i 3 2 a n d f h e c a p a c i t o r C l 2 3 .
The output signal is fed to the record current adiust.
m e n t p o t e n t i o m e t e r R l 4 v i a t h e r e s i s t o r R 1 4 5 .
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F i g . 4 2 . T h e e q u o l i z i n g o m p l i f i e r i n r e c o r d p o s i t i o n , s c h e m o t i c .
, I K
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