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7. CIRCUIT DESCRIPTIONS
For details of the circuit of the CT-F950, refer
to the block diagram on Page 13 and also the
overall schematic diagram on Page 54.
7 . 1 R E C O R D I N G A N D P L A Y B A C K C I R C U I T
Playback Equalizer Amplifier
The playback equalizer amplifier is an NFB type
amplifier which uses a low-noise high-gain mono-
l i t h i c I C ( A N 3 7 0 ) .
P l a y b a c k F l a t A m p l i f i e r ( O r o : , O r o + )
The playback flat amplifier is a single transistor
amplifier possessing flat frequency characteristics.
It is used to amplify the output of the playback
equalizer amplifier. A trap circuit is used at the
input side to prevent entry of the recording bias.
Buffer Amplif ier (Oros, Oroo )'
The buffer amplifier is an emitter follower type
circuit which is used to take the output of the
Dolby
NR
amplifier to the LINE OUTPUT
terminals.
rc (P A4 0 0 1 )
T h e P A 4 0 0 1 w a s d e v e l o p e d b y P I O N E E R a s a
system IC for use in tape decks. It contains a
microphone
amplifier, headphone amplifier, flat
amplifier and recording amplifier.
Its block dia-
gram is shown in Fig. 7-1.
O U T
t N
O U T
1 4
1 3
1 2
1 1
. t o
9
%
cr-Fs|5cl
M i c r o p h o n e A m p l i f i e r
T h e m i c r o p h o n e a m p l i f i e r c o n s i s t s o f t h e m i c r o -
p h o n e a m p l i f i e r s e c t i o n o f t h e P A 4 0 0 1 . I t h a s a
g a i n o f a b o u t 2 8 d 8 .
7 . 2 T A P E S E L E C T O R C I R C U I T
T h e C T - F 9 5 0 h a s b e e n d e s i g n e d t o u s e m e t a l ,
C r O z , F e - C r a n d n o r m a l t a p e s . T h e t a p e s e l e c t o r
c i r c u i t ( s e e F i g . 7 - 2 ) i s s w i t c h e d t o s u i t a b l e e q u a l -
i z e r a n d b i a s l e v e l s a c c o r d i n g t o t h e t y p e o f t a p e
e m p l o y e d . T h i s s w i t c h i n g , p l u s t h e t a p e i n d i c a t o r
( C r O z / N I E T A L ) s w i t c h i n g i s p e r f o r m e d b y t h e
T A P E s w i t c h S r : o r .
P l a y b a c k E q u a l i z e r S w i t c h i n g C i r c u i t
The
playback
equalizer may be switched to
e i t h e r
o f
2
p o s i t i o n s :
7 0 s s e c f o r
M E T A L /
C r O z , F e - C r a n d 1 2 0 s s e c f o r S T D .
l V h e n t h e
T A P E s w i t c h S r r o r i s i n t h e I V I E T A L p o s i t i o n
( o r C r O z , o r F e - C r p o s i t i o n s ) , a b i a s c u r r e n t f l o w s
f r o m D r o e ( o r D r r r o r D r r o ) t o Q r o r v i a R r r z ,
resulting in the transistor being turned on.
The
C r r q a n d R r r s s e r i e s c i r c u i t i s t h u s c o n n e c t e d t o
t h e p l a y b a c k a m p l i f i e r t o s e t u p t h e 7 0 g s e c e q u a l -
i z e r a m p l i f i e r . W h e n S r : o r i s s w i t c h e d t o t h e S T D
p o s i t i o n , Q r o r i s t u r n e d o f f , t h e r e b y r e v e r t i n g t o
t h e 1 2 0 1 . r s e c e q u a l i z e r a m p l i f i e r .
Recording Bias Generator and Bias Selector Circuit
Metal tapes require a bias current of about
t w i c e t h e l e v e l o f t h e b i a s r e q u i r e d f o r c o n v e n -
t i o n a l S T D t a p e s . F o r t h i s r e a s o n t h e p u s h - p u l l
generator output is amplified by a bias amplifier
( c o m p o s e d o f
s t e p - u p t r a n s f o r m e r s L r o r
a n d
L t o z p l u s
c o u p l i n g a m p l i f i e r s Q r o o a n d Q r o z )
prior to being applied to the head.
The bias
amplifier
input
may
be adjusted by the front
panel BIAS control.
Whereas more conventional
bias controls vary the B voltage of the oscillator,
the system employed in the CT-F950 also varies
the erasure current at the same time. Since erasure
efficiency
is a particular
problem
with
metal
tapes, the CT-F950
has been designed to also
vary the secondary side of the oscillator trans-
f o r m e r .
Bias switching for each type of tape is achieved
t h r o u g h t h e T A P E s w i t c h S r r o r . B i a s
l e v e l i s
changed by first maintaining a constant oscillation
l e v e l b y f u z o , a n d t h e n c h a n g i n g t h e v o l t a g e b y
inserting resistors in parallel. The parallel connect-
ed resistors involved are R:zo and Vfuor
for metal
t a p e s , R r z z a n d V R r o z f o r C r O z , a n d R r z a a n d
V R : o r f o r F e - C r a n d S T D .
O U T
I N
1 6
1 5
7 - 1
B l o c k d i a g r a m o f
8
G N D
o u r ( t o p v t e w )
PA4001
Headphone Amplifier
The headphone amplifier consists of the head-
phone amplifier section of the PA4001. This is a
complimentary amplifier having a gain of approxi'
mately
7.4d8.
The headphone output
is taken
off a resistive voltage divider.
6 7
I N
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