Yamaha CT-7000 Service Manual page 8

CT-7000
BLEND
AUTO CIRCUIT
A weak stereo signal is accompanied
more noise than a monophonic signal of the same
strength. The phase of such noise is opposed in the
right and left channels·, so it is possible to cancel it,
at least in part, through mixing the channels, without
Operation
With the Auto
1. Blend Switch
Since t h e Tr1 bias is positive,
potential at point@
© are below -0.5V, so
Tr5 off. In addition -12V is fed
F ET2, so there is no blend effect.
2. With the Auto
Blend S
a. If the strength of the received signal is less than
40dBJ,L, potential present at input
low, that the outpu t
so
i gh
h raising the potentials at points (Ql and ©to
,
more than -0.5V. This switches Tr2 and Tr4 off
and Tr5 on, and potential almost the value
and Tr3
AUTO TOUCH AFC OFF CIRCUIT &
INDICATOR CIRCUIT
These i r c ui ts turn the AFC off when a s tat i o n is
c
tune d ,
bei ng and als o indicate when tuning is in the
reception r ea of a station, showing that the AFC is
a
off at
the same t i me
merits:
I f C is c on s ta
1. the F
A
t hen ,
that AFC-caused f r e q ue
as s uming
th e a pparent selecti on
su h
c
if there is
ase ,
a c
t h e
dial,
the tuning
d
u ri n g stati on selection, w h ic h
t o
tu ne the nearby station. T o avoid
6
by noticeably
Off
Tr1 switches on and
z e r o Potentials at points
is
.
Tr2 and Tr4 are on, Tr3 and
to the gates of
witc h On
terminal h
i mped an ce from Tr1
STATION/AFC
This gives rise to the f oll o
.
n t ly operating in the tuner
y drift is
n
c
is increased n times. In
z one
a powerful s t at i o n nearby on
o f f
is apt to be pulled
make it impossible
will
this problem
losing frequency response. The m1xmg is done auto­
matically by this circuit, in two stages:
below 60dBJ,L and below 40dBJ,L. Naturally, the stronger
the blend effect, the less stereo separation is
(Separation
40dBJ.t
FETI
lOOK
of E is fed to FET2 and FET3 gates. In addition,
the left channel aud i o signal is fed from
E
the FET2
and
(6) effect in both stages
When the strength of th e received signal is
b.
FET1
60dBJ,L but over 40dBJ,L,
potential at point
at points
the blend effect is a v ai
When the strength of the received signal is
is
c.
60dBJ.L Tr1 is almost switched on, wh i ch
is
condition as that described
cels the blend effect.
,
the AFC g o e s off automatically wh
is touched.
2. More
w recent
ing
function alt ogether, de p en di ng
techno l ogy to su p p r
/ n ,
1 are designed t o resist the affect of t em p e r a t
tuations, so that drift can be f orgotten as a se riou s
r o b l e m .
p
e v e n
, In such a tuner, the a d d i t i o
v
pro ide extra protection aga in s t
the su pe ri or feature of the Yamaha system.
1 KH
z BdB, 60dBJ.t
=
Lt o--_,.- -. .. .. .,.- -- --4- --<> L o
R1
FET3 gates for a steady
and
.
Tr 1 i mpedance lowers and
(i)
is enough to cause the potential
@ (£)
to drop, below -0.5V, so that
and
ab l e but only via
l ,
in a
( 1)
n the tuning
e
tuners tend to do away with the AFC
upon advanced circuit
e drift. In these t u n er s
ss
n of A F
C
drift - and thi s
for signals
available.
1 KHz=
14dB)
Ro
AUDIO SIGNAL LINE
Fig. 2
to
FET1
blend
e low
b
FET3.
over
t h e same
is
e This can­
b o v
.
knob
circuits
,
u r e fluc­
will of course
is