Marantz SD4000 - Circuit Descriptions

3.
CIRCUIT
DESCRIPTION
3.1
TAPE
SPEED
SELECTOR
Tape
speed
is
changed
by
switching
the
motor
speed
to
1,800
rpm
for
1-7/8
ips
(4.75
cm/sec)
or
to
3,600
rpm
for
3-3/4
ips
(9.5
cm/sec).
In
fast-forward
or
rewind
opera-
tion,
however,
the
motor
always
rotates
at
1,800
rpm.
1.
As
shown
in
the
figure
below,
the
motor
rotates
at
1,800
rpm
when
R310
(5
kQ)
is
shorted
by
S305
(speed
selector)
or
SO90
(FF/REW).
2.
When R945
is
not
shorted,
the
motor
rotates
at
3,600
rpm.
3.
R945
is
used
for
precisely
adjusting
the
motor
speed
to
3,600
rpm.
'
4.
To
precisely
adjust
the
motor
speed
to
1,800
rpm,
turn
the
variable
resistor
built-in
the
motor.
NOTE: The motor speed is known by playing back the
test tape MTT-111 and measuring the reproduced
frequency.
Motor speed (rpm)
1800
YEL
Reproduced frequency (Hz)
6000
1-7/8 ips
$301
3.2 PLAYBACK EQUALIZER CIRCUIT
A
block
diagram
of
the
playback
equalizer
circuit
is
shown below.
PB LEVEL
ADJ
i]
TO DOLBY
1¢ (A501)
163
0.012 uF
’
'
'
I
’
t
if
1
|
1
1
1
i
4
4
{
L-~-354s---4
$301: TAPE SPEED SWITCH
$302: TAPE SELECTOR SWITCH (NORMAL)
Time constants of the playback equalizer circuit at each
tape
speed
and
selector
position
are
as
follows:
Tape |1-7/8IPS| 120 uS 70 us 70 uS
SPEED [3.3/4 IPS 35uS | 35uS
Circuit Function at Each Time Constant
(1) 120uS
S302 is Tape Selector Switch for normal position.
In the diagram, this switch is in the depressed posi-
tion, causing Q153 and Q154 to turn OFF due to
zero bias voltage. In this case, the playback time
constant is set to 120uS by C157 and R158~R160.
SPECIAL/
CrO2
TAPE SELECTOR
POSITION
NORMAL
(2) 70uS
When the tape speed is 1-7/8 ips (4.75 cm/sec) and
$302 is OFF (S302 turns OFF when the other tape
selector switch is depressed), a bias voltage is applied
to the base of Q153 which is then turned ON. When
the tape speed is 3-3/4 ips and $302 is ON, Q153
is also ON. In either case, the playback time constant
is set to 70uS by C157, R158~R160, C161 and R163.
(3) 35uS
When the tape speed is 3-3/4 ips (9.5 cm/sec) and
$302 is OFF, Q154 is ON and the playback time
constant is set to 35uS by C157, R158~R160,
C163, C164 and R165.
3.3 RECORDING COMPENSATING CIRCUIT
(Tape Speed: 3-3/4 ips)
4108 1928 S60 2 1926
cros
0.0027 uF
FROM
aso3
ig |
I
1
P wo
Re
Ss
oe
°
$301: TAPE SPEED (3.3/4 IPS}
S302: TAPE SELECTOR (NOAMAL) Jo de p= Joos dss foo $302
$303: TAPE SELECTOR (SPECIAL/CrO2) ’ J d d ” u q
a
$304: TAPE SELECTOR (FeCr
$305: TAPE SELECTOR (METAL)
In the circuit diagram, C108 and R115 are used for high
range compensation, and R116 and C109 for low range
compensation. The compensating circuit for 1-7/8 ips
(4.75 cm/sec) tape speed is not shown in the diagram.
L102, R133~R136 and C123~C126 form a peeking
circuit. Peeking frequency and the amount of compensa-
tion are selected by the tape selector switch.
R130~R132 and C120~C122 are used for medium range
compensation. The amount of compensation is selected
by the tape selector switch (not available at “Normal”
position).
3.4 RECORDING CURRENT SETTING CIRCUIT
Recording currents at each tape speed and each position
of the tape selector switch are obtained from the follow-
ing circuit:
ON
R105 02
FROM DOLBY
ic (Q501)
R106 150 2
R107 1k2Q
AI1 20kN
R108 1kQ
R109 18k
A110 4.3«Q
+O
TOREC
= ASMP (Q103)
‘
: : {
t
t
(
'
!
S301: TAPE SPEED (1-7/8 195)
$302: TAPE SELECTOR (Non MAL)
5303: TAPE SELECTOR (SPC IAL/CI03)
$305: TAPE SELECTOR (mir AL)
The switch (S304) for the FeCr position is not in cluded
in the above circuit. The recording current at this pasition
is determined by R109 and R111 or R110 an¢ R112,
The resistors used to determine recording current at each
tape speed and each tape selector switch posijjon are