Marantz SD9000 - Circuitdescription; Playback Equalizer Circuit; Recording Currentsetting Circuit

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).
1. R352 is used for precisely adjusting the motor speed
to 3,600 rpm.
2. 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) Reproduced frequency (Hz)
1800 3000
[ 3600 6000
POO3 P206
20 R325 R326
RED YEL io} 1]
Sern
(00)
vec
TO}
[OT
Ss0s-1283-34
07
e& 1; 1% ol-ve} | 3-3/4
(HI! SPEED ADJ.)
MOTOR SPEED ADJ.
3.2 PLAYBACK EQUALIZER CIRCUIT
The playback equalizer circuit is shown below.
@ PB LEVEL Adu.
1-7/8 IPS
R30!
Veo
$305
S30I:TAPE SELECTOR SWITCH 3-3/4 IPS
(NORMAL)
$305= SPEED SELECTOR SWITCH S301-8
NORMAL <-> NORMAL
Time contants of the playback equalizer circuit at each
tape speed and selector position are as follows:
POSITION CrO2
TAPE | 1-7/8 IPS} 120 uS 70uS | 70uS
SPEED | 3.3/4 IPs | 70 uS 35uS | 35us
TAPE ion [or SPECIAL/ | ues
Circuit Function at Each Time Constant
(1) 120 pS
$305 is Tape Speed Switch for normal position.
In the diagram, this switch is in the depressed posi-
tion, causing 0114 and Q115 to turn OFF due to
zero bias voltage. In this case, the playback time
constant is set to 120 uS by C148 and R168 ~ R170.
(2) 70 uS
When the tape speed is 1-7/8 ips (4.75 cm/sec) and
$301 is OFF (S115 turns OFF when the other tape
selector switch is depressed), a bias voltage is applied
to the base of Q115 which is then turned ON. When
the tape speed is 3-3/4 ips and $301 is ON, Q115
is also ON. In either case, the playback time constant
is set to 70 pS by C148, R168 ~ R170, C152 and
R174.
(3) 35 pS
When the tape speed is 3-3/4 ips (9.5 cm/sec) and
$301 is OFF, Q114 is ON and the playback time
constant is set to 35 uS by C148, R168 ~ R170,
C150 and R172.
3.3 RECORDING CURRENT SETTING CIRCUIT
Recording currents at each tape speed and each position
of the tape selector switch are determined by the follow-
ing circuit:
$304-1
S305-| RH?
$302-1
RIB
FOR DOLBY NR
To RECORD AMP
$301: Tape selector switch — Normal
$302: Tape selector switch — Special/CrO2
$304: Tape selector switch — Metal
$305: Tape speed switch
The switch (S303) for the FeCr position is not included in
the above circuit. The recording current at this position
is determined by R121 and R124 or R122 and R123.
The resistors used to determine recording current at each
tape speed and each tape selector switch position are shown
in the table below.
TAPE SELECTOR
NORMAL | SPECIAL! | coc, | METAL
CrO2
POSITION
R121, R119/R121, R117 | R121
TAPE | +78 1s R124 R124 R124 | 124
SPEED
[29741 ie a R922, || a5
R123
R123 Ri23