Marantz SD1000 - Circuit Description; Tape Speed Selector Operation; Playback Time Constant Explained; Recording Compensation Methods

3. CIRCUIT DESCRIPTION
3.1 TAPESPEED SELECTOR (U, C, A version only)
Tape speed is changed by switching the motor speed to
1,800 rpm for 1-7/8 ips or to 3,600 rpm for 3-3/4 ips.
In fast-forward or rewind operation, however, the motor
always rotates at 1,800 rpm.
NOTE: The N version is not equipped with the tape
speed selector. The motor and motor pulley used
in the N version are different from those used for
the U, C, A version.
1. As shown in the figure below, the motor rotates at
1,800 rpm when R945 (5k) 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) Reproduced frequency (Hz)
1800 3000
3600 6000
YE
O
1-7/8 ips
$305
3.2 PLAYBACK TIME CONSTANT
The reason why the playback equalizer time constant is
switched is so that any type of tape can have optimum
performance at any of the two available tape speeds.
TAPE SPEED | TAPE SELECTOR | TIME CONSTANT
POSITION (usec)
NORMAL 120
SPECIAL/FeCr 70
NORMAL 70
SPECIAL/FeCr 35
The time constant is selected between 35, 70 and 120 us
using a transistor switching circuit.
PB LEVEL
ADJ.
TO DOLBY
iciaso1)
{
1
'
I
1
1
L
107 t
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t
J
3-3/4 IPS
$301 og 8308
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1-3/4 1S
$301: EQ SWITCHIN: NORMAL, C: SPECIAL/FeCr)
S308: SPEED SELECTOR SWITCH
3.3 RECORDING COMPENSATION
The method of recording compensation is the same as
that used in our existing units where the amount of feed-
back in the recording amplifier (Q902) is varied.
TAPE SPEED | TAPE SELECTOR
(IPS) POSITION
1-7/8 NORMAL
COMPENSATION
Peaking by L102, R146,
and C127 only.
Mid range compensation by
double time constant circuit
of R143 and C124 and
R142 and C123.
SPECIAL/CrO2 Mid range compensation by
Q109 turned on by R144
and C125.
NORMAL Peaking by L101, R148, and
C129 only.
FeCr
Mid
range
compensation
by
R140, C122, R139, and
C121 as Q110 is turned on.
1-7/8 FeCr
c128
— 7
129
| ee
R47 R148
$301
L101
$301: EQ SWITCH
$302: BIAS SWITCH
$305: SPEED SELECTOR SWITCH
ALL SWITCHES ARE IN NORMAL POSITION.
3.4 RECORDING CURRENT
1. The recording current at a tape speed of 3-3/4 ips is
smaller than that at 1-7/8 ips.
2.
The
recording
current
is
varied
by
changing
the
resist-
ance
connected
in
series
to
the
head
according
to the
combination
of
the
type
of
tape
and
the
tape
speed.
SPECIAL/
NORMAL CrO,
R135 | RESISTOR
R136 _ CONNECTED
52 64
RECORDING
CURRENT
49 60 (uA)
~] BIAS CUR-
4-7/8, 3-3/4 RENT WA)
1-7/8 PS,
1-7/8 19S
R c R138
To DOLBY
AWN
1c 501
s302 ON |s301 OF
R136 33/4 IPS
RI3B 4.7/8 1S
TO REC AMP
as02
i/) ae p-O $308
R135
$301.
EQ
SWITCH
”
$902: BIAS SWITCH
5305: SPEED SELECTOR SWITCH
ALL SWITCHES ARE iN NORMAL POSITION.