JVC MF-47L - Specification; New Technical Information; FM Pre-Set Tuning Circuit

Specification
Cassette deck
Type
Track system
Bias & Erase
Heads
Frequency response :
Wow and flutter
S/N ratio
Tuner
Type
Tuning range
FM Preset
Stereo cassette deck with Auto-stop
and Dolby Noise Reduction system
4-track, 2-channel stereo
AC bias and AC erase (Bias
Frequency 57kHz)
Permalloy head for Record/Play
Ferrite head for erase
(Normal) 30—13,000Hz
(Chrome) 30—15,000Hz
0.15% (WRMS)
50dB
The S/N is improved by 5dB at
1kHz and 10dB at 5kHz or more
with Dolby NR system
3-band (FM/MW/LW)
FM stereo tuner with PLL IC
Multiplex
FM 88—108MHz
MW 520—1600kHz
LW 150—350kHz
7 feather touch selectors
Amplifier
Type
Continuous power
MF-47L/ML
IC power amplifier with bass and
treble controls
25 watts RMS per channel at 4 ohms
(T.H.D. 1%)
20 watts RMS per channel at 8 ohms
(T.H.D. 1%)
Music power 100 watts
Turntable
Type Belt drive turntable with auto return
mechanism and cueing
Speed 33-1/3, 45 rom
Turntable 280mm
Motor DC Electronic Governer Motor
Cartridge Moving magnet type
General
Power source
Power consumption :
Dimensions
Weight
110V, 120V, 220V, 240V, 50/60Hz
175 watts
160(H) x 600(W) x 425(D)mm
12.5kg (27.4 Ibs)
1 manual selector
Sensor (8 positions)
Stereo separation 35dB
Features
DOLBY NR circuit built-in.
7-keys FM pre-set touch senser equipped
Auto-return record player & DC electrogovernor.
PLL circuit adopted in FM multiplex.
25 Watt per channel/4Q, 20 Watt/8Q
New Technical
Information
— FM pre-set tuning circuit —
The FM pre-set tuning circuit adopted in model MF-47L/ML
is composed of electronic tuner and selection circuit of
FM broadcasting station. This system features easy
selection of desired FM station merely by touching your
finger on the touch-sensor on the front panel of set.
The outline of this system is that the selection circuit
generates a voltage corresponding to desired FM station,
and makes the voltage apply to the electronic tuner to
select the station. The features of this system are:—
1. Instant selection of FM station can be made without
rotating the tuning knob.
2. Free from mechanical defacement in selecting station
because of electronic system.
However, on the contrary, the system has a demerit that
the circuit is complicated as the selection circuit is added,
etc. We should therefore like to explain about the outline
of basic circuit and function. Please utilize it as hints when
repairing.
Principle of basic circuit operation of electronic tuner
The electronic tuner operates so as to tune in desired
FM station, and makes a specified IF output apply to
IF amplifier circuit. For the frequency tuning element
of this function, the variable capacity diode (called as
varactor diode or varicap.) is used.
The variable capacity diode has a characteristic as in Fig. 1,
and in case the resonance circuit is formed by use of the
V.C. diode, its resonance frequency becomes higher
according as reverse voltage is applied to the V.C. diode.
FM pre-set circuit utilizes this principle of operation.
Capacity/Resonance
Frequency
Tuning Voltage
Fig. 1.