The Marantz
Model 125 is an all solid state AM/FM streophonic tuner incorporating the
advanced innovative design and unparalleled technology that have made marantz
famous in the audio component industry. The Model 125 features a highly
selective AM tuner, a superb Dual Gate MOSFET FM front end, a phase locked loop
stereo multiplex demodulator, variable muting and output level controls, linear
phase IF LC filters, provisions for the connection of a four channel adaptor,
and a front panel selectable de-emphasis network for Dolbyized FM broadcasts.
The Model
125 is equipped with two meters, a Signal Strength Meter and an FM Tuning
Meter. The Signal Strength Meter indicates the signal strength of any AM or FM
broadcast. The FM Tuning Meter operates only when FM is selected and indicates
correct station tuning.
The FM tuner
section of the Model 125 is equipped with electronically triggered circuits
which automaticaally mute interstation noise and automatically switch to the
proper mode of operation for stereo and monophonic FM broadcasts. In addition,
the Stereo indicator light automatically indicates a stereo broadcast when the
Mono pushswitch on the front panel is in its normal out position.
Output Level
Control
This control
attenuates the level of both stereo output channels to match the line level of
other components in the system.
Muting Level
Control
This switch
controls the muting circuit to eliminate interstation noise. Three muting
threshold levels can be selected, each activating muting at a different signal
strength. Low (5 µV), Med. 920 µV) or High (100 µV). If desired, the muting
circuit may be defeated by placing the switch in the Off position. This
prevents the tuner from muting very weak stations along with the noise.
Hi Blend
Function
The Hi Blend
functionis useful for quieting weak stereo FM signals with excessive noise
and/or interference. When activated, the Hi Blend slightly reduces separation
at high audio frequencies. This offers moderate separation along with moderate
suppression of out-of-phase noise and distortion components. Unlike most noise
filters, the Hi Blend does not sacrifice full frequency response.
Technical
Description
Front End
FM antenna
signals are applied through a balun transformer and an Antenna Attenuator
switch to the antenna coil which drives a Dual Gate MOSFET RF amplifier.
Antenna
Attenuator "Out" - the attenuator circuit is cut off and the FM
signals are directly fed to the FM antenna coil.
Antenna
Attenuator "In" - the signals are attenuated approx. 20 dB by the
attenuator network, then fed to the antenna coil.
A five
section tuning capacitor tunes antenna, interstage and oscillator circuits
which provide exceptional selectivity and spurious signal rejection. The signal
from the RF amplifier are fed through the triple tuned Butterworth type RF tank
circuit to the Dual Gate MOSFET Mixer stage, which is also fed by the signal
generated by the local oscillator. This mixer converts the carrier frequency to
the 10,7 MHz intermediate frequency. Careful attention to the thermal and
electrical characteristics of the local oscillator has minimized drift, thus
eliminating the necessity for AFC. The 10,7 MHz converted signal is then fed to
four linear phase IF LC filters which include and are followed by five stages
of limiting. It is then, in turn, processed through the FM discriminator. The
output of the FM discriminator is fed to a buffer amplifier which then drives
the stereo multiplex demodulator.
IF Stages
The IF
sectionconsist of five transistors with four stages of IF LC filters (one
6-pole filter and three 4-pole filters. The characteristics of these filters
are ideal in that the 200 kHz passband is phase linear, with sharp cut-off
slopes. Its exceptional phase linearity assures the elimination of a major
source of high frequency distortion and a loss of stereo separation. The sharp
cut-off slope provides outstanding selectivity, permitting reception of closely
spaced channels.
Limiters
The Model
125 utilizes five multi-staged IC limiter amplifiers, eliminating the need for
an IF AGC circuit which introduces low frequency distortion. Undesirable
Amplitude Modulation (AM signals, AM nise, AM distortion) are removed from the
IF signal by the limiters.
FM
Stereo Demodulator
The stereo
composite signal obtained from the buffer amplifier is fed to the phase locked
loop stereo demodulator IC circuit and decoded into both left and right channel
signals. Each left and right channel signal, is then applified to the 19 kHz
and 38 kHz filters and de-emphasis networks, to remove the undesired switching
carrier signal in the audio signals. Next, each audio signal is applied to the
IC, which includes such functions as audio signal amplifier and muting circuit
and is amplified to the required signal level of about 1 volt RMS. Finally,
each amplified signal is fed to the FM switch. The phase locked loop iC is
equipped with a separate automatic Stereo/Monaural switching circuit. The
circuit examines the input signal intensity and activates the stereo
demodulator circuit and the stereo indicator lamp automatically when the input
signal is strong enough to provide quality stereo reception. When the input signal strength is below the
threshold level, the FM stereo broadcast is processed as a monarual signal.
Improved signal-to-noise ratio is obtained in the Mono mode during low signal
levels.
Muting
Circuit
In the
absence of an FM carrier, all FM receivers inherently produce interstation
noise. The muting circuit eliminates this noise, providing noise-free tuning
from station to station. A muting circuit consisting of a two transistor noise
amplifier and an IC has been incorporated in the Model 125. the muting circuit
perfectly mutes out all the interstation noise and also completely mutes out
the side slope spurious response of the unit. The circuit has been designed to
minimize annoying switching noise as the tuning band is scanned.
AM Tuner
The AM tuner
section is composed of one IC and three
transistors. One of them is a signal strength indication amplifier,
while the other two are used for amplifying detected audio signals. A three
section variable capacitor is used to insert two tuned circuits into the RF
stage for high selectivity and improved spurious signal rejection performance.
The ceramic filters utilized in the AM IF amplifier are designed for higher
selectivity and wider bandwidth for interference-free high quality AM
reception.following the AM IF amplifier, the AM detector recovers the audio
modulation and presents this signal to the mode selection switch. The AM tuner
and IF amplifier are subjected to the action of an effective automatic gain
control circuit which maintains a constant signal level for all stations in the
AM band.
Specifications
FM Section
Quieting
Slope: 1,7 µV for 30 dB, 5 µV for 57 dB,
10 µV for 62 dB, 50 µV for 70 dB
Ultimate
Quieting: 50 µV for 70 dB
Selectivity: alternate channel, better than 85 dB
Capture
Ratio: better than 1,5 dB
Stereo
Separation: 40 dB at 1 kHz, 27 dB at 15
kHz
Total
Harmonic Distortion:
Stereo
: less than 0,3%
Mono : less than 0,2%
Frequency
Response: 30 Hz to 15 kHz ±1 dB
Total
Spurious Rejection: better than 100 dB
Image
rejection: better than 100 dB
AM
Suppression: better than 60 dB
IF
rejection: better than 100 dB
Antenna
Impedance: 300 Ω (balanced), 75 Ω
(unbalanced)
Quadradial
Output: 300 mV, 15 K Ω for ±75 kHz Dev.
AM Section
Am
Sensitivity: better than 40 µV
Selectivity: Adjacent channel, 1000 kHz, better than 30 dB
AM
Bandwidth: 7 kHz (-6 dB)
Image
Rejection: better than 70 dB (14000 kHz)
General
Power
Requirements: 220 V, 50/60 Hz
Power
Consumption: 25 watts
Dimensions (
W x H x D): 15-3/8" x 5-3/4" x
11-7/8"
Weight
[net/shipping]: 17,2 lbs/ 23,8 lbs
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