What is stereo?

There are now two system of high fidelity, monophonic (monaural) and stereophonic. Monophonic is a system that starts from one microphone and is fed through a single high fidelity set. Stereophonic is a double system. Two separate microphones are placed at different sides of the orchestra and two different systems are used to keep the two signals or channels separated. Two separate speakers are used, placed on different sides of you room. Stereo is much like 3-D photography, two slightly different sound reach your ears giving you a new dimension in sound.

H.H. Scott '59

Sharp Optonica ST-3636

Optonica ST-3636 features:
FM IF AMP. Section
FM Front-End Circuit
FM IF  Band with Selector Circuit
FM Tuning Auto-Lock Circuit
FM Detection Sections (Quadrature Detector Circuit)
Hi-Blend Circuit
Low-Frequency Amplifier Circuit
Power Supply Circuit
Audio Muting Circuit

FM Detector Circuit. This unit employs "Quadrature Detector" based on newly developed IC, which is substituted for ratio detector and Foster-Seeley's detector that have been sp far used. The basic structure of quadrature detector circuit is as shon.

Multipath Detection Circuit
Multipath Distortion. In any of electric-wave signals broadcasting including FM waves, it would be ideal if the signals emitted by abroadcasting station were caught by a receiver's antenne as they midway. Actually saying, however, there are practically some obtacles (like mountains and  skyscrapers, etc.) between the transniter side and the receiver side, which have the emitted signals undergo a phenomenon of waves reflection, leading to that the signals become distored variously when caughtby the receiver's antenna
A simple exampleconcering this distortion is that in the mountainous area or large cities full of higher buildings, the TV stes get produced images be doubled (this called a ghost). This phenomenon is a sort of multipath distortion and it is caused by the there is a time delay betweenthe direct waves and reflected waves. In the case of radio sets, this is reffed to as that the reproduced sounds contain distortions; particularlyas for stereo broadcasting signals, since their band width is rather wider and so they are apt to be interferred by various objects, not only the distorted sounds are produced but also the stereo separation characteristics will suffer. These phenomena are named a multipath distortion.

Multipath Distortion Detection. Multipath distortion are classified into the two, that is, phase distortion which is found out by the frequency discriminator and AM distortion which is removed by the limiter circuit; the latter AM distortion is actually subject to detection by the multipath detector circuit.

FM Stereo Demodulator Section
Features of PLL Stereo demodulator Circuit.
This set incorporates a stereo demodulator circuit that comprises ICs with the PLL (Phase Locked Loop) system applied. The PLL FM demodulator circuit is provided with such characteristics as mentioned  below.
In order to demodulate stereo composite signals, it is necessary to take a 19 kHz pilot signal out of the stereo composite signals and to make it a 38 kHz signal.  Most of the conventional methods to obtain such a 38 kHz signal are frequency doubling ones which utilize a nonlinearity of the elements. Compared with the conventional type, the recently developed IC-ed demodulator provides more sufficient separation effects.  However, since it also requires 2 or 3 coils like the conventional one, if even one of them is dislocated from the initially adjusted point due to a secular change the separation effects will be deteriorated. Moreover there is such a contradiction that the more the efficiencies of the coils are increased enough to withstand the outer pulse signals like automobil ignition noises, the more the coils suffer secular changes.
To eliminate such disadvantages as above, PLL system is employed in the method to make a 38 kHz signal using a 19 kHz pilot signal.

Variable Air Check Calibrator Circuit
Theis circuit is to make appropriate the recording level in advance when recording FM broadcast into the tape deck or equivalent.
The circuit  is reffered to as this variable air check calibratoe circuit and it is composed of an air check oscillator circuit, air check meter indication circuit and further a circuit by which, when the air check/muting switch is set to 'air check on' position during FM reception, the indication mode of the signal/air check meter will be changed from 'signal level' to 'air check level' indication.

FM Section
Tuning Range:  87,6 -108 MHz
IF:  10,7 MHz
Sensitivity (at SN 26 dB, 40 kHz deviation):  1,4 µV
Frequency Response:  30 - 15,000 Hz +1,5 -3 dB
Image Rejection:  110 dB (at 98 MHz)
IF rejection:  100 dB (at 98 MHz)
Selectivity [normal/wide]:  72 dB / 30 dB
Capture Ratio [normal/wide]:  2,5 dB / 1,5 dB
AM Suppression:  45 dB
Signal-to-Noise Ratio:  65 dB (40 Hz deviation)
Distortion [normal/wide]
Mono :  0,6% / 0,25%
Stereo:  0,8% / 0,4%
Stereo Separation:  42 dB (1 kHz)
AM Section
Tuning Range:  520 - 1620 kHz
IF:  455 kHz
Quieting Sensitivity:  400 µV/m
Image Rejection:  55 dB (at 1400 kHz)
IF Rejection:  50 dB (at 600 kHz)
Distortion:  1,5%
Audio Section
FM Output Voltage
Variable : 0 - 0,55 V
Fixed :  0,35V
AM Output Voltage:
Variable :  0 - 0,35 V
Fixeed :  0,2 V
Circuit:  Superheterodyne system, 2-band with PLL stereo demodulator
Featured:  FM muting, FM multipath detection, variable air check calibrator, FM auto lock, FM IF band selector circuit
Semiconductors:  28 Transistor, 36 Diode (1-zener diode); 4 ICs, 3 FET (dual gate, MOS type); 3 LED
Power Source:  AC 110/220/240V, 50/60 Hz
Power Consumption:  24 W
Dimensions (W x H x D):  442 x 144 x 373 mm
Weight:  7,5 kg

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