4 . CIRCUITDESCRIPTIONS

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4 . 1 F M T U N E R Front End

The FM front end of SX-3800 includes a 3 ganged tuning capacitor, a dual-gate MOS FET- equipped L-stage RF amplifier, and a modified Clapp circuit local oscillator. This oscillator is a voltage controled oscillator employing a vari-cap

(variablecapacitancediode). When the quartz-lock system (refer to "Quartz-locksystem") is not in

operation, a constant voltage is applied to the diode.

lF Amplifier and Detector

These employ 3 ICs and 3 dual-elementceramic filten. The IC (HA1201) of the first 2 stagecon- stitutes a single-stagedifferential amplifier current- limiting limiter. The IC (PA3007-A) in the third stage,an improvement on the former IF systemIC (PA3001-A), includes an IF limiter amplifier, quadrature detector, meter drive, and other cir- cuits. Performance in terms of distortion, S/N ratio, delay characteristics,and other parameters, shows a marked improvement in comparison to the PA3001-4.

Multiplex Decoder

The recently developed multiplex decoder IC (PA4006-A) combinesMPX decodingwith muting functions in a single IC, thereby handling the functions of the more conventional MPX IC (PA1-001-A)and AF MUTING IC (PA1002-A).

Distortion ratings and SIN ratio have been further improved by incorporating a chopper type MPX decoder. The chopper type switching circuit (see Fig. 4-1) operates by switching the signal either to ground or to the through circuit, thereby eliminating the generation of unwanted noise or distortion. Furthermore, since the PA4006-A fea- tures DC direct-coupled switching with the detec-

tor, there is no deterioration in separationat the low frequency end.

Besidesthe decoder and muting circuits, the PA4006-A alsoincorporatesthe pilot signalcancel- ler, stereo auto selector, VCO killer circuit, ivluT amplifier, and MUT control circuit.

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Fig . 4 - 1 Choppertype switchingcircuit

ouartz-Lock system

The quartz-locksystemfeaturedin the SX-3800 stereo receiver is a frequency servocontrol system employinga crystalresonator.Any displacementin the intermediatefrequency (iF) is detected asa DC voltage by the discriminator (equipped with a crystal resonator), resulting in the local oscillator frequency being corrected and subsequently locked. This extremely stable frequency servo- control systemthus ensuresthat tuned frequencies remain tuned securelyfor aslong asrequired.

When the IF signalappearsat pin no.l? of the IF system IC (PA300?-A), it is amplified and applied to crystal detector (see Fig. 4'2)which consistsof diodesconnectedin parallelin a series resonancecircuit equipped with a crystal resona- tor. The resonancefrequency is the sameasthe IF frequency(10.?MHz), which meansthe impedance at this time will be minimal, resulting in the output beingreducedto a minimum level.If the input fre- quency increases,the reactanceof the capacitance

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Pioneer SX-3800 Circuitdescriptions, InOutOutput, Switchins,is.rc-1q/ t h L, Compositesignal, Choppertype switchingcircuit
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SX-3800 specifications

The Pioneer SX-3800 is a classic stereo receiver that emerged in the late 1970s, embodying the high-fidelity audio aspirations of its time. As part of Pioneer’s widely respected SX series, the SX-3800 is hailed for its exceptional sound quality, robust construction, and an array of features that cater to both audiophiles and casual listeners alike.

One of the SX-3800's standout characteristics is its power output. It delivers a solid 80 watts per channel into 8 ohms, making it capable of driving a variety of speaker systems with ease. This ensures a dynamic audio experience, with clear highs, rich midrange, and deep bass. The receiver also exhibits low total harmonic distortion (THD) ratings, which means the sound produced is clean and faithful to the original recording.

The SX-3800 is equipped with a high-quality AM/FM tuner, which is known for its excellent sensitivity and selectivity. Featuring a large analog dial, it allows users to effortlessly dial into their favorite stations while the signal strength meter helps in fine-tuning the reception. This tuner is complemented by Pioneer’s proprietary Auto-Seek tuning function, making it easier for users to find and lock onto stations.

In terms of connectivity, the SX-3800 comes with several inputs and outputs, including phono, tape, aux, and multiple speaker outputs, offering flexibility for various audio setups. Additionally, the built-in phono preamp ensures that vinyl lovers can connect their turntables with ease, preserving the rich detail and warmth that analog sources are known for.

Another technological highlight of the SX-3800 is its inclusion of a loudness control feature, which allows users to enhance the low and high frequencies at lower volume levels. This feature is particularly useful for late-night listening or in quieter environments where detail is essential but loudness is not an option.

With its solid construction, vintage aesthetics, and a beautiful wood finish, the Pioneer SX-3800 not only performs well but also adds a classic touch to any audio setup. Its blend of features, performance, and timeless design continues to make it a desirable component in the world of vintage audio equipment. Collectors and enthusiasts appreciate the SX-3800 not just for its sound quality but also for its enduring legacy in the rich history of audio technology.
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