Pioneer SX-3800 manual O W E R N D I C a T O RC I R C U I T, Fig .4 12 Power indicatorcircuit

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4 . 7 P O W E R] N D I C A T O RC I R C U I T

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Fig .4 - 12 Power indicatorcircuit

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The SX-3800 output power indicators feature fluorescentindicator tube (FL tube). In this tube, thermionic emissions from the cathode are ac- celerated into the fluorescent substance of the segmentalanodes,resulting in the emissionof light. This tube is used to indicate numerals,letters,and other symbols.

An outline of the FL tube drive circuit is shown in Fig. 4-12. The output circuit sj"tnalis appliedto pin no.6 ( ) of the IC (TA?318f-A).The IC con- tains a detector circuit, conpressor (40d8), and peak hold circuit for both left and right channels.

The dynamic range of the signalis thus contracted by 40dB to obtain a "peak held" DC voltage.

The output pou'erindicator segmentsof tire FL tube are driven by the HA12010 ICs (one for each channel) equipped rvith 12 pairs of differential amplifiers. Theseamplifiers are biasedat increasing levels,so each amplifier lvill commenceto operate separatelyas the input level increasesAnd. since these amplifiers apply the voltages to the output power indicator segmetrts,each successivesegment will light up in turn as the input level rises.

4 . 8 P R O T E C T I O NC I R C U I T

The purpose of this circuit is to protect the speakersand the power amplifiers.The relay in the output circuit is automatically opened in any of

the following cases:

L. During the "transient operations" lvhen the power supply is turned on and off.

2.Upon detection of an overload, causedby a short circuit in the ioad.

3.Upon detection of a DC voltagein the output causedby componentfailure or accident.

MutingOperationwhen PowerSupply is Turned On and Off

With reference to Fig. 4-13 when the porver supply is turned on, Q3 turns off due to *81 (l'he time constant of the *81 circuit is very sma11.). If thereis no input (DC) on Qb and Q6, they will be off, and the timing capacitor C1 chargesup through R8 and R6, and thus Q4 turns on. \Vhen Q4 condr,rcts,tire relay operates,and the output muting on the power amplifier will be removed.

When the polver supply is turned off, -81rvill abruptly decay,and Q3 will conduct owing to the resiclualcomponent of +81. As a result, C1 rvill rapidly discharge,Q4 will ceaseto conduct, rvhere- upon the relay will become de-energizedand restoremnting.

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Contents Sefvice nual FM Ouartz Locked SixSTEREORECEIVER-gaooContents H H T H HFM TunerSection P E C T F T C a T I O N STo 20000Hertzt02dB Or, iori ,ro i ,ou OdBMiscellaneous Eix-3El00ISemiconductors FurnishedPartsGnlcHrNEss @sELEcroR Tront PanelfacilitiesSpERrERswtrcHEs @ bunnrz LocKEDtNDtcAToR@ volunnEcoNTRoL GRl-Rr\cE @coNTRoL@f--q-*@ Block Diagram1l , or LhTjl 68-llFig 1 Choppertype switchingcircuit Switchins,is.rc-1q/ t h LCompositesignal CircuitdescriptionsSx-gaoo Mode Fig 5 Blockdiagramof PD5009G 6 D 1 D 5 t i m e d i v i s i o np u l s es i g n a l s B l e1Signal lndicatorCircuit Fig .4 7 SIGNALindicatordrivecircuitFig 9 Poweramplifier More,becanselhere is no time clonstantin the NFB Excellent high frequency characteristicscomparaBle lo those of a small-signaltransistor.Further Circuit ir-rthe lorv-frecluencyregion, amplificationFig .4 12 Power indicatorcircuit O W E R N D I C a T O RC I R C U I TOverloadDetector Deenergized, thus causing the output circuit toBecome de-energized,thus causing the ourpur Overload detector circuit incorporatesDisassembly Front panel Bonnet case Bottom plateRearPanel Parts LocattonFront View with PanelRemoved AKE.O54Ia.i TUNERAssy GWE-133+I t i t Rrprro&ffi$ll1rl + +D16l IlIlLiTtFTTTTTTT- - 1 * l l l l t t INDICATORAssy AWV-OO9E0UALIZERAssy AWM-227 Rtrf TiiI t TONECONTROLAssy# x r , o E i t t l i 6 YTttt,,.,i%hi*i*U 8lr rorAL2oowMAx AI I h-l# *n LmfiiOl!6 - j,r-l*-,,-s-l = # . = - r?tA tlDzrT 4u- @ *ronce 3lilli Nffi$r-ffir FfTJ-ir S5flsIFuse64 BottomViewTop View GWEDial pointer I a L C O R D S T R I N G I N GN i n gd r u m Dialshaft Startingpoint Dialpointer GK 6 AdjustmentsArrrrTl To FM300n ANT terminals MPXsignalgeneratorConnectSIGNALmeteror DC voltmeter AC voltmeter Distortionmeter R E Ct e r m i n a lTo AM ANT 1kfl resistor TerminalFis .8 R a n t e n n ac o i l AM signalgeneratorAC voltmeter To RECterminal LvR5ll AFosc,lt ,-d + u tFJaJtuL6 \ ,v\ Te ,t . 1Fig .8 FL indicatorassemblyVR2*€ @vnr PD5009AAB.24O ExteriorComponentsVBZ3OPOSOFMC AcN lrs Interior ComponentsRo. AEK-rog 25 e6Ae*-\ 228? T SX.SClOl Fr-r rHeat Sink Block H 1 3Usr Illl\N n n n t E6nmr TunerAssemblyGWEAN,,4Sa NrrezZS3,s4 PrecautionsC65,C66,C70,C71 c63,C64 C303,c304 Arc-o72SwitchAssemblyGWS-226 ToneControlAssemblyt G W G 1 4AWS-146 SwitchAssembly Lynlgt9 9*ie9Ncru-rat PowerAmplifierAssemblyGWH-139Nr21, R12z PowerSupplyAssemblyGWR-j22 9yqlglt o*lelglSwitchAssemblytGWS-223 FL IndicatorAssemblyAWV-009SpeakersTerminalAssemblytGWS-222 AR8-355 A C K I N GADH AHD 7s5FM Ouartz Locked StereoreceiverP E C F I C a T I O N S With exceptionof thissupplements$ r u r Contrastof Miscellaneous PartsSrs Rd.*dr q l SCHEMATICDIAGRAM,P.C. Board PatternsandIBi ihl*cr Parts List Il,*3Lr-l--.q.iliffi 3il3i!11UJl--J RtmlSX-3EtCO/si/GirS 11ffiflCl, c2 €tX-ggtOO/gi/GlrsAWS-148 C3,c4

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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