Scott-433-High-Fidelity-1971-10 电路图 维修手册.pdf

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1、new equipment THE CONSUMERS GUIDE TO HIGH FIDELITY EQUIPMENT reports Scotts Digital FM Tuner The Equipment: Scott 433, a stereo -FM digital tuner. Dimensions (in integral three -sided wood case): 17% by 6 by 15 inches. Price: $549.90. Manufacturer: H. H. Scott, Inc., 111 Powder Mill Rd., Maynard, Ma

2、ss. 01754. Comment: Automated, foolproof tuning-and the new front -panel look associated with it-is featured in this new model from Scott. In place of the familiar multigang tuning capacitor, dial cord, knob, and station dial, we find in the Scott 433 a digital frequency synthesizer, which can be de

3、scribed as a small computer made of integrated circuits. The set receives stations by syn- thesizing a particular FM -channel frequency (the action is regulated by a quartz crystal reference standard). It then tunes automatically to the exact center of the channel, and reads out the frequency select

4、ed on an illuminated digital indicator. In tuning the Model 433 you have four options. One is via a set of keyed program cards, of which one hundred and five (covering the one hundred FM -channel alloca- tions, plus five spares to use in making replacements should any become damaged) are supplied wi

5、th the set. Insert a card into the slot on the front panel, and the set will lock to that channel and hold it whether the channel is being used by a station or not, and regard- less of the quality of the signal. The cards, incidentally, are marked for channel frequencies, with space for you to fill

6、in the station call letters used in your locale. You also can tune the 433 by any of three scan meth- ods (with no card inserted in the slot). Note the bar -and buttons -grouping in the center of the front panel. The bar at the left is marked scan. The three buttons next to it are labeled as a group

7、 scan mode selector, and individually as channel, stereo, and station. Above this group is a slide control marked channel scan speed with slow and fast indicated at its two ends. With the channel button pushed in, you can press the scan bar and the tuner will run through the entire FM band. The spee

8、d with which it does so is regulated by the slide -control above it. The frequencies being scanned show on the digital readout indicator. When you release the scan bar the set will remain locked in on the last frequency reached. With the speed control on slow, you actually can use the scan bar to pi

9、ck your way carefully through the band, with enough time to release the bar and check the program content of any station that strikes your fancy. With the station button pressed, the set will scan the FM band automatically until it hits an acceptable FM signal (i.e., a broadcast strong enough to tur

10、n off the muting circuit and switch on the station indicator light). The scanning then stops and the set remains on that station. To move from this particular station to the next acceptable station, simply press the scan bar, and the scanning action will continue. The scanning also will resume if th

11、e incoming signal drops below minimal strength due to FM transmission vagaries. To prevent this, simply press the channel button after the scanning has brought in a station you want to hear. With the stereo button pressed, a similar scanning action occurs, but this time the set will stop scanning on

12、ly when it reaches a station strong enough to trip the automatic stereo switching circuit and cause both the REPORT POLICY Equipment reports are based on laboratory measurements and controlled listening tests. Unless otherwise noted, test data and measurements are obtained by CBS Laboratories, Stamf

13、ord. Connecticut. a division of Columbia Broadcasting System, Inc., one of the nations leading research organizations. The choice of equipment to be tested rests with the editors of HIGH FIDELITY. Manufacturers are not permitted to read reports in advance of publication, and no report, or portion th

14、ereof. may be reproduced any purpose or in any form without written per- mission of the publisher. All reports should be construed as applying to the specific samples tested; neither HIGH FIDELITY nor CBS Laboratories assumes responsibility for product performance or quality. Ot toBER 1971 41 RadioF

15、ans.CN 收音机爱 好者资料库 station and the FM stereo lights to come on. Again, you can resume scanning by pressing the scan bar, or look the set to the station by pressing the channel button. Regardless of what mode of automatic scan has been selected, and regardless of what channel any of those modes has pu

16、lled in, the insertion in the slot of a keyed program card overrides it all and returns the set to the channel keyed on that card. The station and FM stereo indicator lights, as well as the two meters (one for signal strength, the other showing multipath distor- tion) all operate in any mode of tuni

17、ng used. We found this tuning system somewhat complex at first, but also fascinating-and foolproof insofar as ac- curate, on -the -nose channel selection with minimal drift and perfect frequency calibration are concerned. Its drawback of course is that the sequence of channels runs only one way (fro

18、m the higher -frequency channels down); you cannot tune in the opposite direction as you would with a conventional tuning dial. Lets say you want to go back to 91.5 MHz after having tuned in 91.3 MHz. You must either fish out the 91.5 MHz card or let the tuner scan downward from 91.3 MHz, return to

19、the top of the band, and continue downward until it comes to 91.5 MHz. This is best done, by the way, with the channel button pressed and the speed control on fast-but watch your digital readout and go to slow scan as needed or youll zip right past the channel you want. In addition to the features d

20、escribed, the front panel contains button switches for power off /on; muting off/ on (when on, this control will mute stations not strong enough to activate the station light); mono/stereo mode; and a high -frequency filter. Theres also a tape out jack for convenient patching -in of a tape recorder;

21、 we found that this jack also will serve as a make -do stereo headphone jack for private listening, although the obvious impedance mismatch does result in fairly low volume. A second slot, under the card -insertion slot, will hold up to eight program cards (presumably those for the stations most oft

22、en tuned in), although we pr9fer to keep these cards in numerical order in the box they came in. The rear of the Scott 433 contains three stereo pairs of signal output jacks, all controlled by a pair of left- and right -channel level adjustments. Thus, any combination of up to three external stereo

23、amplifiers and/or tape recorders can be driven at once. Theres also a stereo output for driving an oscilloscope indicator, and an- other jack for feeding a composite multiplex signal from the 433s IF strip to a four -channel broadcast decoder, should one ever be needed. Even if this jack is used, by

24、 the way, the normal two -channel stereo audio is still available at the signal -output jacks. A special test jack also is provided for professional use. Antenna options include terminals for regular 300 -ohm twin -lead, plus a grounding screw for use with shielded twin -lead. Theres also a receptac

25、le for a 75 -ohm input jack, and a switch that selects between 300 ohms and 75 ohms for the antenna input impedance. A fuse holder, an un- switched AC convenience outlet, and the sets power cord complete the rear picture. Its novel tuning arrangement aside, the Scott 433 offers excellent FM performa

26、nce. Sensitivity was meas- ured at CBS Labs as 2.1 microvolts. The FM sensitivity curve descends steeply and reaches maximum quieting of 48 dB for 100 microvolts of input signal, with no signs of front-end overload at higher input signals. In our cable -FM test we logged 52 stations of which 40 were

27、 judged suitable for critical listening or off -the -air taping. Our tests also indicate that this set has excep- tionally good selectivity (which prevents strong signals from swamping their weaker neighbors), and this char- acteristic permits stations to come in more clearly than they otherwise wou

28、ld on an FM set (even one with higher numerical sensitivity) that had poorer selectivity. The tuners capture ratio at 2 dB is excellent, as is its signal-to-noise figure of 62.5 dB. Multiplex carrier sup- pression (see data) is exceptionally good; IM and har- monic distortion, very low. Audio respon

29、se, in mono and stereo, is linear within the normal broadcast audio spectrum of 50 to 15,000 Hz; channel separation for stereo signals is outstanding. The sound of the Scott 433 is eminently clean and honest. For the perfectionist who can afford it, the Scott 433 offers FM performance of top quality

30、 combined with state-of-the-art operational options. +5 0 -5 +5 co0 -5 -10 c, -15 cal) -20 -25 - 30 -35 - 40 CIRCLE 143 ON READER -SERVICE CARD MONO FM RESPONSE +0.5, -4.5 dB, 20 Hz to 15 kHz STEREO FM RESPONSE - Left channel: +0.5, -5 dB, 20 Hz to 15 kHz - Right channel: +1.5, -5 dB, 20 Hz to 15 kH

31、z CHANNEL SEPARATION - Left channel 40 dB, 150 Hz to 2.5 kHz; 20 dB, 20 Hz to 12.5 kHz - Right channel 40 dB, 130 Hz to 2.5 kHz; 20 dB, 20 Hz to 12.5 kHz 2050100200500 1K2K5K10K20K FREQUENCY IN HZ -10 co c -20 zz c -30 x cc -40 00 IHF FM SENSITIVITY 1.9- 2.2 11 at 90 MHz 1.9 V at 98MHz 1.9 V at 106

32、MHz 50 1101001K RF INPUT IN MICROVOLTS Scott 433 TunerAdditional Data 10K100K Capture ratio S/N ratio IM distortion 2 dB 62.5 dB 0.30% THDMonoL chR ch 80 Hz0 38%0.80%0.82% 1 kHz0 39%0.54%0.58% 10 kHz0 40%1.60%1.40% 19 -kHz pilot 38 -kHz subcarrier -66 dB -68 dB 42HIGH FIDELITY MAGAZINE RadioFans.CN 收音机爱 好者资料库