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Erläuterungen zu diesen US-AUDIO Seiten der 1950er Jahre

Die hier stehenden amerikanischen Artikel aus 1959 (aus der US-AUDIO) sind teilweise sehr gewöhnungsbedürftig, weil sie erstens aus einer längst vergangenen Zeit stammen und zweitens, weil dort in den USA ganz "anders" gedacht wurde als bei uns in Old Germany oder in Europa.

Vergleichbar mit unseren deutschen Hifi-Magazinen etwa ab 1962 ist jedoch, daß auch diese Zeitschrift ihre Anzeigen- Kunden und -Leser (be- oder ab- ?) werben mußte. - Weiterhin sind die Dimensionen des amerikanischen Kontinents mit den unseren hier in Europa nicht vergleichbar. - Ein Redaktions-"Trip" von New York nach Los Angeles oder Chicago oder gar in die Wüste nach Las-Vegas zu einer der CES- Audio- "Shows" war - auch mit dem Flugzeug - immer noch eine Weltreise. Und jede Ausstellung oder "Messe" wurde als "Show" deklariert. Und natürlich, in USA musste alles "Show" sein, um beim Publikum einige Aufmerksamkeit zu erzeugen.


Equipment Profile - AUDIO • JANUARY, 1959

Wie bei uns auch, wurden neue Geräte recht ausführlich - selbstverständlich mit sehr kräftiger "Unterstützung" (diesen Text mußt Du bringen, sonst gibts keine Anzeige) der Hersteller einschließlich der davor oder danach "begleitenden" Anzeigen - hier vorgestellt bzw. ausführlich beschrieben.
Hier diese Geräte aus Heft 1 :
Sony Transistorized AM FM portable radio - Fisher Model 400-C stereo preamp - Reslo "Celeste," "Symphony/1 and "Avon" microphones - Knight KN-120 AM FM/Stereo tuner.


Transistors have completely dominated the market for portable receivers, and many units little larger than a package of cigarettes have appeared and been well received. Before the introduction of the Sony TFM-151, all have been AM receivers, employing up to eight transistors, and accommodating small built-in loudspeakers.

The TFM-151, however, sets a new standard for quality performance in a transistor portable. It uses fifteen transistors in a unique assortment of PNP and NPN types - eight in the FM tuner section, three in the AM tuner, and four in the a.f. amplifier.

The entire unit, shown in Fig. 1, measures 3x8x9" and weighs only 5 lbs. It is powered by four "D" cells with a total of 6 volts. The FM section, with its built-in telescoping antenna as well as provision for an external 75-ohm line, covers the range from 88 to 108 mc. It consists of an r.f. amplifier, mixer, and oscillator, followed by four i.f. stages with the last two doubling as limiters. Two germanium diodes follow as the discriminator, and its output is fed to a d.c. amplifier which varies the base bias on the oscillator to provide a.f.c. and also serves as an emitter-follower output stage for the FM section. All of the FM transistors except the d.c. amplifier/ follower are PNP types.

The AM section uses a ferrite loopstick, with additional provision for an external antenna. The circuit uses a PNP transistor as oscillator-mixer, followed by two NPN transistors as i.f. amplifiers, and a detector using a diode. An additional diode aids in providing a.v.c. action.

A button-actuated switch channels battery to the desired section, and at the same time connects the volume control to the AM or FM outputs. The arm of the volume control is fed to a three-terminal strip, the other terminals connecting to the a.f. amplifier input and ground.

The first two terminals are normally connected together with a jumper which may be removed to feed an external amplifier at tuner level.

The a.f. amplifier consists of two single-ended stages, transformer-coupled to a class B output stage, all employing NPN transistors, with a diode providing temperature compensation for the output stage. The output is 180 mw, which is adequate for the built-in 4x6 in. oval speaker. A jack permits use of an earphone, cutting out the speaker voice coil, which has an impedance of 3.2 ohms.

  • Anmerkung : Viel zu viel Information für den Leser, der das meiste davon gar nicht versteht, das war aber SONY - dem Anzeigenkunden - geschuldet.


Performance (bei einem Kofferradio ?? = Unsinn)

As a portable receiver, this Sony unit will compare favorably with any AM set we have ever seen with the possible exception of having somewhat less power than would be desirable if one expected to stage a dance at a weekend party at the beach or mountain cabin. For most uses it would be judged completely adequate, however.

What is remarkable is the quality, particularly on FM. With the output from the terminal strip connected to an Aux input of a typical hi-fi system, the quality compared directly with a high-quality standard FM tuner was such that they could not be told apart. Even when the output from the speaker-circuit jack was fed into the system - thus using the entire a.f. amplifier - the quality was still excellent, and there was no hum. This was due, undoubtedly, to the feedback around the output stage from the secondary of the transformer.

Sensitivity is comparable with any good FM receiver, and a.f.c. action is better than most. AM quality was nearly as good, allowing for the sideband cutting of two i.f. stages - but distortion was at a minimum. There is apparently no drift, since once a station is tuned in it stays there indefinitely, even after hours of playing and hours with the set switched off.

The Sony TFM-151 is the world's first transistorized AM/FM portable, and Sony deserves praise for both the design and construction. Figure 2 is an internal view of the printed-circuit construction. The AM "front end" is at the left of the gang capacitor, while the FM i.f. strip is the section just above the speaker magnet. The set could well serve for a model for any transistorized construction.

Fig. 1 (left). Sony TFM-151 AM/FM transistorized portable. Fig. 2 (right). Interior of 15-transistor receiver. Note speaker magnet frame projecting through opening in printed-circuit panel.


There has never been any question in the minds of well informed audiofans as to the generally high quality of Fisher equipment, and the 400-C Master Audio Control continues in the same tradition.

This is an attractive self-powered unit requiring a cutout 4 1/2" high by 14" wide and extending back from the panel some 7". It is available as a chassis for mounting in an existing cabinet as well as in wooden cabinets in various finishes, one being shown in Fig. 3.

This preamp-control unit has a number of unique characteristics, in addition to all of the normal facilities expected in a stereo control unit. One of the most interesting from the standpoint of the user who may have both changer and turntable is the equalization selector.

Two phono inputs are provided - and the requirements have been considered thoroughly by the designers to give the utmost in simplicity of operation.

One of the inputs has three degrees of equalization - RIAA, EUR and LP, with the latter two functioning only for monophonic pickups.

The RIAA position on this input may be used for either mono or stereo records. The second phono input has RIAA equalization only, and connections to two separate pickups may be left in place permanently even though the user has two record playing units.

  • Anmerkung : Damit würde sich dieser Vorverstärker zum Abspielen der alten Mono-Vinyl-Platten sicher eigenen.


Weitere Eigenschaften des 400-C

The tape input is for connecting directly to the tape heads, and correct equalization is built in so that all controls will be centered in the 400-C. The mic input is flat, and arranged to accommodate any high-impedance microphones. Both tape and mic inputs may be used for stereo or mono, as desired.

Provision is made for three high-level inputs, all dual-channel, and selection between inputs is made by a push-button switch, with pilot lights indicating which input is in use. A rumble filter is provided, with low-frequency cutoffs at 20, 50, and 100 cps, and the loudness contour is selected by another switch which gives two degrees of compensation as well as a flat position.

The remaining controls are: channel balance, bass, treble, volume and power switch, and an output selector switch. The latter has six positions: normal and reverse stereo, channel A feeding both outputs, channel A feeding channel A output alone, channel B feeding both outputs, and crossover. This last is just what the name implies, with a 650-cps crossover network switched in so that the channel A output has the highs rolled off and the Channel B output has the lows rolled off, both being fed from the channel A inputs.

This permits a stereophonic effect from mono sources, since the two speakers are reproducing different frequency ranges with a consequent distribution of the sound between the two channels.

  • Anmerkung : Das war natürlich ein völliger Unsinn, aber in der Werbung war es ein Argument.

The tone controls are the Baxendall type - which we prefer - and the contouring of loudness compensation is pleasant. Four a.c. (das sind die 110 Volt US-Buchsen) output receptacles are provided, all being controlled by the power switch, and accommodating a total of 650 watts which should be adequate for two amplifiers and a turntable and/or changer.

All heaters (except that of the rectifier tube) are fed from d.c. which is provided by a selenium rectifier and a filter system consisting of two 1000 uf capacitors and a 10-ohm resistor. The plate-supply filter is a two-section EC type, and residual hum is better than 80db below normal output of 2 volts for high-level inputs, and better than 60db below the normal output for the low-level inputs.

Tubes emploved are: four ECC83/12AX7,s, two ECC81/12AU7's, and one EZ80/6V4. The front panel is brushed brass, and is almost 1/8" thick. Cathode-follower outputs are provided for a tape recorder, feeding from both channels, and tape monitor jacks are furnished for use with recorders having feed-through connections built in.

Construction des 400-C

Figure 4 shows the top and rear of the chassis for the locations of input and output jacks. The Channel A connections are on the top row and Channel B connections are on the lower row, except for the tape monitor jacks which are shown at the left of the top row of jacks.

  • Anmerkung : Man sieht hier ganz deutlich, das dies die erste Generation von aus den Mono-Produkten nachgerüsteten Stereo-Verstärkern war. Da wurde hinten einfach eine Etage drauf geschraubt.

Level-set controls are used for the low-level inputs through the preamplifier, and for the aux 1 high-level inputs. These are shown on the housing in front of the tubes, and are accessible from the top. Both preamplifier tubes, shown on the platform at the right, are shock mounted for complete freedom from microphonics.

The 400-C is a real joy to use. The switching is quiet, with no noise between switch positions; controls are quiet and tapers have been chosen for smooth operation. The controls have a firmness of feeling, which gives the same impression as when handling a fine car.

Distortion is low - measuring around 0.1 per cent at a 1-volt output, and the equalizations of the two preamplifier sections in the model tested was closer than 1 db of being identical in both channels. All in all, we consider the 400-C to be one of the finest examples of preamplifiers we have been privileged to examine.

Fig. 3. The Fisher Model 400-C stereophonic Master Audio Control.
Fig. 4. Chassis view of the Fisher 400-C shows input jacks, level-set controls, and general layout.


New tuners seem to be introduced at the rate of about one each month, and aside from variations in appearance, quality of construction, and placement of controls, there is little to distinguish one from another. Performance is uniformly good, and while there are differences in sound quality, hum level, drift, and sensitivity, most of them use essentially the same circuits and many buy their i.f. transformers from the same source.

But every so often something that is sufficiently new to warrant attention appears, and the Knight KN-120 Deluxe basic AM/FM/Stereo tuner is one of them. For in this model there is a radically new idea which we have never before seen applied to tuners, although all of us are familiar with the use of feedback in amplifiers - in fact, we rarely see an amplifier nowadays without feedback.

Before discussion of the physical and performance characteristics of the KN-120, the application of feedback to a tuner should be explained, for it is in this area of circuit design that this tuner is distinguished.

Fig. 9. Allied Radio Corporation's Knight KN-120 Deluxe AM/FM/Stereo tuner.

Die neue a.f.c., die "automatic frequency control"

Reviewing briefly, most readers are aware that a.f.c. may be obtained by connecting - through suitable filtering circuits - the output of the discriminator to a reactance tube which controls the frequency of the h.f. oscillator in the "front end." The Foster-Seeley discriminator is so arranged that when properly adjusted its audio output is superimposed on a d.c. voltage whose average value varies as the center frequency of the i.f. channel is varied.

When tuned exactly "on the nose", the average voltage of the discriminator output is zero; if the set is tuned to one side or other of exact center - which means that the carrier is not distributed symmetrically over the straight-line portion of the discriminator curve - a d.c. voltage is developed. A reactance tube is a voltage-sensitive device which varies its basic characteristic - either inductance or capacitance, depending on the actual circuit - as the voltage applied to one of its elements is varied. If the tube is connected across an inductance in the oscillator circuit, the frequency of the oscillator can be varied by varying the control voltage. Thus the entire circuit functions like an engine with a governor in which a speed-proportional control is exerted on the engine's throttle to maintain a constant speed at all times.

In the FM tuner, the d.c. voltage from the discriminator is fed back in the proper polarity to correct oscillator frequency and thus to retune the circuits so that the i.f. signal is in the center of the i.f. pass band. As in any governor system, there must be some deviation in order for any control voltage to be developed, so it is not possible to provide a 100 per cent correction.

However, in a well-designed set the deviation can be held to less than 20 kc with ease. For the usual a.f.c. circuit, therefore, it is only the average d.c. voltage at the output of the discriminator which is employed for the control, and the average is obtained by filtering in the return circuit. As a matter of fact, we have seen sets in which the filtering in the a.f.c. return was inadequate, and some low-frequency audio signal was present in the control voltage.

The net result was that when the a.f.c. was switched on the low-frequency audio voltage in the control signal would try to move the intermediate frequency back to the center again with each signal variation, and since the discriminator can only detect frequency variation, the low-frequency output of the set was reduced. So every time the listener switched the a.f.c. on, the bass dropped out of the reproduction.

Supposing, however, that the audio output from the discriminator were to be fed back to the reactance tube. If there were no filtering in the line, and enough control voltage were fed back, the output would be reduced appreciably throughout the entire audio spectrum. However, if a controlled amount of the audio signal were to be fed back, it would serve the same purpose as any other type of feedback and should therefore reduce distortion and improve frequency response.

This is the principle of the Dynamic Sideband Regulation as employed in the KN-120 tuner. Some of the audio voltage from the discriminator (actually that from a cathode follower which offers a low-impedance source for the voltage being fed back) as well as the filtered d.c. voltage (which is proportional to the average deviation from center frequency) is fed back to the reactance tube to give about 10 db of audio feedback throughout the i.f. section and the discriminator.

und jetzt noch ausführlicher . . . . .

The result is that while the audio output is reduced by some 10db, there is a considerable reduction in noise from weak stations, and the effect of over-modulation is reduced greatly. While FM stations by and large radiate a cleaner signal than is usually heard on AM, some of them do occasionally increase their modulation to improve coverage, and they may exceed the i.f. amplifier bandwidth in the tuner.

There is a definite improvement in audio quality on most stations with the DSR turned on, and on fringe stations the signal-to-noise ratio is improved very noticeably. The FM section may be used without DSR, and with or without a.f.c, but since the operations are related, the DSR switch overrides the a.f.c. switch. Normal practice is to tune in a station with DSR and a.f.c. switches both at off; then switching the DSR switch to on also turns on the a.f.c.

General Description

Figure 9 shows the external appearance of the KN-120. Separate tuning knobs are used, and separate dial pointers and tuning indicators are used, as would be necessary on any AM/FM/Stereo tuner. In the lower panel, the lever switch at the left controls AM tuning, varying sensitivity and pass band for local, medium, or distant reception.

At the right is another lever switch that selects the output fed to a pair of jacks marked output on the rear - apron the FM jacks are normally connected to the FM circuit at all times. With this switch in the am or stereo positions, an AM signal is available at the output jacks. One jack of each pair is fitted with a level-set control. The three slide switches on the front panel control power, a.f.c, and DSR.

Figure 10 shows the rear of the chassis removed from its case, which measures 4" high, 15" wide, and 13" deep. The case is steel, with a leather-like vinyl material permanently bonded to it.

  • Anmerkung : Und jetzt kommt das sogenannte Kleingedruckte. Dieser FM-Stereo Tuner kann ja noch gar kein Stereo, denn der Multiplex Decoder fehlt ja noch, dafür hatten sie diese Buchse vorgesehen, zur Nachrüstung, wie später vor 1963 bei uns in Deutschland, also war das ebenso eine echte Mogelpackung.

A multiplex jack is provided, and the built-in ferrite loopstick is mounted on a pivot so it may be oriented for optimum signal pickup.

In conclusion, it must be said that the DSR feature, along with overall good design, results in a tuner which has adequate sensitivity and excellent audio quality. Furthermore, it is compact and attractive in appearance.

Fig. 10. Rear view of the Knight basic tuner.

  • Anmerkung : Diese Lobesspüche waren damit fehl am Platze, das Ding ist unterste Kategorie.


Equipment Profile - AUDIO • FEBRUARY, 1959

- Werbung Dezent -
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