US1985999A - Audio frequency amplifier - Google Patents

Description

Jan. 1, 1935.

AUDIO l H. KRAMBEER FREQUENCY AMPLIFIER led July 16, 1950 E i I I I I I 4 feed-Back 1 Control 1 2 g u n -onfrol 25 Dev/be myth/77 f5 271' l INVENTOR flefecfbq KARL HE\NR\CH KRAMBEER ,2 BY)! D ATTORNEY Patented Jan. 1; 1935 invention to audio frequency amplifier adapted .to amplify .signal currents transmitted byradio; anduthe same serves the purpose to compensate such distortion as has been occasioned in :thenr'adio frequencyeamplifier and the rectifier by selectance driven unduly far i. e., 'byvundue selectance. I

Owing to the slight 'difierencein the frequencies, of..the carrier waves ofthe variousadjacent broadcast stations more or less perfect reception is feasible only by :the aid of means adapted to insure greater tuning sharpness or so-called selectance. In order that two transmitter 'stations may' be separated,. itis frequently necessary to push the selectance, beyond, the limit ewhere'tundistorted reception is still feasible The selectance of'the receiver apparatus becomes particularly. favorable if in'long-distancereception regenerative; couplingismade very .closefor the purpose ofzinsuring large volume. But distortion of both voice and music is then; inevitable. However, r it is chiefly the high frequencies that arehurt, and the result is that both, voice and W music are 1 dull-in reproduction. j p j In most instances it is impossible :to. dispense with high selectance in the tuningmeans; :Bllfiiif reception shall be made acceptable in spite of that there remains 110 Other remedythau to maker-an attempt to compensate such distortion as has been caused by undue selectance. p, p a v Now, according to the present invention, this compensation is insured in the audiofrequency part of the receiver in that, by additional circuit means, or by suitable dimensioning of-the normal transfer resistances, thedistortions v0cmtsionecl by undueselectance are compensated, It is then possible to work with maximum selectance in the radio frequency amplifier and this is especially important a for long-distance reception, Such supplementary circuit elements as are provided may be connected in parallel or in series with the plate or grid resistancesor else to the loudspeaker. It should here be noted that so far as the essen tial'featur'es of the basic idea of the invention are concerned itis immaterial whether the distortion is caused'in each stage or only inone stage. When :the selectance changes and thus also the distortion, say, owing to a change in regeneration, then, according to the invention; also the distortioncompensating meansare altered; this alteration being brought about in a positive manner. v In the .drawingwhich shows embodiments by way of example of the idea underlying this inven 'tion: I Figure 1 illustrates diagrammaticallyone preapplied to the circuit shown in Figure 1. I

. Accordingtto Fig. 1 in series 'withthe plate re-' ferred embodimentof my inveritionin which a resonant circuit is placed in the output-of fan 7 1 amplifirtube; t t. H J t FigureZ shows the invention diagrammatically withtheresonant circuit placed in the input of "5 anam'plifiertube'; Figure 3 illustrates anotherrembodi nentof the invention inlwhich the resonant" circuit is placed in parallel relation to the plate and grid resist ance;.* a Figure4i1lustrates'diagranrmatically my invention'as appliedto a transformer-coupled amplifier;

and, U 7 Figure 5 illustrates diagrammaticallya way-of obtaining 'variable distortion comp'ensation' as 5 sistance',;there isico'nnected astopper circuit comprising? condenseriC and coillLin parallel, in a resistance-coupledgaudio' frequency amplifier. 'If the circuit elements -are suitably proportioned, aniplification.i..for. the frequency 'range in [the neighborhood of resonance of the-stopper circuit may-.bel.lpromoted. Choosing a"resonanceifre'-' quency 5of arou1'id"f="8000; this makes it feasible to insure compensation of the distortion caused b'y undue-radio frequency selectance'H-In said c Figure 1 a first tube 1 preferably coupled to a source of energy to be amplified by'means of impedance 23is provided with an output circuit comprisingan impedance element 3, an inductance L'shuntedby' a condenser C and the 'usualsource of anode current; The anode of the tube 1 is connected to the grid element of a-second tube 2 through. coupling capacity l. impedance e1e ment 5 is connected-between the gridand cathode of the tube 2. Terminals; 6 and 7 representthe output terminals of thedevice to which may be connected anysuitable typeoftranslatingde'vice. From what has preceded it is obvious that the output'of'the tube lfis impressed upon the input oftube2. 4 I 1 j Thesame result is realized'if astopper circuitis connected hrseries with the grid leak as shown in Fig. 2. In Figure 2 the output circuit of tube 1 is provided with an impedance 22. As shown,- the anode of tuber-l isgconne'ct'edrto the 'grid of'tube 2 throughfi; coupling capacity? 4 and tube 2 11s provided with a gridtleak 21 series .With the stopper'circuitim; in-thecase of Figure: 1 termi '6 nals 6 and"? of 'Figure'2 are the outputf tenninals resistancearesonantcircuit (condenser and coilin series) is disposed which is tuned to a low frequency (Fig. 3). In Figure 3 two tubes 1 and 2 are shown cascaded through a coupling condenser 4.

.Tube 1 has connected between the anode and any suitable translating device may be connected."

The invention is useful also combination with transformer-coupled audio frequency amplifiers. As shown in Fig. 4 the desired compensation of distortion may here be accomplished by shunt ing the primary or the secondary'winding of the transformer by a condenser 20. In Figure '4 the tubes 1 and 2 are transformercoupled; purpose transformer T is provided with a 'p'ri rmary 17 which is associated with the output of tube 1 and a secondary 18 shunted by a; condenser 20, connected, between the; grid 1 and cathode. .of

tube2.,j

In the presence of suitable dimensions the selfcapacity of the transformer representedby condenser 19 shown in dotted lines may be utilized for this purpose so that additional circuit-ele-v ments for thatpurpose are dispensable.

As already pointedout radio frequency selectance and the distortion caused thereby depends markedly upon the feed-back setting of theaudion tube. The reception of long-distancestations, when. the regenerativecoupling is very close, is attended by far more distortion than is trueof local broadcasters- But if perfect reception shall be insured in all cases, then the antidistortion means hereinbefore disclosed/must be adjustableor regulable in sucha way that the degree'of distortion compensation must always be closely adapted to the feed-back. These simultae neoussettings may also be joined or made interdependent; in a positively, acting manner.

. Variable distortion compensation. may. be in-.- sured, for instance, in a circuit scheme of the kind illustrated in Fig. 1 by that a variable. high-ohm resistance is 'connectedin. parallel relationship; to the stopper circuit (Fig.5) g

1 'In Figurefi tubes land 2 are coupledthrough the sametypeof circuit as shown in Figurel. However, in this case there is provided a variable tone control device 8. The input of the tubev 1 is connected to the output of. -a tunable radio .frequencyjamplifier and detectorcircuit. 10 as'shown. The device-.10 is provided with a feedback control 13 connected to 10 through conductors 24 and 25. Device 13 is'shown variable and is adapted to be uni-controlled through a common shaft or other suitable interconnectingmeans 14 with the tone control; 8. Numerals 11 andu12 represent generally the antenna and ground of the usual radio receiver. i 7 Whereaudio frequency amplifiers having a-plurality of stages are employed the means hereinbefore disclosed may be inserted. either above or resulting in :giving the selector circuit such sharp selectance characteristics that signal Qenergy passed-,therethrough is distorted in various degreesdepending upon the adjustment of the se-& lectivity contrOLa detector and. an audi free quency amplifier, said audio frequency amplifier being provided with a resonant circuit the resonance characteristics of which tend to compensate for the radio frequency circuit signal distortion and means for varying the compensating characteristics of said resonance circuit simultaneously with thevariations adjustment of the selector circuit for the different degrees of selectivity whereby the signal distortion compensating "means varies simultaneously with the variations in theselectance characteristics of the selector circuit to thereby compensate for the various degrees of distortion.

2. Ina radio signalling system, a radio frequency circuit, adjustable means associated with 'said'circuit the operation of which affects the selectivity characteristics of said circuit, an audio frequency amplifier, means for controlling the -.tone o f -said amplifier and additional means for rendering said tone control means simultaneously operative with said adjustable means whereby the-tone control means compensates for any signal distortion caused. by adjustments in the said adjustable means. ..3. in asigna'lling systemincluding a:tunab1e selector circuit anda signal amplifier, an adjustable selectivity control means associated with the selector circuit, an adjustable distortion compensating means associated with the signal'amplifier and asingle means for adjusting both said last namedmeans simultaneously. 4. In .a radio :receiver, a tunable radio frequency circuit, adjustable means associated with said circuit, operation of said. adjustable means acting to affect the selectivity characteristic of saidcircuit, a detector, an audio frequency amplifier,. means for controlling the tone of said amplifier and additional means for rendering said tone control meanssimultaneously operative with said adjustable. means.

'5..Themethod of maintaining substantially uniform tone-fidelity in radio receivers and the like providedwith radio frequency and audio frequency amplifiers of the type wherein acharacteris'tic of theiradio frequency amplifier is controllable between two extreme conditions and wherein variations in said characteristic causes inherent variations in the selectivity characteristic of the amplifier which comprises simultaneously varying the ratio of high-to-low frequency response of the audio frequency amplifier with variations of the selectivity characteristic ofthe radio frequency amplifier.

6. In radio signalling apparatus, a radio frequency selector circuit provided with adjustable means operation of-which 'varies at least two characteristics of said circuit one of which is theselectivityof the circuit, an audio frequency circuit,- adjustable means for controlling the tonal characteristics of said audio frequency bin cuit and single means for renderin'g'the tone control simultaneously operative "with said first named adjustable means said tone control means acting to compensate for any signal distortion caused by adjustments in the first named means.

'7. In a radio receiver, a radio. frequency circuit, adjustable means associated with saidcircuit operation thereof acting to vary a charac teristic of said circuit, variations of said characteristic of said circuit also acting to vary the selectivity characteristic of said radio frequency circuit an audio frequency amplifier, means for controlling the tonal characteristics of saidampli-fier and means for rendering. the tOIIE'COI-IUIOI means simultaneously operative with said adjustable means whereby the tone control means compensates for anysignal distortion caused by changes'in the selectivity characteristics of said radio-frequency circuit.

8. A radio signalling system comprising in combination a radio frequency amplifien, an audio frequency amplifier, adjustable means associated with said radio frequency amplifier and operable by a control member acting upon operation to vary at least two different characteristics of the radio frequency amplifier, one i,

of said characteristics beingthe selectivity thereof, and means operable by said control member for varying the ratio of high-to-low frequency response of said audio frequency amplifier simultaneously with variations in the selectivity of the radio frequency amplifier to thereby compensate for any sign l distortion caused by vaamplifier. a 7

' KARL HEINRICH KRAMBEER.

riations in the selectivity of the radio frequency a 1

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