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S'ept.V24,.1946. ‘ H, TOOMIM " ' . - 2,408,242 REGENERATIVE B‘A'SS COMPE'NYSATION CIRCUIT Filéd Dec. 30, 1944 2 Sheets-Sheet 1" A ' IN VEV TOR. HER3HEL TOO/VIM BYv Attorney 5. Sept; 24, 1946. I H_ mom -_ 2,408,242 REGENERA'I‘IVE BASS COMPENSATION CIRCUIT Filed Dec. 30, 1944 2 Sheets-Sheet 2 ' FIG. 2,. AUDIO INPUT lNVEN TOR. H5515"HfL TOO/‘#07 5; $2M”? I 2,408,242 ' Patented Sept‘. 24, 1946 ' ' _ V “UNITED , STAT E5 PAT E'N‘Tj *TFICE' in _ Hershel Toomim, Douglaston,‘ N.- Y., assignor, by mesneassignments, to. Remco Electronicylne, ' lflewYork, Haida corporation of New York A regenerating-December so, 1944, Serial No. 570,716 , " ' iz'olen'n's. (01.,179-1) I ' 2 Regenerative bass compensation. circuitsflsuch as shown, for example in Shepard Patent No. 2,313,098, have been found to be practical and efficient circuits for use inorder to drive a small V ; . ~ ' of 3a, regenerative‘ and degenerative feed a back between the‘screen grid and cathode of an audio ampli?er, to produce a desirable bass boost char acteristic, by the use of only, a minimum of addi loudspeaker to. reproduce lowerfaudio frequen tional elements. cies. , Such a regenerative compensation circuit ' Another feature of my invention is the ‘combi has the advantage that a volume compression ac tion as well as almost any-desired degree of com nation ,of a suitable humbucking or ?ltering T . v ' It has heretofore been suggested that such re , , means in such a circuit. pensation may be readily securedby regeneration over two stages of ampli?cation. ' In the drawings, , 10 f ‘ , , _, g, j I j Q Figure 1 is a circuit diagramillustrating a pre ferred embodiment of my invention; 7 ; ‘ Figure _2 is‘ a series of curvesillustrating the generative circuit be used in combination with operation of the circuits of my invention; and - degeneration derived from the voltage across the Figure 3 is a circuit diagram illustrating possi load impedance. This type of regeneration effec- ' I tively reduces the impedance from which the ‘load ~15 ble modi?cations of my invention. ' :In Figure 1, an incoming radio frequency sig works and therefore has va bene?cial damping effect. . ' ~ 7 ‘ ' ' ' nal, which-maybe the intermediate frequency ' Small radio receivers, of which the largestrvole _ . output of a heterodyne stage of a’ radio receiver, is indicated, asrbeingr appliedto the terminals I‘, ,2 ume is sold, generally use two audio frequency tubes, the ?rst of which :is a combination diode 20 at the left of’ the ?gure.‘ ,It will be understood that this will be the'output of the last inter; mediate frequency stage of a‘ superheterodyne radio receiver which embodies my invention. detector and triode ampli?er, and the other a power output tube. , The combination of the re generative anddegenerative feed backs. referred to above has heretofore beenproposed in circuits , The incoming intermediate frequency signal is adapted for use in such-sets. such-use,-a pen 25 recti?ed in tube 3 in the diode recti?er which comprises the anode 4 and cathode 5.- This is a tode has been proposed for use as the ?rst audio usuallrecti?er ‘circuit in accordance with stand tube, following the detector; In such arcircuit, ard practice. I 'An' A. V. ‘C. ‘voltage may be pro aswshown in Figurev 5, of the Shepard: patent duced [for use-linearly desired manner in accord-4 mentioned above, itis necessary. toiujse a sepa rate stage of detection prior'torthe audio pentode 30 ancegwith usual practice. Also in accordance withusual practice, the audio‘ frequency signal stage in order to be able to use the grids of the is applied through lead 8 and condenser ‘I to pentode for the various feed back voltages. ' ' ‘the ?rstjgridl? of thetube 3. This signal‘will It has also been suggested to use a duplex'di be ampli?ed in the tube sand supplied to the ode pentode tube as the ?rst audio tube, as shown in Figure 6, for example, of said Shepard patent. 35 power outputv tube 9 where it will be further am pli?ed andtranslated in the loudspeaker. This has, however, in circuits‘heretofore pro ' 'In-m‘y circuit I employa condenser C1 between posed, involved the sacri?ce 'of a; considerable the anode l3 ofthe .tube 3 and the grid I5 of the . amount of power, actually in Figure 6 of said .tube 9' which, as shown,'may have a preferred Shepard patent,asacri?ce1of 501% of the power. An object of'this invention is ;to'-provide a re 40 value of .004 microfarads in order to discrimi generative bass compensation 'circuit'which com-. bines the advantages of a degenerative feed back as mentioned above, but‘ eliminates the vdisad vantages of such combination.v By the use of my invention I am able to employ a combination di 45 ode pentode tube as the ?rst audio tube of ,a radio set having a power output tube, and ,avoid the disadvantages referred to above. ‘ Iam also?able to do this while providing excellent ‘?ltering, or nate in favor of the higher frequencies. The _volt ageapplied to the grid l5 will therefore have a characteristic of amplitude with respect to fre quency‘which is illustrated in curve A of Figure 2. This voltage will, of course, vary the plate cur- , rentandydue to the resistances l8 and L9 in the cathode leadof tube 9, the potential of the oath ode will vary accordingly. ,A portion of the volt ageacross the resistances I8 and I9 will be fed some other means of hum reduction, which is 50 back, through the lead 20 to the cathode of tube necessary, or at least highly desirable,,in ‘all bass boost ,ampli?ers _-as the regenerative bastsiboost makes the ‘ampli?er, highly susceptible topower supply'ripplei , ' _ ‘ 4; x '. ;g_ A feature of :myinventionisthe combination 3 in regenerative phase. Accordingly, these volt ages; will be further ampli?ed in the tube 3, as will beunderstood. j ; > - _ A dynamic loudspeaker 'of approximately 6 inches diameter‘willhave a resonance peak at 2,408,242 3 4 cessity of designing an intermediate frequency ampli?er, around combination diode-pentode low low audio frequencies and a second but lower resonance peak at high audio frequencies. I con nect the voice coil 2| of such a, loudspeaker through leads 22 and 23 and condenser H in gain tubes. It effects an increase in gain on the order of 2 to 1 with tubes now available, as well the circuit between screen grid 10 and ground to as being more economical. The use of the inverse speaker characteristic to select a regeneration frequency may be accom plished in other circuits, in which a triode or other type tube is used in either or both cir recognized as the resonance curve of such ‘a 10 cuits. One such circuit is shown in Figure 3 in produce an effective voltage between the grid in and cathode 5 in degenerative phase. The ef-. fective voltage fed back from the loudspeaker is indicated in Figure 2 by curve B, which will be , V which both the regenerative and degenerative-feed speaker turned upside down. The ‘curves have been shown’ in this form for‘; backs are applied between the grid and cathode of the tube 21. The operation of Figure 3 is convenience of explanation. It will be understood that the feedback represented ;by the-curve B is _ " otherwise substantially the same as that of Figure actually a negative feedback and',‘therefore, might 1.5., 1, and will" be understood therefrom. " iwhentriodesiare used, as shown in Figure 3, be shown below the zero line. If it were so shown the._sensitivity-to,power supply ripple is great then the total effective feedback atiany _fre-> enough to require excellent ?ltering or some other quency could be determined by simply adding curves A and B. Such an addition would show ' that, a maximum positive feedback occurs at fre type of hum reduction. Since neutralization is 20 difficult when the triode is used, I have shown, in Figure 3, the use of a ?lter circuit which, by quency F1 and again at frequency F5. It will be employinga condenser 29, may be made resonant understood that in thus transposing curve B to be to the principal ripple frequency, and therefore, below ‘the zero line, the left end of curve B as it ?lters this, frequency out to the. necessary extent appears in the ?gure will coincide with zero and . , the right end of curve B as it appears in the fig 25 at‘only a slight increase in cost. 'In'Figures l and 3 I have illustrated a portion ure will also coincide with zero. of the circuit in heavy black lines, which portion Curve C of Figure 2 indicates the voltage at the includes leads 22' and 23. from the voice coils control grid 15 of the output tube 9 ‘due to .the of the loudspeaker. It will be understood that in combination of curves A and B. It will be noted from Figure 2 that curves A and B cross at fre 30 feeding back a voltage from the voice coil inde generative phase, this voltage may befedback by quency f1 which will be a frequency of approx applying it at any point in the circuits de?ned imately 100 cycles. At or near this frequency by these heavy black lines. Wherever it is ap the effective voltage, due .to the combination of plied in this circuit its effect will be the same regeneration and degeneration, will have its max— imum as indicated by'curve C. Therefore, the 35 qualitatively. Its quantitative effect will be dif ferent, depending upon the impedance of the par loudspeaker output will be given an effective bass ticular speaker used. As a practical matter there boost at approximately this frequency‘. It may also be seen from Figure 2 that curves , fore the point at which this voltage will be in Band C again crosslat frequency is, which will be approximately 4000 cycles. There will accord ingly also be an accentuation of this frequency, serted will be chosen in accordance with the im pedance of a particular speaker it ‘is desired to which is desirable as it gives the loudspeaker characteristic the effect of crispness in repro In. Figure 3 I have indicated, in broken lines, a resistance 30 connected between the anodes of ducing speech. use with my circuit. the .two tubes. ' It will beunderstood that the regenerative voltage will be smaller than the degenerative voltage at all frequencies between the two speaker resonance points. The overall effect will there _ . Such a resistance so connected may beused to supply the degenerative feed back voltage re?ected from the voice coil, in which event the leads 22 and 23 will be .removed and the ‘resistances I8 and [9 connected. The im pedance ofithe loudspeaker will bereflected back in the pass band of the loudspeakerat which the 50 into the primarycoil connected to‘ the anode. of the output tube and thus modify the voltage ap overall effect will be degenerative. pearing at this anode. This volt-age will be fed In order to compensate for anode supply po back through the resistance 30 to the anode of tentials I provide condensers II and 25 and re tube 21 and thereby be introduced into the re sistance 26. 'Any hum potentials present will di generative loop indicated by the heavy lines. The vide between the condensers 24 and 25. These voltage thus introduced will be introduced in will be supplied to the grid 10 in phase to neu degenerative phase so that the operation of the tralize any potentials from the same sourc'eewhich fore be regenerative except for frequencies with circuit will be the same as before. may be applied to the anode l3. By a suitable It will be understood that while I have illus choice of values for the condensers 24 and 25 the hum may be minimized to the extent neces 60 trated specific circuits and particular values, my invention is capable of various modi?cations which will be understood by those skilled in the It will benoted that in my circuit I am using art. I do not desire, therefore, to be restricted the inverse speaker characteristic .to de?ne or to the particular details shown and described, but select a desired regeneration frequency, thereby eliminating the necessity for using special fre 65 only within the scope ofthe appended claims. It will, of course, be understood that conven quency selective networks for such a purpose, and tional systems of tone compensation, such as therefore eliminating the necessity for circuit elements that have previously been used in such tapped volume controls, etc., may be used in com bination with the circuits disclosed herein with circuits, while improving the characteristics of the circuits themselves. By applying all’ feed 70 the usual benefits. . back voltages to the screen of the pentode I also What is claimed is: make it possible to combine in such a tube a 1. An audio ampli?er circuit comprising an in diode detector operating in the usual fashion. put circuit, an audio ampli?er tube, and an out This is highly desirable as it permits the. use of put circuit, a transducer connected in said out standard tubes now available, and. avoids the ne 75 put circuit, means for regeneratively feeding sary. > a - 7 2,408,242 5 6 back to said ampli?er a voltage having a char acteristic which discriminates against fre quencies lower than thelow frequency resonance quencies higher than the low frequency resonance point of said transducer, means for degenerative recti?er circuit connected to the diode elements of said ?rst tube whereby said radio frequency voltage is recti?ed, means for applying said rec ti?ed audio frequency voltage to the control grid ~ of said ?rst tube whereby it is ampli?ed there in, a condenser connected between the anode of ly feeding back to said ampli?er a voltage hav said ?rst tube and the control grid of said sec point of said transducer and in favor of fre ing a characteristic which discriminates in favor ' ' ond tube, a pair of resistances connected in the I of frequencies higher than the low frequency cathode lead of said second tube, a connection resonance point of said transducer, and means 10 from the midpoint of said resistances to the cath ode of said ?rst tube, an output circuit connected for deriving said second voltage from said trans ducer. ‘ 2. An audio ampli?er circuit comprising a pair of ‘audio ampli?er tubes, a circuit which discrim inates in favor of high frequencies connecting the output of the ?rst tube .to the input of the > to said second tube, a loudspeaker connected in said output circuit, said loudspeaker having a voice coil, a condenser connected .to the screen grid of said ?rst tube, and a circuit connecting said voice coil between said condenser and said resistances. . second tube, an output circuit for said second 8. An audio ampli?er circuit as de?ned in tube, a transducer connected in said output cir claim 7, in combination with means for compen cuit, means for regeneratively applying a portion of the current from the output of said second 20 sating anode supply potential variations. 9. An audio ampli?er circuit comprising a pair tube to the input of said ?rst tube, and means of ampli?er tubes, the ?rst of said tubes being a for degeneratively applying a voltage derived triode, a circuit which discriminates against low from said transducer to the input of said ?rst frequencies connecting the output of said ?rst ' tube, whereby the overall frequency, response characteristic of said ampli?er circuit is a?ected 25 tube to the input of said second tube, means for regeneratively supplying current from the out by said transducer to produce a boost of low fre quency response. , ‘ t 3. An audio ampli?er circuit as de?ned in claim 2, in which the ?rst tube is a combination diode pentode tube, and a detector circuit con nected between the diode anode and the cathode of said tube. ~ . 4. An audio ampli?er circuit as de?ned in put of said second tube to the input of said ?rst 7 tube, an output circuit connected to said second vtube, a. transducer connected in said output cir cuit, and means for deriving a voltage from said transducer and applying said voltage degenera ~ tively to the input circuit of said ?rst tube, where .by the overall frequency response characteristic claim 2, in which the ?rst tube has a plurality of said audio ampli?er is affected by the imped of grids including a screen grid and a cathode,v and in which the feed back voltages are applied ance characteristic of said transducer. 10. An audio ampli?er circuit as de?ned in claim 2, in which the degenerative feed back volt between said screen grid and cathode. 5. An audio ampli?er circuit as de?ned in claim 2, in which the ?rst tube has a plurality of grids including a screen grid and a control grid, and in which the feed back voltages are applied between the screen grid and ‘cathode and no feed back is applied between the control grid and cathode. 6. An audio ampli?er circuit as de?ned in ‘claim 2, in which the transducer. voltage is intro duced into the circuit of the regenerated voltage. age is derived from said transducer and supplied ' to said ?rst tube by means of a resistance con nected between the anodes of said tubes. 11. An audio ampli?er circuit as de?ned in claim 7, .in which said degenerative voltage isv derived from said transducer and supplied to said ?rst tube by means of a resistance connected be tween the anodes of said tubes. 12. An audio ampli?er circuit as de?ned in claim 7, in combination with arecti?er and a power recti?er circuit having a ?lter section res 7. An audio ampli?er circuit comprising a com onant to the principal ripple frequency in the bination diode-pentode ‘?rst ampli?er tube and a power output tube, means for applying a radio 50 output of said recti?er. frequency voltage to the diode of said ?rst tube, a I-IERSHEL TOOMIM.