US1876675A - Audio amplification system - Google Patents

Description

Sept. 13, 1932. HlLER 1,876,675

AUDIO AMPLIFICATION SYSTEM Filed July 13, 1929 A T TORNEY Patented Sept. 13, 1932 UNITED STATES PATENT OFFICE EDWARD E. HILER, or BLOOMFIELD, NEW JERSEY AUDIO AMrLIEIcATIoN SYSTEM Application filed July 13,

transformer coupled push-pullaudio amplification wherein in the input circuit the secondary winding of an audio transformeris center tapped to the filament or ground porti on of the circuit and the outer terminals 0 this secondary winding are connected to the grids of the thermionic tubes. This arrangement eliminates the elfect of the generation of 1 secondharmonics in the electron orthermionic tubes, for by thus arranging the tubes in the circuit, the operation is such that during any one cycle'the voltage impressed on thegrid of one tube is increasing while that impressed on the grid :of the other tube is decreasing. The grid orinput circuits of the tubes are therefore, 180 degrees out of phase causing the fundamental currents in the two plate circuits to differ in phase by 180 degrees.- A

- center tapped coil may be used in the output circuit of the tubes in lieu of a transformer in which case the center tap of the coil is connected'to the positive terminal of a B battery, and the end terminals of this coil are v connected to the plates of the two tubes. With this arrangement, the fundamental signal in passing from the plate of'one tube through the output coil to the center tap is 180 degrees 7 out of phase with the fundamental signal passing from the plateofthe other tube to the center tap, Thus, owing to the push pull arrangement, the currents passing from the plates of thetubes through the sections of the coil are in phase, causing their magnetic fields to be additive as desired. However, the distortion produced in each of the tubes due to the curvature of the tube characteristic occurs at the same time and in the, same direction in each of the tubes with the result that second harmonicsgenerated in the tubes are in phase and are balancedout in the output circuit as desired. 1 The use of audio transformers in the input circuits of such amplification systems, however, results in more or less distortion due to the impossibility of obtaining one hundred 1929. Serial No. 378,058.

percent coupling between the primary winding andthe tapped secondary winding of the transformer. Furthermore, in using input transformers in such circuits it isgenerally necessary to employ resistances in shunt with the secondaries of the transformers in order to reduce the undesirable eflects of resonance peaks, the use of which resistances not only f thereof. I

I The principal obj ect of this invention is to provide a novelpush-pull audio frequency amplifier circuit employing double impedance coupling in lieu of transformer coupling. 1 a The use of double impedance coupling'has complicates the circuit but adds tothe cost decided advantages over transformer coupling one of which advantages lies in the elimination ofshunt resistances, since capacity coupling is employed instead of magnetic coupling, whichdesign eliminates the resonant speaks at the high frequencies. On account of not having a cut off at the high frequencies, the'range of frequencies made possible vby using double impedancecoupling can be extended to cover the wide band of fre quencies necessary for reproduction in high quality music and television applications.

By utilizing the method outlined in my prior Patent No. 1,715,501 the low audio frequencies. below 150 cycles can be exaggerated, if desired, to compensate for the normally poor. reproduction of low frequencies in loud speaker operation,

Other objects of this invention not at this timevmore particularly enumerated will be clearly understood from the following detailed description of the same.

, The invention is clearly illustratedin the accompanying drawing, in which Fig. 1 is a wiring diagram ofthe preferred form of the invention, and a f Fig. 2 illustrates an alternative manner of connecting a speaker or telephone receiver inthe output circuit. a Referring nowto Fig. 1 of the said drawing, the reference character 1 designates a threeelectrode thermionic electron tube or device which may be employed as adetector or as an audio amplification tube represent-v ing a stage of audio amplification. The grid 2 and filament or cathode 3 of tube 1 may be connected to any suitable input circuit, the output of which it is desired to amplify. The filament 3 of tube 1 may be heated by current supplied by a battery 14 while the plate or anode 4 of this tube is illustrated as supplied through a choke coil 15-with voltage from a"B"battery 16.

The plate 4 of tube 1 is connected through a coupling condenser 5.to the grid of athreeelectrode tube 6 arranged in opposition or push-pull relation with a similar 2 tube 7. Battery 14 is illustrated as supplying heating current to the filaments of tubes 6'and 7. The grid of tube 7 is connected through a grid choke coil Sand condenser 5 to the plate oftubel. The center of the grid choke coil 8 istapped and is connected from this midpointthroughaCbattery9 to the filaments oftubes 6 and 7 and therefore the potentials impressed on the grids of tubes 6 and 7 are 180 degrees out of phase, causing'the fundamental currents in theplate circuits of these tubes to differ by'180 degrees while the harmonics will be inphase. .Looked .at in an other way, the lower half of the grid choke coil 8 is ineffect the secondary of a one to one transformer, the primary of which is the upper half of the coil. The upper half of this coil servesas a grid choke for tube 6 while at the same time it is acting as a primary for'the lower-half of the coil. 7

The platesof tubes '6 and 7 are connected to'the terminals of an output choke coil 11. The center of'choke coil 11 is tapped and is connected through B batteries 12 and 16*to the filaments of tubes'G-and .7. Owing to the push-pull arrangement of tubes 7 6 and 7 though the fundamental currents in the plate circuits of these-tubes differ by 180 degrees, yetthe-magnetic fields set up by these currents in the outputchoke coil 11 are. additive while those set up by-the "harmonics are opposed and :ofi'setach other.

A lould speaker or-telephone 13 is illustrated {as connected in shunt'acrossthe terminals of outp-ut choke coil ll-for reception purposes. I

In operation, the output of tube 1 Vimpresses 1 {an alternating current potential across choke .coilf1'5. Since condenser 5 and choke coil '8 are connected through common batteries, these members .are arranged in shunt with choke coil 15 andtherefore an alternating current potential of substantially the same-value asimpressedacross coil15 is impressed uponchoke coil -8 since there is but little 'drop in potentialacross condenser 5. An -alternating currentpotential'is there fore applied to the grid of thermionic device 6. Since'the lower halfof coil SJ-is magnetically coupled tothe'uppen-half thereof, :an alternating current potential is" impressed on the grid of'tube 7- which potential 110W- .As; is well known to those skilled in the art the voltages impressed on the grids of these tubes generate harmonics which are in phase and which therefore balance out in the output circuit. I

It will be apparent that the loud speaker or telephone13 may be connected inthe output circuit in various other ways other than that shown in Fig. 1. That is, there are various ways of completing theoutput circuit from the points 'AA of Fig. 1. For example, as shown'in Fig. 2 of the drawing a different type of circuit arrangementis employed-from the points,AA.. In this arrangement the center tapped-output "choke coil is climinated'and in lieu thereof: impedances 16 and 17 ,illustrated .as choke coils, may be employed. Choke coils 16 is connected to the plate speaker circuit oftubefi whereas choke coil 17 is connected tothe plate speaker circuit of tube 7. In operation, the fundamental currents in'these plate speaker circuits are additive in the posed-and hence cancel one another.

It is obvious that non-inductive resistances may be used in lieu of choke coils 16 and 17 if desired. Also many other waysv may be employed for completing the circuit from the points AA,as for instance by using an output transformer with-the primary'wind ing center tapped to the output of the tubes. Although the electrodes of the thermionic devices are illustrated for the sake-of :simplicity, as supplied with'electric energy from battery sources, it is to be understoodthat normally an a. c. supply would be'employed.

As many changes could be. made in the above construction and many apparently widely different embodiments of this invention could be made withoutdeparting from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrativejand not in a limiting sense.

What is claimed is 1. An electrical amplification system comprising in combination, an electron discharge device adapted to have its IlCl andcathode elements connected'toan input circuit, an

tial through said anode choke coil, a condenser, and transformer'means, said 'transformer means having a primary winding and a secondary Winding, said condenser and said primary winding being arranged in parallel with said anode choke coil, a pair of oppositely arranged electron discharge devices having cathode-grid circuits, one of said discharge devices having its cathodegrid circuit connected across the primary winding of said transformer means and the other of said discharge devices having its cathode-grid circuit connected across the secondary winding of said transformer means.

2. In a push-pull double impedance circuit for audio amplification, in combination, a pair of thermionic tubes having cathodegrid circuits, transformer means having primary and secondary windings, said transformer means having its primary winding included in one of said circuits, and its secondary winding included in the other of said circuits, a coupling condenser for coupling said thermionic tubes to a signal circuit, a plate choke coil, said plate choke coil being connected to said coupling condenser, and said transformer means primary winding serving as a choke coil forone of said cathode-grid circuits.

3. In an audio amplifier circuit, in combination, a pair of electron discharge devices, each of said devices having a grid element together With a cathode and anode, external circuits extending between the oathode and grid elements ofeach of said devices, and transformer means having a primary winding and a secondary Winding solidly connected in series, said transformer means having its primary winding connected in the external circuit of one of said devices and its secondary winding connected in the external circuit of the other of said devices, and a coupling circuit connected at one side to the primary winding of said transformer means and at the other side to the cathode elements of said devices, whereby the primary winding of said transformer means isarranged in series with said coupling circuit. 7

4. In an audio amplifier circuit, in combination, a pair of electron discharge de-. vices connected in opposition, each of said devices having a grid element together with a cathode and anode, external circuits extending between the cathode and rid elements of each of said devices, an transformer means having a primary winding and a secondary winding solidly connected in series, said transformer means having its primary winding connected in the external circuit of one of said devices and its secondary winding connected in the external circuit of the other of said devices, and a coupling circuit having a condenser therein, said coupling circuit being connected at one side to In testimony, that Iclaim the invention set forth above I have hereunto set my hand this 12th day of July, 1929.

EDWARD E. HILER.

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