US2342239A - Producing sound records in half-wave records - Google Patents

Description

Feb. 22, 1944. c. BECKER 2,342,239

PRODUCING SOUND RECORDS IN HALF-WAVE RECORDS Filed Aug. 27'. 1940 2 Sheets-Sheet 1 Jnranfar 6. 3e c /(e 7 3y- 4w,

Feb. 22, 1944. c. BECKER 2,342,239

PRODUCING SOUND RECORDS IN HALF-WAVE RECORDS Fi led Aug. 27, 1940 I 2 Sheets-Sheet 2 J/Wen/or:

mama m. a, i944 PRODUCING SOUND RECORDS IN HALF-WAVE RECORDS Carlheinz Becker, Berlln-WilmersdorLGermany; vested in the Alien Propcrtyflnstodian Application August 27, 1940, Serial No. 354,459 In Germany March 18, 1939 lclaim.

The present invention relates to sound recording and, particularly, to the making of half-wave records which are referred to as push-pull class B records.

An object of the invention is to avoid disturbances and distortions which previously occurred when the alternating current is divided into two half waves.

Other objects and advantages will be apparent from the following description of detailed embodiments of the invention, when read in connection with the accompanying drawings, inwhich:

Fig. 1 shows a circuit for producing half-wave records, and Figs. 2 to 6 show different embodiments of the invention wherein the disturbances and distortions are avoided.

Referring to the left-hand side of Fig. 1, ,tli'e previously amplified microphone voltage is applied their respective windings.

across a resistance unit- I which is connected between the cathode and grid of an amplifier tube 2. The cathodeanode-circuit of tube 2 is formed by a battery 3 and the primary winding 4 of a push-pull transformer having two secondary windings 5 and 8. Winding 5 is connected across a resistance 9 with one side being connected through a diode I; similarly, winding 8 is connected through a diode 8 across a resistance It.

The diodes allow currents to pass in one direction only with the result that, during one half of each cycle, current flows from winding 5 through diode 1 and resistance 9; and, during the other half of each cycle, current flows from winding 8 through diodB 8 and resistance III. This produces onehalf wave voltages across resistances 9 and In which are supplied to the recording mechanism.

It has been found that this arrangement for producing sound recordings in half-wave records has the following disadvantages:

At each reversal of the current flow through the I transformer, the diodes I and 8 operate in such a manner that one of the push-pull circuits is cut in and the other is cut out. Due to the fact that substantial power is required for operating the recording mechanism, considerable current flows with the result that the effect oi cutting in and cutting'out the circuits is appreciable. In each of windings I and I. the self-induction tends to cause disturbances in the push-pull circuit itself as well as through a reactive effect in the other is provided for a circuit such as that shown in Fig. 1 Here, the transformer is designated at 3; Each push-pull circuit is provided with a second parallel circuit, there being a circuit formed by diode 'l' and a resistance 9' connected in parallel with the circuit, of resistance 9 and diode 1 and there being similarly a circuit formed by a diode 8' and a resistance [0' which is connected in parallel/with the circuit of resistance 10 and resistances lfl and ID are similarly related. During operation, the auxiliary parallel circuits formed by diodes I andiresistance 9' and diode 8' and resistance l0 respectively draw current from In the embodiment of Fig. 3, the two push-pull circuits are supplied through separate transform- .ers'3 and 3', respectively, transformer 3' having a primary winding 4'. Primary winding 4 receives current through tube 2 and primary winding 4' receives current through a similar tube 2. By

this arrangement, the change of 'current in one of the secondary windings does not eiiect the other transformer. In this way,.the major source of the distortion is eliminated.

The further modification of Fig. 4 avoids the disturbances by the'connection of the diode circuits. As indicated above in connection with the discussion of Fig. l. the disturbances and distortions depend in part on the intensity of the current flowing in the push-pull circuits and it is desirable to. maintain these currents as small as possible. However, due to the fact that considerable power is required to operate the recording push-pull circuit. These various disturbances of the mechanisms which are connected to resistances l and II, it is desirable that these currents be large and in the embodiment of Fig. 4 very high ohmic values are chosen for resistances 8 and II with the result that small currents flow through these resistances and no substantialdis tortion o'r disturbance results. Resistance 9 is connected across the cathode-grid circuit of an amplifier tube ll, the-cathode-anode circuit of which is connected to a battery across a resistance I 3; similarly, resistance I0 is connected across the cathode grid circuit of an amplifier tube I! which has its cathode-anode circuit connected through the battery across resistance It. Changes in voltage across each of the resistances 0 and I0 cause corresponding changes in the voltage across the respective resistances I! or H, and s uiiicient power is available from the circuits of hettery.

This defect is arm in occordance with the present invention by inserting in each or the diode circuits an adjustable negutive countervoltege-which is of such e value that theefi'ective operating characteristics of the, diode pess through the zero point.

Referring to Fig. 5, the common line between the, push-=pull circuits is provided with a. counter voltage unit. unit is formed by potentiometer 655 which hes connected across its ends.

e. hotter it. By adjusting the contact on the notentiometer, the proper voltage is placed in series in the diode circuit so thet the effective operating characteristics of the diodes i and 8 pass through zero. In this way, the diodes eliow a flow of current in one direction only.

In making records, it is necessary to supervise the half-wave voltages which ere impressed upon the recording device. In the illustrative embodiment of the invention represented in Fig. 6, the two half waves are composed intoe complete curve again and the resultant voltage is supplied by way of an amplifier to a control memloer such as a Breun tribe or a. loud speaker. 'Ihis composition is eil'ected in a simple manner by providing'o. circuit such as described above and the includ ng in each of the push-pull circuits 8. takeofl circuit parallel to the output from which the either at resistances 9 It or at resistances l1 and it. Volteges for control v w are taken on through condensers 22 and are impressed upon the grids of tubes l9 and so which are arranged in push-pull fashion. The two enodes oi tubes 89 and it are connec to the opposite ends of the primary windings of transformer 2i. and the center top is connected to one side of the other side of the battery is connected to the cathodes oi the two tuhes end else to the we line of the resistances 9 end it.

- to the grids of tuhes it] end it; form a complete half-wave is impressed upon an amplifier circuit.

Referring particularly to Fig. 6, the recording members are supplied with half-wave voltoges The secondary i 11-: of transformer H is connected to the control memher. El g operetion, the half-wove voltages which occur at resiston c m it end 08 are displaced 180." and the half-wove voltcges occng ot the resistances 9 end [it] respechvely, end the voltages applied were. Condensers 22 ere ler in their cherecteristics so that voltages of equol magnitude are topped from resistances it and as and re sistences 9 and G6,.

What 1 clnim is:

In a push-pull amplifying circuit of the type including a. transformer having its primary connected to a, source of speech currents and its divided secondary applied w wetricelly in push pull coupling to e pair of rectifier tub-es and loeding resistors in series connection therewith, whereby a halt-wove signal oppeers across one of the loading resistors and the. corresponding half-wove signal of opposite polarity eppeers across the other loading resistor, means for reducing distortion during amplification said means comprising a. shunt circuit consisting of a. rectifier and e. loading resistor connected across each half of the divided secondary, whereby currents of opposite polarity to the half-wave signal are dissipated in the resistor which forms a, port of the shunt circuit.

CZ BECKER.

Images