US2342822A - Amplifying system - Google Patents

Amplifying system Download PDF

Info

Publication number
US2342822A
US2342822A US371498A US37149840A US2342822A US 2342822 A US2342822 A US 2342822A US 371498 A US371498 A US 371498A US 37149840 A US37149840 A US 37149840A US 2342822 A US2342822 A US 2342822A
Authority
US
United States
Prior art keywords
amplifier
receiver
battery
gain
tube
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US371498A
Other languages
English (en)
Inventor
Carl H Rumpel
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
AT&T Corp
Original Assignee
Bell Telephone Laboratories Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to NL68241D priority Critical patent/NL68241C/xx
Priority to BE471331D priority patent/BE471331A/xx
Application filed by Bell Telephone Laboratories Inc filed Critical Bell Telephone Laboratories Inc
Priority to US371498A priority patent/US2342822A/en
Priority to GB16139/41A priority patent/GB552331A/en
Application granted granted Critical
Publication of US2342822A publication Critical patent/US2342822A/en
Priority to FR942174D priority patent/FR942174A/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/06—Receivers
    • H04B1/16—Circuits
    • H04B1/1607—Supply circuits
    • H04B1/1623—Supply circuits using tubes
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/34—Negative-feedback-circuit arrangements with or without positive feedback
    • H03F1/36—Negative-feedback-circuit arrangements with or without positive feedback in discharge-tube amplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G3/00—Gain control in amplifiers or frequency changers
    • H03G3/02—Manually-operated control
    • H03G3/04—Manually-operated control in untuned amplifiers
    • H03G3/06—Manually-operated control in untuned amplifiers having discharge tubes
    • H03G3/08—Manually-operated control in untuned amplifiers having discharge tubes incorporating negative feedback
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R25/00—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception

Definitions

  • This invention relates to amplifying systems and the object of the invention is an improved amplifier for use in portable apparatus such as audiphones.
  • the volume level of the output is controlled by variable negative feedback so that for the lower sensitivities the feedback is greater thereby giving better quality of reproduction for those who have only slightly impaired hearing and who therefore are more likely to appreciate the better quality.
  • 'a circuit for introducing a positive feedback proportional to the internal resistance of the battery so that the gain of the amplifier is substantially independent of the battery resistance or may, if desired, be made to increase or to decrease slightly as the battery is expended.
  • the pick-up microphone is connected to the amplifier through an adjustable network which gives the user a choice of several low frequency transmission characteristics according to his personal requirements or the particular characteristics of the sounds he wishes to hear. In noisy locations this network may be set to give a large amount of low frequency attenuation, thereby discriminating against low pitched noises and the lower sound frequencies of the voice which contribute but little to intelligibility. This procedure permits of greater amplification of the higher frequencies without overloading.
  • Fig. 1 is a circuit diagram of an amplifying system according to the invention, using a crystal type receiver;
  • Fig. 1A shows an electromagnetic receiver adapted for use with the circuit of Fig. 1;
  • Fig. 2 shows the frequency response curves of the system
  • Figs. 3, 4 and 5 show the elements of the coupling network connected in various ways to produce the several different low frequency responses
  • Fig. 6 is a series of curves illustrating the use of feedback to control the volume and maintain a fiat response and high gain independently of the aid of the battery.
  • the pick-up microphone II is preferably of the piezoelectric crystal type which, as is well known, is a high impedance device and may be connected directly to an amplifier without the use of a transformer.
  • the microphone is coupled to the grid of the tube It by means of the adjustable network 13, the function of which will be described more in detail below.
  • sistance-capacity coupled and the output transformer It connects the tube IE to the magnetic type receiver I! of Fig. 1A in the conventional manner, or, alternatively, to the crystal receiver 44 in a novel manner to be described.
  • the battery l8 provides filament current for all three tubes and the battery I9 supplies the required voltages to the screen grids and plates through suitable resistors.
  • the primary of the output transformer is shunted by the potentiometer 20 by means of which an adjustable portion of the output energy may be fed back negatively .to the prior stages. path including conductor 2
  • the resistor 22 also passes plate current for the tube ll, thereby making it unnecessary to provide a separate resistive connection to the battery for this purpose.
  • the tubes I2, I! and i5 are re- Current flowing over the 21 to the negative side of the battery thereby impressing variable signal potentials on the screen grid 28 of the tube l2. These potentials are also in negative sense and therefore reduce the gain and distortion in all three stages.
  • the resistor 25 and the conductor 2! also provide a direct current path for the screen current of the tube l2.
  • the most important of which are at the screen grid 28 of the tube i 2 and the control grid of the tube H.
  • the feedback to the screen grid 28 will be negative, thereby reducing the gain of the amplifier even when the potentiometer is at its lowest or zero feedback setting.
  • the feedback potentials are impressed on the control grid of the tube is over a circuit including resistors 30 and 33 and the coupling condenser 34 in a postitive or regenerative sense.
  • the network i3, referred to above as providing the user with a choice of low frequency response characteristics, comprises a condenser 35, resistors as to 39 and a three-position switch I.
  • the problem of obtaining a high rate of attenuation of low frequencies in the input of this system is complicated by the very high impedance of the crystal microphone and the necessity for keeping the bulk and weight of the filter elements very small.
  • Conventional inductance and capacity networks are entirely impractical since they are too large and heavy and many case, to be eflective, they would have to be placed in the low impedance output circuit where they would not protect the tubes against overloading.
  • the more usual, simple resistance-capacity networks are unsuitable since when designed for the required low frequency attenuation they also attenuate the middle frequencies excessively.
  • the network l3 has been designed as a two section filter with the transmitter ll serving as the capacity rate of cut-off approximating twice that of a single section is obtained.
  • the two-section filter giving the high attenuation of low frequencies'shown by curve ll of Fig. 2 is used when the switch 40 is in position I, in which case the network is effective as shown in Fig. 3.
  • the system is designed to be used with either a magnetic type receiver I! or with a crystal receiver 44.
  • the contacts 45, u of the plug 41 are connected to the output terminals 48, ll of the transformer II in the conventional manner.
  • protection of the user from acoustic shock may be obtained by using a plug having a third contact III which connects one side of a limiting device 52 through terminal Ii and condenser ll to the plate terminal of the primary winding of the transformer.
  • the other side of the limiting device is connected to the negative terminal of the plate battery so that the device is effectively in shunt to the output of tube II.
  • This limiting device may be of any known type such, for example, as a non-linear resistor of the substanceknown as thyrite. the resistance of which decreases rapidly above a certain critical voltage. In cases where a more gradual limiting some other known form of limiter such as a thermal device the resistance of which varies with its temperature. 1
  • the crystal receiver 44 is electrically equivalentto a small capacity of the order of v 750ml! and its' impedance over the frequency range of 100 cycles to 10,000 cycles per second therefore varies from about 20,000 ohms to 2 megohms. As is well understood in the art an output transformer suitable for use with a magnetic receiver is therefore impractical for use with a crystal receiver.
  • the transformers necessary for coupling the magnetic receiver to the amplifier may be used with the crystal receiver in such a manner as to simulate the eii'ect of a constant K network.
  • a terminating resistance is connected across the secondary of the transformer and'the crystal receiver is connected across the amplifier output through a suitable blocking condenser.
  • the transformer should have a very high leakage reactance but since this would ordinarily require a transformer of considerable bulk there are practical limitations on the leakage reactance in cases where the bulk and weight must be kept small.
  • the value of the terminating resistance will depend on the con stants of the particular transformer used and other factors the optimum value can be readily determined by experiment. In one instance, for example, a very ood response characteristic was obtained with a very small transformer suitable for use with the magnetic receiver with a secondary shunting resistance of 60 ohms.
  • the shunting resistor 54 is, of course, not required when the magnetic receiver is used and because of the inherently limited output capacity of the crystal receiver, the voltage limiter is not required when the crystal is used.
  • the resistor and limiter are, therefore, associated with the individual receivers and are preferably built into the respective receiver plugs as indicated so that the necessary circuit changes are made automatically when either receiver is connected for use.
  • a transformer of high leakage reactance may be used in the manner described to apply a constant voltage to other capacitative loads such, for example, as crystal or capacity type loud-speakers.
  • Fig. 6 The advantages of this amplifier from the standpoint of high quality and sustained gain over the useful life of the battery are illustrated in Fig. 6.
  • curve 65 whenv the batteries are new'and the amplifier is operating at maximum gain, that is,- with no negative feedback, the response is'reasonably uniform from 100 to 10,000 cycles. This very large gain is very rarely, if ever, required, however, and as shown by curve 56, the response becomes much more nearly uniform when the output volume is decreased by only 5 decibels of negative feedback.
  • the response characteristic is, of course, still further improved as more feedback is used and with 25 decibels feedback there is no perceptible variation of gain as shown by curve 58 but the output level is still ample for a large proportion of audiphone users.
  • Curve 5'! shows the general configuration of the response curve for maximum gain when the batteries have deterioratedto a point where their voltage is only two-thirds of the new battery voltage. While this curve shows some reduction of low frequency response, this loss of gain is very much less than in prior audiphone I amplifiers and the circuit shows no tendency to oscillate. It will also be understood that while curve 51 shows an appreciable loss of gain as compared with the gain when using new batteriespthis is largely a matter of choice since it is quite feasible to use enough positive feedback to keep the gain practically constant over the whole range until the batteries are completely unfit for further use.
  • a pick-up microphone a vacuum tube amplifier having input and output circuits, a telephone receiver connected to the output circuit, a volume control comprising a variable negative feedback path within the amplifier for progressively improving the transmission characteristic of the amplifier as its gain is reduced and a network connecting the microphone to the input circuit, said network having an adjustabl low frequency attenuation whereby the low frequency output of the system may be connected to the output circuit ofthe m tube, a path conductive to both signal and direct current from the output circuit of the last tube to the output circuit or the second tube.
  • An amplifier comprising a plurality of vacuum tubes each having an input and an output circuit connected in tandem, a battery for energizing the tubes and a negative feedback path extending from the output circuit of the last tube to the input circuit of one tube and conducting current from the battery to the output circuit of another tube.
  • the combination with a crystal type microphone, a receiver and an amplifier having an input circuit connected to the microphone and an output circuit connected to the receiver, of a condenser serially connected to the other side of the input circuit and means for modifying the efi'ect of the resistance on the input circuit.
  • audiphone the combination with a crystal yp pick-up microphone, a receiver and a vacuum tube amplifier connecting the microphone to the receiver and having a substantially uniform transmission characteristic, of a network for adjusting the response of the audiphone over a limited range of low frequencies without aiIecting the transmission of other frequencies connected between the microphone and the amplifier and comprising a series condenser, a resistance ,by-passing the condenser, a resistive shunt arm connectedto an intermediate point on the resistance. and means for adjusting the effective resistance of the shunt arm.
  • an amplifier having input and output circuits, a pick-up microphone connected to the input circuit and a transformer having a secondary winding and a primary winding connected to the output circuit.

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Power Engineering (AREA)
  • Emergency Protection Circuit Devices (AREA)
  • Amplifiers (AREA)
US371498A 1940-12-24 1940-12-24 Amplifying system Expired - Lifetime US2342822A (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
NL68241D NL68241C (enrdf_load_stackoverflow) 1940-12-24
BE471331D BE471331A (enrdf_load_stackoverflow) 1940-12-24
US371498A US2342822A (en) 1940-12-24 1940-12-24 Amplifying system
GB16139/41A GB552331A (en) 1940-12-24 1941-12-15 Improvements in or relating to thermionic amplifiers
FR942174D FR942174A (fr) 1940-12-24 1947-02-03 Perfectionnements aux amplificateurs thermioniques

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US371498A US2342822A (en) 1940-12-24 1940-12-24 Amplifying system

Publications (1)

Publication Number Publication Date
US2342822A true US2342822A (en) 1944-02-29

Family

ID=23464205

Family Applications (1)

Application Number Title Priority Date Filing Date
US371498A Expired - Lifetime US2342822A (en) 1940-12-24 1940-12-24 Amplifying system

Country Status (5)

Country Link
US (1) US2342822A (enrdf_load_stackoverflow)
BE (1) BE471331A (enrdf_load_stackoverflow)
FR (1) FR942174A (enrdf_load_stackoverflow)
GB (1) GB552331A (enrdf_load_stackoverflow)
NL (1) NL68241C (enrdf_load_stackoverflow)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2481533A (en) * 1944-06-06 1949-09-13 Rca Corp Audio amplifier circuits for radio transmitters
US2541811A (en) * 1947-10-10 1951-02-13 Joseph W Crownover Hearing aid amplifier
US2710721A (en) * 1945-11-27 1955-06-14 Amasa S Bishop Electronic dividing circuit
US2761918A (en) * 1952-11-19 1956-09-04 Dictograph Products Co Inc Amplifier with gain control and power control
WO2007009483A1 (en) * 2005-07-21 2007-01-25 Freescale Semiconductor, Inc. Microphone amplification arrangement and integrated circuit therefor

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2481533A (en) * 1944-06-06 1949-09-13 Rca Corp Audio amplifier circuits for radio transmitters
US2710721A (en) * 1945-11-27 1955-06-14 Amasa S Bishop Electronic dividing circuit
US2541811A (en) * 1947-10-10 1951-02-13 Joseph W Crownover Hearing aid amplifier
US2761918A (en) * 1952-11-19 1956-09-04 Dictograph Products Co Inc Amplifier with gain control and power control
WO2007009483A1 (en) * 2005-07-21 2007-01-25 Freescale Semiconductor, Inc. Microphone amplification arrangement and integrated circuit therefor
US8085954B2 (en) 2005-07-21 2011-12-27 Freescale Semiconductor, Inc. Microphone amplification arrangement and integrated circuit therefor

Also Published As

Publication number Publication date
BE471331A (enrdf_load_stackoverflow)
NL68241C (enrdf_load_stackoverflow)
GB552331A (en) 1943-04-01
FR942174A (fr) 1949-02-01

Similar Documents

Publication Publication Date Title
JP2545344B2 (ja) 音響スピ−カ−を共鳴周波数以下で作動する方法及び装置
US3838215A (en) Speakers and crossover circuit
US2367110A (en) Audio amplifier system
US5305388A (en) Bass compensation circuit for use in sound reproduction device
US3571514A (en) Hearing aid tone control
US2342822A (en) Amplifying system
US2900609A (en) Tone compensated loudness control
US2121150A (en) Tone control system
US2589133A (en) Electrical filter
US3748399A (en) Telephone non-coil hybrid circuits utilizing active elements
US2101832A (en) Volume control circuits
US2065344A (en) Control means for signal control transmission systems
US2252002A (en) Telephone and other electric wave transmission systems
US2282382A (en) Amplifier system
US2547251A (en) Tone control
US2256057A (en) Tone control circuit
US3742153A (en) Telephone circuit for sidetone balance and automatic transmission level adjustment
US1931596A (en) Coupling circuit control
US2140969A (en) Hearing aid apparatus
US2074852A (en) Combined volume and bass tone compensation control device
US3487341A (en) Double loudness control network
US1788035A (en) Volume-control circuits
US2106785A (en) Electric filter
US2377121A (en) Tone and volume control means
US2266669A (en) Hearing aid device