US2490943A - Dual microphone system - Google Patents

Dual microphone system Download PDF

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Publication number
US2490943A
US2490943A US8399A US839948A US2490943A US 2490943 A US2490943 A US 2490943A US 8399 A US8399 A US 8399A US 839948 A US839948 A US 839948A US 2490943 A US2490943 A US 2490943A
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microphone
amplifier
condenser
cathode
tube
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US8399A
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Warren B Bruene
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Collins Radio Co
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Collins Radio Co
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00—Circuits for transducers, loudspeakers or microphones
    • H04R3/005—Circuits for transducers, loudspeakers or microphones for combining the signals of two or more microphones

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  • This invention relates to microphone-amplifier systems and more particularly to such systems for use with microphones of different characteristics.
  • a principal object of the invention is to provide a microphone-amplifier system which is capable of producing substantially uniform output regardless of Whether the input is provided from a carbon microphone or a dynamic microphone.
  • Another object is to provide a microphone-amplifier system wherein the amplifier is arranged to be driven either by a dynamic microphone or a carbon microphone, together with switching and circuit arrangements for rendering the output of the amplifier substantially uniform for either of the types of microphones that is used.
  • a feature of the invention relates to an amplifier which is adapted to be driven either by a dynamic microphone or a carbon microphone, together with adjustable circuit arrangements common to both microphone inputs for producing substantially uniform output from the amplifier regardless of which microphone is being used.
  • a further feature relates to the novel organization, arrangement and relative interconnection of parts which cooperate to provide an improved dual microphone amplifier system.
  • an amplifier tube l which. may be of any well-known type, and
  • the dynamic microphone 2 is connected across the control grid 3 and the cathode E of tube i, a suitable high resistance grid leak 5 being provided across thegrid and cathode.
  • the direct current supply for the plate or anode 6 is represented schematically in the drawing by the battery 7, the negative terminal of which is grounded and the positive terminal of which is connected to the primary winding 8 of an audio frequency coupling transformer 9 and thence to the plate 5.
  • the secondary Winding ill of this transformer can then be connected to any suitable additional amplifier stage as may be required.
  • the necessary bias between the grid 3 and cathode i is achieved by means oi'the usual cathode bias resistor I I connected between the cathode i and ground, this bias resistor. ll being shunted by the condenser l2, under control of the single-pole single-throw switch i3, which is closed when the dynamic microphone 2 is being used. Under these conditions, the tube I acts in' the well-known manner to amplify the signals applied to the grid 3 from the dynamic microphone.
  • the switch I3 When it is desired to use the carbon microphone E, the switch I3 is opened. It will be observed that a part of the direct current from the power source I flows to ground through the resistors l5, H3, in series, which therefore act as voltage dividers.
  • the microphone I4 is connected across the resistor It to supply the necessary power for that microphone.
  • the sound waves incident upon the microphone l4 produce audio frequency variations which are coupled through the adjustable resistor l l and thence through the condenser l2 to the cathode 4, thus driving the cathode 4'. in accordance with these audio frequency signals.
  • the condenser l2 which normally would function as the by-pass condenser for resistor ll as above described, now functions as a direct current blocking condenser between the carbon microphone l4 and the driven cathode 4.
  • This method of driving the tube 1 by variation of the cathode potential 4 results in lower gain from the tube l.
  • this is a desirable eifect in the system as disclosed, since normally the carbon microphone l4 would produce a higher audio output at its terminals for a given sound wave incident thereon, as compared with the same sound wave incident upon the dynamic microphone.
  • By adjusting the resistor I] it is possible to maintain the output from transformer 9 substantially uniform regardless of which of the two microphones is being employed.
  • the condenser l2 therefore performs the double function of acting as a by-pass condenser when the dynamic microphone is being used and as a direct current blocking condenser when the carbon microphone is being used.
  • dynamic microphone means any microphone which does not require a separate battery or power source to render it effective; and includes any of the well-known types of microphones which generate a voltage in response to impinging sound waves, e. g., crystal microphones, ribbon microphones, moving coil-magnet microphones, velocity microphones and the like.
  • a microphone amplifier system comprising a grid-controlled amplifier tube, a microphone of the dynamic type, another microphone of the type which requires a local source of direct current power, and a two-position switch for operatively connecting either microphone to the input of said amplifier while maintaining the amplifier output substantially uniform for a given sound input regardless of which microphone is being used, and circuit connections operative when said switch is closed in one position to connect said other microphone only capacitively to the cathode of said amplifier tube.
  • a microphone amplifier system comprising a grid-controlled tube, a microphone of the type which generates voltage in response to impinging sound waves, a carbon microphone which varies the resistance in an associated direct current supply circuit, means comiecting the first-mentioned microphone to drive the control grid of said tube, means including a series coupling condenser 4 connecting the second-mentioned microphone to drive the cathode of said tube, and switch means for operatively connecting either of said microphones with said amplifier.
  • a microphone amplifier system comprising a grid-controlled amplifier tube, a microphone of the dynamic type, a microphone of the nondynamic type, a cathode bias resistor for said tube, a by-pass condenser for said resistor, a two-position switch, circuit connections efiective with said switch in one position for operatively isolating the non-dynamic microphone from the amplifier and connecting said condenser across said resistor, and other circuit connections effective when said switch is in another position for operatively connecting said non-dynamic micro- 4 phone to the cathode of said amplifier through said condenser while removing said condenser from across said resistor.
  • a microphone amplifier system comprising a dynamic microphone, a non-dynamic microphone, a grid-controlled amplifier tube for both microphones, said tube having a cathode bias resistor, means including another resistor and a condenser connecting said non-dynamic microphone in series between said cathode and ground, a two-position switch, circuit connections effective in one position of said switch to isolate said non-dynamic microphone from said cathode and simultaneously connecting said condenser in shunt to said bias resistor and other circuit connections effective when said switch is in another position to disconnect said condenser from said bias resistor.
  • a microphone amplifier system comprising a dynamic microphone, a non-dynamic microphone, a grid-controlled amplifier tube for both microphones, a switch for selectively rendering either of said microphones effective on said amplifier, a cathode bias resistor and shunt condenser for said tube, means effective with the switch in one position to drive the grid of said tube by the output of said dynamic microphone, means effective with the switch in another position to drive the cathode of said tube by the output of said non-dynamic microphone, said switch when in said other position disconnecting said condenser from across said bias resistor.
  • a microphone amplifier system comprising a pair of microphones of difierent signal outputs, a grid-controlled amplifier tube for both microphones, a bias resistor connected between the cathode of said tube and ground, means connecting one microphone across the grid and ground, a condenser, a two-position switch effective in one position to bridge said bias resistor by said condenser and efiective in another position to disconnect said condenser from across said resistor, and means connecting the other microphone effectively in series with said condenser and cathode when said switch is in said other position.
  • a microphone amplifier system according to claim 6 in which an adjustable resistor is connected in series between said other microphone and said condenser for equalizing the outputs of the amplifier regardless of which microphone is being used.

Description

- Dec. 13, 1949 w. B.- BRUENE DUAL MICROPHONE SYSTEM Filed Feb. 14, 1948 DYNAMIC MICROPHONE I Em OUTPUT TO NEXT AMPLIFIER CARBON- MICROPHONE INVENTOR WARREN B. .BRUENE ATTORN Y Patented Dec. 13., 1949 UNITED STATES PATENT OFFICE DUAL MICROPHONE SYSTEM Warren B. Bruene, Cedar Rapids, Iowa, assignor to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Application February 14, 1948, Serial No. 8,399
7 Claims.
This invention relates to microphone-amplifier systems and more particularly to such systems for use with microphones of different characteristics.
A principal object of the invention is to provide a microphone-amplifier system which is capable of producing substantially uniform output regardless of Whether the input is provided from a carbon microphone or a dynamic microphone.
Another object is to provide a microphone-amplifier system wherein the amplifier is arranged to be driven either by a dynamic microphone or a carbon microphone, together with switching and circuit arrangements for rendering the output of the amplifier substantially uniform for either of the types of microphones that is used.
A feature of the invention relates to an amplifier which is adapted to be driven either by a dynamic microphone or a carbon microphone, together with adjustable circuit arrangements common to both microphone inputs for producing substantially uniform output from the amplifier regardless of which microphone is being used.
A further feature relates to the novel organization, arrangement and relative interconnection of parts which cooperate to provide an improved dual microphone amplifier system.
Other features and advantages not particularly enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims.
In certain types of communication apparatus, for example in voice frequency amplifiers, modulators and the like, it is sometimes necessary to derive the input signals either from a dynamic microphone or a carbon microphone. One of the drawbacks to the use of these two different types of microphones is that they require different amplifier gains in order to produce the same output from the amplifier. The dynamic type microphone requires a greater gain than does the carbon microphone, but the carbon microphone requires a separate source of power such as a battery in order to render it operative.
There is shown in the drawing a microphone amplifier system wherein the amplifier may be driven by either type of microphone while at the same time preserving substantial uniformity of output regardless of which microphone is used. For this purpose, there is provided an amplifier tube l which. may be of any well-known type, and
while the drawing shows this tube as of the triocle indirectly heated cathode type, it will be understood that any other well-known type of amplifier tube may be employed. The dynamic microphone 2 is connected across the control grid 3 and the cathode E of tube i, a suitable high resistance grid leak 5 being provided across thegrid and cathode. The direct current supply for the plate or anode 6 is represented schematically in the drawing by the battery 7, the negative terminal of which is grounded and the positive terminal of which is connected to the primary winding 8 of an audio frequency coupling transformer 9 and thence to the plate 5. The secondary Winding ill of this transformer can then be connected to any suitable additional amplifier stage as may be required. The necessary bias between the grid 3 and cathode i is achieved by means oi'the usual cathode bias resistor I I connected between the cathode i and ground, this bias resistor. ll being shunted by the condenser l2, under control of the single-pole single-throw switch i3, which is closed when the dynamic microphone 2 is being used. Under these conditions, the tube I acts in' the well-known manner to amplify the signals applied to the grid 3 from the dynamic microphone.
When it is desired to use the carbon microphone E, the switch I3 is opened. It will be observed that a part of the direct current from the power source I flows to ground through the resistors l5, H3, in series, which therefore act as voltage dividers. The microphone I4 is connected across the resistor It to supply the necessary power for that microphone. The sound waves incident upon the microphone l4 produce audio frequency variations which are coupled through the adjustable resistor l l and thence through the condenser l2 to the cathode 4, thus driving the cathode 4'. in accordance with these audio frequency signals. Thus, the condenser l2 which normally would function as the by-pass condenser for resistor ll as above described, now functions as a direct current blocking condenser between the carbon microphone l4 and the driven cathode 4. This method of driving the tube 1 by variation of the cathode potential 4, results in lower gain from the tube l. However, this is a desirable eifect in the system as disclosed, since normally the carbon microphone l4 would produce a higher audio output at its terminals for a given sound wave incident thereon, as compared with the same sound wave incident upon the dynamic microphone. By adjusting the resistor I], it is possible to maintain the output from transformer 9 substantially uniform regardless of which of the two microphones is being employed.
When the system is being used, it is not necessary to adjust the resistor I! for each transmission. It may be initially set to produce the same gain for a given intensity of sound upon each microphone and when once set, it can remain in its adjusted position. Consequently, all that is necessary to switch from the dynamic microphone input to the carbon microphone input is to open the switch IS. The condenser l2 therefore performs the double function of acting as a by-pass condenser when the dynamic microphone is being used and as a direct current blocking condenser when the carbon microphone is being used.
The expression dynamic microphone as employed in the specification and claims means any microphone which does not require a separate battery or power source to render it effective; and includes any of the well-known types of microphones which generate a voltage in response to impinging sound waves, e. g., crystal microphones, ribbon microphones, moving coil-magnet microphones, velocity microphones and the like.
While one particular embodiment has been described, it will be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention.
What is claimed is:
1. A microphone amplifier system, comprising a grid-controlled amplifier tube, a microphone of the dynamic type, another microphone of the type which requires a local source of direct current power, and a two-position switch for operatively connecting either microphone to the input of said amplifier while maintaining the amplifier output substantially uniform for a given sound input regardless of which microphone is being used, and circuit connections operative when said switch is closed in one position to connect said other microphone only capacitively to the cathode of said amplifier tube.
2. A microphone amplifier system, comprising a grid-controlled tube, a microphone of the type which generates voltage in response to impinging sound waves, a carbon microphone which varies the resistance in an associated direct current supply circuit, means comiecting the first-mentioned microphone to drive the control grid of said tube, means including a series coupling condenser 4 connecting the second-mentioned microphone to drive the cathode of said tube, and switch means for operatively connecting either of said microphones with said amplifier.
3. A microphone amplifier system, comprising a grid-controlled amplifier tube, a microphone of the dynamic type, a microphone of the nondynamic type, a cathode bias resistor for said tube, a by-pass condenser for said resistor, a two-position switch, circuit connections efiective with said switch in one position for operatively isolating the non-dynamic microphone from the amplifier and connecting said condenser across said resistor, and other circuit connections effective when said switch is in another position for operatively connecting said non-dynamic micro- 4 phone to the cathode of said amplifier through said condenser while removing said condenser from across said resistor.
4. A microphone amplifier system, comprising a dynamic microphone, a non-dynamic microphone, a grid-controlled amplifier tube for both microphones, said tube having a cathode bias resistor, means including another resistor and a condenser connecting said non-dynamic microphone in series between said cathode and ground, a two-position switch, circuit connections effective in one position of said switch to isolate said non-dynamic microphone from said cathode and simultaneously connecting said condenser in shunt to said bias resistor and other circuit connections effective when said switch is in another position to disconnect said condenser from said bias resistor.
5. A microphone amplifier system, comprising a dynamic microphone, a non-dynamic microphone, a grid-controlled amplifier tube for both microphones, a switch for selectively rendering either of said microphones effective on said amplifier, a cathode bias resistor and shunt condenser for said tube, means effective with the switch in one position to drive the grid of said tube by the output of said dynamic microphone, means effective with the switch in another position to drive the cathode of said tube by the output of said non-dynamic microphone, said switch when in said other position disconnecting said condenser from across said bias resistor.
6. A microphone amplifier system, comprising a pair of microphones of difierent signal outputs, a grid-controlled amplifier tube for both microphones, a bias resistor connected between the cathode of said tube and ground, means connecting one microphone across the grid and ground, a condenser, a two-position switch effective in one position to bridge said bias resistor by said condenser and efiective in another position to disconnect said condenser from across said resistor, and means connecting the other microphone effectively in series with said condenser and cathode when said switch is in said other position.
7. A microphone amplifier system, according to claim 6 in which an adjustable resistor is connected in series between said other microphone and said condenser for equalizing the outputs of the amplifier regardless of which microphone is being used.
WARREN B. BRUENE.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 2,109,756 Sparks Mar. 1, 1938 2,114,019 Friebus Apr. 12, 1938
US8399A 1948-02-14 1948-02-14 Dual microphone system Expired - Lifetime US2490943A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2601271A (en) * 1950-05-20 1952-06-24 Int Standard Electric Corp Direct current stabilizer
US3147345A (en) * 1961-04-26 1964-09-01 Bell Telephone Labor Inc Gain selective telephone set

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2109756A (en) * 1929-06-06 1938-03-01 David E Sparks Electrical amplifying system
US2114019A (en) * 1934-04-26 1938-04-12 Western Electric Co Sound reproducing system

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2109756A (en) * 1929-06-06 1938-03-01 David E Sparks Electrical amplifying system
US2114019A (en) * 1934-04-26 1938-04-12 Western Electric Co Sound reproducing system

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2601271A (en) * 1950-05-20 1952-06-24 Int Standard Electric Corp Direct current stabilizer
US3147345A (en) * 1961-04-26 1964-09-01 Bell Telephone Labor Inc Gain selective telephone set

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