US3595998A - Polarity independent preamplifier for sound transmitters - Google Patents

Polarity independent preamplifier for sound transmitters Download PDF

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Publication number
US3595998A
US3595998A US838091A US3595998DA US3595998A US 3595998 A US3595998 A US 3595998A US 838091 A US838091 A US 838091A US 3595998D A US3595998D A US 3595998DA US 3595998 A US3595998 A US 3595998A
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Prior art keywords
potential
output
voltage
circuit
input terminal
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Expired - Lifetime
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US838091A
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English (en)
Inventor
Werner Fidi
Bernhard Weingartner
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AKG Acoustics GmbH
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AKG Akustische und Kino Geraete GmbH
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/181—Low-frequency amplifiers, e.g. audio preamplifiers
    • H03F3/183—Low-frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only
    • H03F3/185—Low-frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only with field-effect devices

Definitions

  • ABSTRACT A preamplifier for sound transmitters includes at least one field effect transistor having a gate electrode and first and second output electrodes An output circuit is connected across the output electrodes, a first output electrode resistor is connected between a feed voltage input terminal and the first output electrode and a second output electrode resistor is connected between a reference potential terminal and the second output electrode.
  • the output electrode resistors have substantially the same resistance.
  • a polarity dependent biasing circuit is connected between the feed voltage input terminal and the gate electrode, and maintains, at the gate, substantially a predetermined negative bias potential relative to the potential at the first output electrode if a potential which is negative by a predetermined amount relative to the potential at the reference potential terminal is applied to the feed voltage input terminal, and relative to the potential at the second output electrode if a potential which is positive by the predetermined amount relative to the potential at the reference potential terminal is applied to the feed voltage input terminal.
  • a phantom circuit may be used to supply the feed voltage to the preamplifier.
  • the two sound conductors are used as outgoing conductors and the shield of the cable serves as a return conductor.
  • the third conductor may be used instead of the shielding sheath.
  • the amplifiers may be provided with PNP transistors (the positive terminal of the feed voltage source is grounded) or with NPN transistors (the negative terminal of the feed voltage source is grounded), so that damage may be caused by a wrong polarity connection.
  • This invention relates to preamplifiers for sound transmitters, preferably for capacitive transducers, and more particularly, to a preamplifier including at least one field effect transistor and which is bipolar with respect to the polarity of the feed voltage source.
  • a preamplifier which is bipolar with respect to the polarity of the feed voltage source is provided, so that it can be operated with a grounded negative terminal or with a grounded positive terminal without any necessity of a changeover.
  • the invention is based on the concept of utilizing the symmetrical properties of a field effect transistor, and on using special circuitry to produce a gate bias which depends on the polarity of the feed voltage, so that the gate bias of the field effect transistor will be properly set irrespective of the polarity of the feed voltage supplied thereto.
  • An object of the invention is to provide an improved preamplifier for sound transmitters.
  • Another object of the invention is to provide such a preamplifier including at least one field effect transistor.
  • a further object ofthe invention is to provide a preamplifier which is free of disadvantages of prior art transistorized preamplifiers.
  • Another object of the invention is to provide a preamplifier which is bipolar with respect to the polarity ofthe feed voltage source.
  • a further object of the invention is to provide a preamplifier utilizing the symmetrical properties of the field effect transistor.
  • Another object of the invention is to provide a preamplifier in which the gate bias of the field effect preamplifier will be properly set irrespective of the polarity of the field voltage supplied thereto.
  • FIGS. 1 and 2 are schematic wiring diagrams illustrating two different exemplary embodiments of the invention.
  • FIG. 1 shows the circuit of the preamplifier, according to the invention, in combination with a condenser microphone M.
  • the latter is supplied with a polarizing voltage U through a series resistor R,..
  • the nongrounded electrode of condenser microphone M is connected by a coupling capacitor C to the gate electrode 3 of a field effect transistor.
  • the two other, or output, electrodes of the transistor are connected by coupling capacitors C to the primary winding of an output transformer Tr.
  • a resistor R connects electrode 2 to one terminal tu of the feed voltage source.
  • Electrode I is connected by resistor R to the reference line. According to the invention, the two resistors R and R have at least approximately the same resistance.
  • a voltage divider comprising resistors R,, R is directly connected to the feed voltage between terminal :U,, and the reference line.
  • the tap of the voltage divider is connected by a resistor R,,., having preferably a high resistance, to gate electrode 3 to bias the latter.
  • An auxiliary circuit comprising a diode D in series with a resistor R is connected in parallel to resistor R of the voltage divider.
  • this auxiliary circuit renders the voltage divider, connected across the feed voltage, dependent on polarity. Depending on the polarity of the feed voltage, the same is divided by the voltage divider according to the ratio R :(R +R or the ratio R R /R +R :(R, -l-R R lR +R so that the bias of the gate electrode is changed in dependence on the mode of operation of the field effect transistor.
  • the polarity of the feed voltage is such that diode D is blocked so that resistor R does not shunt resistor R
  • resistor R will directly shunt resistor R if the resistance of the diode is neglected, so that the gate bias voltage is lower than the voltage at electrode 1. This will be the case if a positive voltage is applied to the terminal iU The field effect transistor will then be used in its normal circuit, where electrode 1 is the source and electrode 2 the drain electrode.
  • electrode 2 acts as a source electrode and electrode 1 as a drain electrode. Because a negative voltage is applied to diode D, this diode is blocked and the voltage applied to gate electrode 3 is raised, so that the bias between electrodes 3 and 2 is the same as that applied between electrodes 3 and 1 when the feed voltage had the opposite polarity.
  • the circuit shown in FIG. 2 differs from that of FIG. 1 in that a fixed voltage source U,,, rather than diode D, is connected in the auxiliary circuit.
  • Voltage source U may comprise, e.g., a battery.
  • the auxiliary circuit consists of voltage source U connected in series with resistor R Resistor R is a common constituent of the auxiliary circuit and of the voltage divider circuit.
  • the bias voltage for gate electrode 3 of the field effect transistor is developed across resistor R Depending on the polarity of feed voltage U,,, the current flowing through resistor R;, will be either increased or reduced, so that the proper bias voltage will be applied to gate electrode 3.
  • This bias voltage is designated U in FIG. 2 and can be calculated as U R3((/
  • the circuit, shown in FIG. 2, of a bipolar preamplifier for sound transmitters, preferably capacitive transducers, has the same properties as the circuit shown in FIG. 1, in that the feed voltage can be applied regardless of its polarity.
  • a preamplifier according to the invention may be supplied with feed voltage from a power amplifier or the like provided with PNP transistors or with NPN transistors, and may be connected without need for special attention, with one type being sufficient for all cases.
  • a preamplifier circuit arrangement comprising at least one field effect transistor having first and second output electrodes and a gate electrode; means providing a low impedance path connecting said gate electrode said sound transmitter; a feed voltage input terminal; a reference potential terminal; an output circuit connected across said first and second output electrodes; a first output electrode resistor connected between said feed voltage input terminal and said first output electrode; a second output electrode resistor connected between said reference potential terminal and said second output electrode; said first and second output electrode resistors having substantially the same resistance; and a polarity dependent biasing circuit con nected between said feed voltage input terminal and said gate electrode, said polarity dependent biasing circuit maintaining,
  • substantially a predetermined negative bias potential relative to the potential at said first output electrode if a potential which is negative by a predetermined amount relative to the potential at said reference potential ter minal is applied to said feed voltage input terminal, or relative to the potential at said second output electrode if a potential which is positive by said predetermined amount relative to the potential at said reference potential terminal is applied to said feed voltage input terminal.
  • biasing circuit comprises a polarity dependent voltage divider arranged to divide a direct current voltage, applied thereacross, in different ratios in dependence on the polarity of said direct current voltage.
  • said biasing circuit comprises an auxiliary voltage source; a first deriving circuit deriving first direct current voltage from said auxiliary voltage source; a second deriving circuit deriving a second circuit current voltage from the potential applied to said feed voltage input terminal; and a combining circuit superimposing said first and second direct current voltages and applying the resulting voltage to said gate electrode.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
US838091A 1968-07-05 1969-07-01 Polarity independent preamplifier for sound transmitters Expired - Lifetime US3595998A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
AT652068A AT287814B (de) 1968-07-05 1968-07-05 Vorverstärker für Schallempfänger, insbesondere für kapazitive Wandler

Publications (1)

Publication Number Publication Date
US3595998A true US3595998A (en) 1971-07-27

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US838091A Expired - Lifetime US3595998A (en) 1968-07-05 1969-07-01 Polarity independent preamplifier for sound transmitters

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US (1) US3595998A (de)
AT (1) AT287814B (de)
DE (1) DE1930676A1 (de)
GB (1) GB1261070A (de)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3706852A (en) * 1971-01-04 1972-12-19 Mc Graw Edison Co Quiet turn-on circuit for carbon microphones
US4774477A (en) * 1987-03-18 1988-09-27 Rockwell International Corporation Power amplifier having low intermodulation distortion
US5097224A (en) * 1991-04-11 1992-03-17 Telex Communications, Inc. Self-biasing, low noise amplifier of extended dynamic range
WO2002078177A1 (de) * 2001-03-26 2002-10-03 Georg Neumann Gmbh Verstärkerschaltung
US6577187B1 (en) 2000-06-15 2003-06-10 Upstate Audio Powered transducer preamplifier with DC level shifting circuit
US20040196990A1 (en) * 2003-01-15 2004-10-07 Kabushiki Kaisha Audio-Technica Phantom powered capacitor microphone and a method of using a vacuum tube in the same

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3706852A (en) * 1971-01-04 1972-12-19 Mc Graw Edison Co Quiet turn-on circuit for carbon microphones
US4774477A (en) * 1987-03-18 1988-09-27 Rockwell International Corporation Power amplifier having low intermodulation distortion
EP0283143A3 (en) * 1987-03-18 1989-03-08 Rockwell International Corporation Power amplifier having low intermodulation distortion
US5097224A (en) * 1991-04-11 1992-03-17 Telex Communications, Inc. Self-biasing, low noise amplifier of extended dynamic range
US6577187B1 (en) 2000-06-15 2003-06-10 Upstate Audio Powered transducer preamplifier with DC level shifting circuit
WO2002078177A1 (de) * 2001-03-26 2002-10-03 Georg Neumann Gmbh Verstärkerschaltung
US20040131210A1 (en) * 2001-03-26 2004-07-08 Otmar Kern Amplifying circuit
US6812788B2 (en) 2001-03-26 2004-11-02 Georg Neumann Gmbh Amplifying circuit
US20040196990A1 (en) * 2003-01-15 2004-10-07 Kabushiki Kaisha Audio-Technica Phantom powered capacitor microphone and a method of using a vacuum tube in the same
US7295675B2 (en) * 2003-01-15 2007-11-13 Kabushiki Kaisha Audio-Technica Phantom powered capacitor microphone and a method of using a vacuum tube in the same

Also Published As

Publication number Publication date
GB1261070A (en) 1972-01-19
AT287814B (de) 1971-02-10
DE1930676A1 (de) 1970-01-08

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