Muting system for power amplifier

Claim 2

A power amplifier comprising a pre-amplifier portion connected to an amplifier portion having a push-pull amplifier configuration and a voltage gain of substantially unity, a D.C. feedback path connecting the mid-point output of the push-pull amplifier portion to said pre-amplifier portion, and muting means connected to the push-pull amplifier portion for controlling the mid-point output potential of said push-pull amplifier portion to block input signals in said pre-amplifier portion via said D.C. feedback path.

Claim 3

A power amplifier as defined in claim 1, wherein said muting means comprises a resistance element and a switch connected in series between a signal path of said push-pull amplifier portion and one side of a potential source, and a capacitor connected in parallel with said switch.

Claim 4

A power amplifier as defined in claim 2, wherein said amplifier portion includes first and second transistors connected in A Darlington configuration to form a first stage, third and fourth transistors connected in a Darlington configuration to form a second stage which is connected in a push-pull amplifier configuration to said first stage to form a mid-point output.

Claim 5

A power amplifier as defined in claim 3, wherein said muting means is connected to the control electrode of one of said first and second transistors.

Claim 6

A power amplifier as defined in claim 3 wherein said muting means is connected to the control electrode of one of said third and fourth transistors.

Claim 7

A power amplifier as defined in claim 3, further including a further resistance element having a tap, at least one diode and a fifth transistor connected in series across said potential source, the input of said first stage being connected between said further resistance element and said one diode and the input of said second stage being connected between said one diode and said fifth transistor, the control electrode of said fifth transistor being connected to the output of said pre-amplifier portion and said muting means being connected to the tap of said further resistance element.

Claim 8

A power amplifier as defined in claim 2, wherein said amplifier portion includes first and second amplifier stages connected together in push-pull amplifier configuration to form a mid-point output, said muting means being connected to the input to one of said first and second stages.

Claim 9

A power amplifier comprising a pre-amplifier including a first transistor and a second transistor connected to form a differential amplifier, a power amplifier including first and second transistor means connected to each other in push-pull configuration and having a voltage gain of substantially unity, an output terminal connected to the connection point between said first and second transistor means of said power amplifier, means connected between an output electrode of said second transistor of said pre-amplifier and an input of said push-pull amplifier for transmitting an output signal from said pre-amplifier to the input of said power amplifier, feed-back means connected between said output terminal and an input electrode of said second transistor of said pre-amplifier for feeding back the output signal of said power amplifier to said preamplifier, means connected to an input electrode of said first transistor of said pre-amplifier for applying an input signal to said pre-amplifier, and muting means including a mechanical switch connected to the input of said power amplifier for causing a voltage change at said output terminal sufficient to turn-off said second transistor of the pre-amplifier upon closure of said mechanical switch, the voltage change caused at the output of said power amplifier being transferred to the input electrode of said second transistor of the pre-amplifier through said feed-back means, resulting in a turning-off of said second transistor of the pre-amplifier thereby to block an input signal from being transmitted from the pre-amplifier to the power amplifier.

Claim 10

A power amplifier comprising a pre-amplifier including a first transistor and a second transistor connected to form a differential amplifier, a power amplifier including first and second transistor means connected to each other in push-pull configuration and having a voltage gain of substantially unity, an output terminal connected to the connection point between said first and second transistor means of said power amplifier, means connected between an output electrode of said second transistor of said pre-amplifier and an input of said push-pull amplifier for transmitting an output signal from said pre-amplifier to the input of said power amplifier, feed-back means connected between said output terminal and an input electrode of said second transistor of said pre-amplifier for feeding back the output signal of said power amplifier to said preamplifier, means connected to an input electrode of said first transistor of said pre-amplifier for applying an input signal to said pre-amplifier, and muting means including a mechanical switch connected to the input of said power amplifier for causing a voltage change at said output terminal sufficient to turn-off said second transistor of the pre-amplifier upon closure of said mechanical switch, the voltage change caused at the output of said power amplifier being transferred to the input electrode of said second transistor of the pre-amplifier through said feed-back means, resulting in a turning-off of said second transistor of the pre-amplifier thereby to block an input signal from being transmitted from the pre-amplifier to the power amplifier.