Low cost of high fidelity high power variable class a amplifier-speaker combination

Claim 2

An amplifier circuit in combination with and connected to a speaker having a voice coil and a speaker cone, comprising: an input amplifier stage for receiving input audio signals; an output amplifier stage having an output terminal directly connected to said voice coil of said speaker and constantly providing a current through said voice coil; capacitive coupling means connected between said input and output stages; current feedback means for direct connection to said voice coil of said speaker and connected to said input stage, said feedback means including a low ohmic resistor connected in series with said voice coil; and bias means connected to said capacitive coupling means and to said output stage for varying the bias on said output stage to allow a very low standby idle current while providing for the transmission of any applied signal whose peak-to-peak value is less than the supply potential, the current constantly provided through said speaker coil and the varying bias and the feedback current providing a linear acoustic response over the working range of said speaker.

Claim 3

The combination according to claim 1, wherein said output stage includes a transistor having a base connected to said capacitive coupling means and said bias means includes a rectifier connected between said base and an electrical supply and operable in response to peaks of the amplified signal to vary the bias and substantially eliminate the distortion ordinarily associated with amplifiers biased nearly to cutoff.

Claim 4

The combination set forth in claim 2, wherein said rectifier includes a diode, and Comprising a voltage divider circuit connected to said diode.

Claim 5

The combination set forth in claim 2, comprising a voltage divider circuit, and wherein said bias means comprises a transistor having a base-collector junction connected between said voltage divider and said base of said output stage transistor.

Claim 6

The combination set forth in claim 1, wherein: said input stage comprises a common emitter amplifier section having an input for receiving audio input signals and for receiving feedback signals and an output connected to said capacitive coupling means; said output stage comprises a Darlington type amplifier section having an input connected to said capacitive coupling means and means including said output terminal and said resistor for establishing a bias current series circuit for said voice coil; and said current feedback means comprises a connection between the junction of said voice coil and said resistor and an impedance connected between said junction and said input of said common emitter amplifier section.

Claim 7

A variable bias class A circuit for reproducing audio signals, in combination comprising: a speaker including a coil and a mechanically suspended speaker cone which is influenced in accordance with the energization of said coil and which has a mechanical rest position when said coil is not energized; a first amplifier stage including an input for receiving the audio input signals and an output for providing amplified audio signals; capacitive coupling means connected to said output of said first amplifier stage; and a second amplifier stage including an input connected to said capacitive coupling means for receiving the amplified audio signals, a variable bias control circuit, and output means for impressing the further amplified audio signals on said speaker coil to cause said speaker cone to vibrate, said output means comprising a direct current series circuit connected between electrical supply potentials and including an output transistor having a collector and an emitter connected in series with said speaker coil and bias means to constantly provide a direct current coil bias which is effective to influence said speaker cone to vibrate about a bias position on one side of its mechanical rest position, said second amplifier stage connected to an electrical supply potential and including means biasing said stage to near cut off, said bias means including a bias varying circuit connected to said capacitive coupling means and to said input of said second amplifier stage and operable to shift the bias on said second amplifier stage for maintaining class A operation in response to signal peaks which approach a level equal to the potential of the electrical supply.

Claim 8

A variable bias class A circuit for reproducing audio signals, in combination comprising: a speaker including a coil and a mechanically suspended speaker cone which is influenced in accordance with the energization of said coil and which has a mechanical rest position when said coil is not energized; a first amplifier stage including an input for receiving the audio input signals and an output for providing amplified audio signals; capacitive coupling means connected to said output of said first amplifier stage; and a second amplifier stage including an input connected to said capacitive coupling means for receiving the amplified audio signals, a variable bias control circuit, and output means for impressing the further amplified audio signals on said speaker coil to cause said speaker cone to vibrate, said output means comprising a direct current series circuit connected between electrical supply potentials and including an output transistor having a collector and an emitter connected in series with said speaker coil and bias means to constantly provide a direct current coil bias which is effective to influence said speaker cone to vibrate about a bias position on one side of its mechanical rest position, said second amplifier stage connected to an electrical supply potential and including means biasing said stage to near cut off, said bias means including a bias varying circuit connected to said capacitive coupling means and to said input of said second amplifier stage and operable to shift the bias on said second amplifier stage for maintaining class A operation in response to signal peaks which approach a level equal to the potential of the electrical supply.