Audio limiter using voltage multiplexed feedback

• US 4,978,926 A
• Filed: 12/21/1989
• Issued: 12/18/1990
• Est. Priority Date: 12/21/1989
• Status: Expired due to Term

• Current Assignee: Visteon Global Technologies Incorporated (Visteon Corporation)
• Original Assignee: Ford Motor Company
• Inventors: Zerod, Richard D., Hamel, Gregory R.
• Primary Examiner(s): MOTTOLA, STEVEN J
• Application Number:
  US07/454,601
• Time in Patent Office: 362 Days
• Field of Search: 330/51, 330/129, 330/133, 330/135, 330/149, 330/278, 330/279, 330/284, 455/174
• US Class Current: 330/279
• CPC Class Codes: H03G 3/3026 the gain being discontinuously variable, e.g. controlled by switching
• CPC Class Codes: H03G 3/34 Muting amplifier when no signal is present or when only weak signals are present, or caused by the presence of noise signals, e.g. squelch systems

Abstract

An audio system having a main chassis including an audio preamplifier and a remote chassis including a power amplifier has a clipping level detector circuit in the remote chassis for detecting the onset of clipping by the power amplifier and has a gain control element in the main chassis for controlling the gain of the preamplifier. An extra control line in the wiring harness connecting the main chassis and the remote chassis is avoided by multiplexing the clipping signal and the mute control signal on a single control wire.

Claims

1. An audio system for amplifying an audio signal comprising:

a main chassis;

a remote amplifier stage;

a mute control line coupling said main chassis and said remote amplifier stage; and

at least one audio line coupling said audio signal from said main chassis to said remote amplifier stage;

said main chassis including;

preamplifier means for amplifying said

audio signal;

mute control means coupled to said mute control line for driving said mute control line with a first voltage to cause a muted state of said audio system and for driving said mute control line with a second voltage to cause an unmuted state of said audio system;

voltage comparator means coupled to said mute control line for comparing a voltage present on said mute control line with a reference voltage and generating a gain reduction signal depending on the result of said comparison; and

gain control means coupled to said preamplifier means and to said voltage comparator means for reducing the magnitude of said audio signal at the output of said preamplifier means in response to said gain reduction signal;

said remote amplifier stage including;

power amplifier means coupled to said preamplifier means for amplifying said audio signal by a substantially fixed gain;

amplifier muting means coupled to said power amplifier means and to said mute control line for muting an audio output of said power amplifier means in response to said first voltage being present on said mute control line; and

clip detector means coupled to said power amplifier means and said mute control line for driving said mute control line with a third voltage whenever said fixed gain amplification of said audio signal results in signal clipping, said reference voltage having a magnitude between said second and third voltages.

2. The system of claim 1 wherein said second voltage has a magnitude between said first and third voltages.

3. The system of claim 1 wherein said gain control means includes means for variably attenuating said audio signal input to said preamplifier means in response to said gain reduction signal.

4. The system of claim 1 further comprising a program source for generating said audio signal.

5. The system of claim 1 further comprising an output speaker coupled to said power amplifier means.

6. A method of preventing distortion in an audio system including a preamplifier on a main chassis providing an audio signal to a remote amplifier stage, said method comprising the steps of:

providing conduction path means for defining a single conduction path between said main chassis and said remote amplifier stage;

generating a clip signal upon the onset of clipping in said remote amplifier stage;

controlling the output of said remote amplifier stage from said main chassis by means of a mute control signal applied to said conduction path means from said main chassis to said remote amplifier stage;

multiplexing said clip signal and said mute control signal on said conduction path means to communicate the onset of clipping to said main chassis; and

reducing the magnitude of said audio signal at the output of said preamplifier in response to said clip signal, whereby clipping in said remote amplifier is prevented.

7. The method of claim 6 wherein said clip signal is represented by a first voltage being applied to said conduction path means and wherein said mute control signal is represented by a second voltage being applied to said conduction path means.