Feedback amplifier and audio system thererof

A feedback amplifier comprising:

• an operational amplifier comprising an input end and an output end;
• a first resistor having a first resistance (R1) and being coupled with the input end of the operational amplifier;
• a second resistor having a second resistance (R2), the second resistor having a first end coupled with the input end of the operational amplifier and a second end coupled with the output end of the amplifier;
• and
• a voltage divider having a first end being operably coupled with the output end of the operational amplifier and a second end operably coupled with an analog ground, the voltage divider including a third resistance (R3) and a fourth resistance (R4), wherein the feedback amplifier provides a gain of about 20*log(R2/R1)+20*log(R4/(R3+R4)).

An audio system comprising:

• a speaker;
• and
• a feedback amplifier coupled to the speaker, the feedback amplifier including:
• an operational amplifier comprising an input end and an output end, the output end being coupled with the speaker;
• a first resistor coupled with the input end of the operational amplifier;
• a second resistor having a first end coupled with the input end of the operational amplifier and a second end coupled with the output end of the amplifier;
• a voltage divider having a first end being operably coupled with the output end of the operational amplifier and a second end being analog grounded;
• a first switch coupled to the first end of the voltage divider with the output end of the operational amplifier;
• and
• a second switch coupling the output end of the operational amplifier with a node in the voltage divider between the first end and the second end of the voltage divider to divide the resistance of the voltage divider into a third resistance (R3) and a fourth resistance (R4).