An electronic device such as a handheld electronic device may include wireless communications circuitry. The wireless communications circuitry may include a radio-frequency receiver circuit or other circuitry that is sensitive to noise. Audio amplifier circuitry may be provided in the electronic device to amplify audio signals for a speaker. The audio amplifier circuitry may include class AB amplifier circuitry for operating in a low noise mode and class D amplifier circuitry for operating in a low power mode. The audio amplifier circuitry may include a control input path that receives control signals in real time. When it is determined that the wireless receiver or other sensitive circuit is active, the audio amplifier can be configured to operate in its low noise mode using the class AB amplifier. When it is determine that the wireless receiver is not being used, the class D circuitry may be switched into use to conserve power.