Certain aspects of the present disclosure are generally directed to circuitry and techniques for adjusting an audio signal to avoid undesirable system behavior under low alternating-current (AC) line voltage and high volume conditions. For example, certain aspects provide an apparatus for audio amplification. The apparatus generally includes an amplifier, a supply voltage generation circuit having an input coupled to an input voltage node of the apparatus and an output coupled to a supply voltage terminal of the amplifier, the supply voltage generation circuit having a transformer, a primary winding of the transformer being coupled to the input voltage node, a peak voltage detector circuit configured to detect a peak voltage at a secondary winding of the transformer, and a controller circuit configured to adjust an input audio signal of the amplifier based on the detected peak voltage.