Audiolab DCBLOCKS Block Audio Grade Mains Filter and Direct Current Blocker - SilverThe typical mains supply is subject to various kinds of interference and non linear loads, which distorts the AC waveform. Asymmetrical loads will cause the waveform to be offset and result in what is known as 'DC on the mains'. The amount of DC is only small, typically less than 500mV, but it only takes a small amount of DC to saturate a modern high flux toroidal transformer. Saturation of the transformer will invariably result in reduced efficiency