Mains electricity has a fundamental influence on the audio signal as it passes through a system, from source to amp to speakers. The mains supply in a typical dwelling is subject to interference induced by a range of issues, causing the AC waveform to distort before it reaches each component. This creates noise in the audio signal, which degrades sound quality – a situation that continues to worsen as the electrical devices we use in our homes proliferate.

One common issue is ‘DC on the mains’ – a problem well known to affect the performance of audio equipment, especially amplifiers. In theory, the mains electricity we obtain from the sockets in our homes should be pure AC, with a perfectly symmetrical sine wave alternating between positive and negative phases. However, the presence of ‘asymmetrical loads’ – myriad household devices that use the AC energy available in the mains cycle unevenly, from dimmer switches to kitchen appliances to computer power supplies – causes the waveform to become offset, resulting in the presence of DC voltage on the AC supply.

The AC transformers commonly used in home audio equipment cannot tolerate the presence of significant levels of DC voltage without being compromised. Less than 500mV of DC – typical in an average household electricity supply – can be sufficient to cause toroidal transformers of the kind often found in amplifiers to become saturated, which adversely affects sonic performance and may cause audible mechanical vibration.

By blocking, or canceling, DC voltage found within the AC mains supply, the Audiolab DC Block corrects the DC offset and rebalances the mains sine wave (see illustration above). But tackling ‘DC on the mains’ is not the only benefit delivered by this dual-action device – it also contains a high-performance audio class filtering circuit that removes RFI/EMI contaminants from the mains supply. This is effective in reducing both differential-mode noise (exacerbated by cheap switch-mode power supplies used by many home appliances) and common-mode noise (aggravated by airborne interference from phones, Wi-Fi networks, and Bluetooth).