Noise on the mains, cause?

Discussion in 'Electricians' Talk' started by Hans_25, Jul 6, 2021.

  1. MGW

    MGW Screwfix Select

    I would test by running from an inverter, if noise still there then RF not mains, no point in filters if there is nothing to filter.

    But I had both my parents audio systems plus my own, and reasonably large speakers, but I have a problem in that radio needs aerials in this part of Wales, so we got Nest Mini to get radio through internet, so had two options satellite or Nest for Radio and could not hear the difference, so got rid of large audio systems, one big advantage is no wires to join the two Nest speakers so the speaker wires don't pick up interference as they don't exist.

    Unless setting up a dedicated room for HiFi one simply does not sit in ideal place, or blank out noise from outside, so there is a limit to what is worth while to get good sound.
  2. Bob Rathbone

    Bob Rathbone Screwfix Select

    The HF noise on the mains, or 'Spikes' will not pass through the HV transformer as the impedance of the windings will present a high 'resistance' to them and little current flow will be caused in the primary by these events. The real culprits are switching power supplies and motor controllers, the obvious 'chopping up' of DC to create a quasi AC causes lots of sharp edges on the wave form with fast rise times, these are the high frequency events that cause the problems. We should not forget the humble rectifier, the full wave bridge or Bi phase rectifier. The silicon diodes in these do not turn on until 0.6V appears across them, then a sudden turn on occurs. This causes switching transients that are sometimes reduced, but not eliminated by small capacitors connected across each diode.

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