As identified by Russ Andrews over 15 years ago, such a plethora or train of 'fast' spikes (on or induced from, the AC supply) may be invisible to all but the most specialised measurement setups, yet able to create audio- band noise in audio equipment.This is naturally most (but not exclusively) evident in higher quality equipment having low self-noise.The noise created by RF and RF EMI such as fast spike trains, may be perceived only subliminally, yet is capable of smothering musical detail, or of adding a disturbing quality or edge.This in part is because spikes can also result in slew-limiting - that then affects biasing and so alters or raises audio distortion, both the latter for periods extended vastly past a single spike's own duration (see below).
Removing RF noise impulses, or preventing their worst effects, is one of the 'duty areas' that Zobel networks excel at. In this context or guise, they may be said to be snubbing.The keynote is extra loading and dissipation of edges and impulsive energy.The RF is 'burnt away' - got rid of as heat. This is part of the 'zap' concept: the RF can't spring back.The relevance is that with filters, which mainly depend on L-C networks, it can return. Or, cause problems elsewhere. As the usual kinds of filter (made for brute power efficiency without any other perspective) have often only really 'batted the unwanted energy away', with the blithe assumption - or open- ended hope - that the energy will 'go hang' elsewhere. But with the Zobel, the energy gets transformed into heat. Figure 2 below shows the Zapperator's 'spike eating' reduces a 1ns spike-train's amplitude by
© November 2009 Ben Duncan Research - UK & Russ Andrews Accessories Ltd
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