Surges and spikes

Firstly, spikes and surges mean the same thing - basically spikes lasting less than a thousandth of a second. These are due to static and other forms of energy release (thunder storms, energy being released by transmitter spark gaps - even some old high powered valve amps had spark gaps, inductive items like motors, central heating solenoids, fridge compressors etc switching off).

They can exist on the mains/line supply and under some circumstances some equipment can be destroyed internally. In a thunder storm a wireless router can receive a spike that exceeds RF transistor voltage rating, causing it to fail. Such a device is a "fast circuit" (my description) which has no form of passive protection to "slow down" such short transitions because, otherwise, they would not be able to do their proper job of dealing with radio frequencies.

Generally, audio equipment has input and output capacitance which can take the form of real capacitors, and often there is series resistance. Going straight from the outside world into an active device's input (or output) shows a fault in the designer as well as the design. Capacitance and series resistance are absorbers of spikes, and mostly they are survivors of spikes within limits. Mainly things survive.

Power inputs (and all ins and outs) suffering direct strikes would not survive, but neither would the occupant...

Often, a strike will be onto the mains/line transport. Pylon construction encourages lightning to hit the pylon itself using highly conductive heavy duty conductors to earth, and the inslulators on the hangers are designed to "dilute" the energy transfered to the suppy cables - but some gets through.

The inline fuse of a mains/line circuit in overload condition will heat up, and resist the energy in the spike, and mainly they survive, all these things tend to serve to limit the eventual size of spike reaching the equipment, but some can reach it. At this moment in time 8kV (8,000V) lasting 1 nano second, and a 50% decay lasting 60 nano seconds must be survivable.

The transformer in equipment power supplies has a very poor frequency response, so energy passing it will use its winding capacitance to find its way in. The rectifier and reservoir capacitor present a load to that capacitance and can have an attenuating effect, reducing the spike further.

The DC input of a remote supply product often has a series inductor followed by a filter capacitor which is often fast enough to catch some of the spike, and they can usually survive the voltage. It is then up to the circuits' devices to resist the residue. If by design a pulse can set up oscillation the energy isn't lost immediately and if the device voltage rating isn't sufficiently high, damage could occur (this could be why the amp manufacturer says to unplug the item when not in use).

Nothing is perfect, and things do fail, but taking stock of all the things that help protect our circuits, and going on their longevity so far, most of them having been on all the time through static storms, none have failed yet to my knowledge, but being real about it, one day it could happen.

More legislation from Europe now requires further circuit protection from spikes, and although it will take time to redo circuit boards, our products will feature further protection as prescribed (actually the word prescribed is probably the wrong word to use because they don't tell you how to do it - they just tell you to do it - and the solution has to come from the designers' capabilities).

The new phono stage will be the first of our products to carry all the features required for ESD (spikes) and EMC that the new stricter standards being brought out in 2016 demand.

I live in a rural area where all our grid power feeds are overhead lines, almost all in elevated open countryside. Quite often during electrical storms we experience short brown outs, co-incident with lightning flashes, which I assume are due to the HV surge protection operating. Despite these events I've only ever had one instance of equipment being affected by an electrical storm. An adjacent property suffered a lightning strike and my early Pure DAB receiver with dedicated roof mounted aerial lost some functionality. Unfortunately our neighbours' TV, booster and aerial didn't survive, the aerial, cable and TV sockets also suffered severe burning. Fortunately, they were out at the time.
Consequently, I wouldn't really worry about surges and spikes, excepting a direct hit it seems that the protection devices do their job.