[Radio Wrangler]

In general, do not disconnect speakers, whether by pulling plugs, external switches or even by switches built into amplifiers while the amplifier is on.

As Lucien says, the break of a circuit with current flowing into an inductive load will create a spark at the switch and send a voltage transient backwards into the amplifier.

Many amplifiers are built with some degree of protection against this, many amplifiers are not. Those catching diodes cost pennies at the prices manufacturers pay, so in consumer amps, there is an incentive to not bother. Some boutique amplifiers eschew them on grounds that they will do imagined damage to the sound and reduce the niceness of the adjectives which reviewers will use. Even in amplifiers with some protection, they often haven't used fast enough diodes to catch all such transients reliably.

So there is a risk. Even with a fairly well-protected amplifier, the risk isn't quite driven down to zero. Lucien works with amplifiers designed for a stage environment where speaker connections get mucked about with regularly. Their protection has to be excellent they need things to be reliable.

So, even with a domestic hifi amp with a speaker switch on the front panel, don't change the switch with the amp on. Assume that the protection from speaker circuit transients won't always save you. It's statistical. You'll probably get away with it, but that one exception in a large number of occasions will eventually leave you with a dead amplifier.

Have a look through the forum and you'll find lots of transistor amps with failed output transistors and some damage further back into them. You'll also find that these repairs are difficult and don't always go well. You'll find that getting the right transistors can be difficult.

So, those blown amplifiers.... did they fall, or were they pushed?

This area is one of the major risk factors. A lot of people get away with it, but then not every time. Voltage transient overstress can do cumulative damage leading to eventual failure.

"How lucky do you feel?" as Mr Eastwood asked.

David