Dave Plowman (News) wrote:



** Speaker muting relays have been standard features in countless home
and professional audio amplifiers for decades. Their main purpose is to
stop transients at switch on/off from being heard.


They can also include a circuit to make them drop out if they detect a
large DC offset. Very good way of protecting speakers in event of a fault.



** Few speaker relay systems provide reliable protection if that happens - nor do they claim to.

The simple fact being that the kind of relays used are only capable of switching *off* DC voltages to a maximum of 30V at rated current. IOW, their current breaking capacity is very limited for DC voltages.

What happens instead is a continuous arc forms between the contacts as they open and persists until the relay is destroyed along with the speaker voice coil as well.

Amplifiers with DC supply rails under 50V may allow the arc to break, but any higher and there is practically no chance.



.... Phil