Time constant about a second, about right. A bit hypersensitive with only 2 diode drops DC (1.2 v) setting it off. Utility depends on the power of the amp and the type and rating of the relay contacts. Most relay contacts are AC rated, depending on the zero crossing of the voltage to quench the arc. Large DC currents can weld the contacts together, as the kind you get with dumping the entire content of the rail caps through the shorted output transistor. Many protection boards are sold on e-bay with these *****y undersized relay contacts. Other objection, no latch is included to remember the fault condition and keep the relay open.
The modern version uses drain to drain enhancement nfets in series with the speaker. A fet driver is used to energize the gate as long as everything is okay. See Robert Keene or Bonsai protection threads, although the Bonsai version requires working with surface mount parts.
Suggest you use a seach to find protection threads on this forum. Many circuits have been posted that are better than this one.
The modern version uses drain to drain enhancement nfets in series with the speaker. A fet driver is used to energize the gate as long as everything is okay. See Robert Keene or Bonsai protection threads, although the Bonsai version requires working with surface mount parts.
Suggest you use a seach to find protection threads on this forum. Many circuits have been posted that are better than this one.
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