wrote:

The horn is DC coupled ? Why the hell would they do that ?

** Most are like that and a real lot have LM3886 amps driving the horn direct.


I was on audiokarma the other day and someone mentioned a protect circuit that wa powered by the DC from the amp. Not hard to figure out how it works, it is a matter of finding a relay, normally closed of course, that will activate at a low enough voltage and current. Couple resistors going to a bridge and a filter should do it.

** The relay MUST short the speaker to protect it and that means the contacts are normally open. Since the coil is not polarity sensitive, there is no need for bridge - just some RC filtering and a fuse on the amp side.


Another thing was about the magnets on the sides of the relay, remember that thread ? you said that it was to draw the arc away from betweent the point so they would be less likely to weld themselves together due to the inductive CEMF.

** Nope, it is to help break the arc that forms when contact open under heavy DC current and voltage. 40V and 5 amps are the limit for most small AC rated relays - adding a suitable magnet might increase that to 50V and 10 amps.


I posted that a cap, like a 10 uF or whatever, across the cntacts should work just fine.

** No it wont.


.... Phil