An ultimate amp protection circuit ?

[Esperado]

has anyone tested THD of the back to back mosfets as well as their ability to withstand a 0.22 ohm short to one of the rails. fets usually die shorted not open

About THD, with the ones we had chosen, very low RDS on, negligible, omho.
About the risk of blowing them, i have serious doubt, if we consider how fast this protection will cut them (µs). No time to heat. And, if you really worry, use mechanical ones in //.

 

[jwilhelm]

I've used Esperado's design of Mosfet relay in a few amps I've built. Before putting the design into service, I purposely tuned a spare test amp to oscillate and explode into a 4 ohm dummy load to see how the relays would fare. Both mosfets blew open, not shorted. This was with IPB025N-10N3 mosfets.

 

[andrewlebon]

Hello Esperado
greetings can you share schematic with reset button i would like
to try it
warm regards
Andrew

 

[Esperado]

Here a version with a reset button (not verified).
The speakers are connected 7 second after power on. In case of trouble, the protection will fire and not be rearmed until or a restart of the amplifier, or a push on a "reset" button.
(Beware, I forgot to set a 1K resistor between Q out and the base of the transistor and, of course, the diode across the relay !).

 

[Esperado]

And, to satisfy LineSource's request, a version with independent dual inputs.
The strap allows the protection to stay fired until "reset" is pushed, while, when strap is not in place, the protection will automatically rearm 7s after the source of the problem had stopped.
It use a quad OPA + a LM339.
Like all the versions, the circuit will connect your speakers (if nothing wrong) only 7s after power on. And will disconnect when power-off, making those power operations absolutly silent in daily use.
Chose your poison ;-)

 

[rensli]

Great work on the project !

I have an idea to replace my protection circuitry for this one.
Currently i use Chinese UPC1237 protection with one dual contact relay for both channels. It works from ("or detects" 3V DC) and you are even able to actually count numbers before it disconnects the speakers... Heat up is guaranteed... so, if something goes wrong and +/-41V DC shows up with the 500VA transformer rating on speaker output terminals... then there will be two possible consequence's:

Welded relay contacts or completely blown speaker protection board. The last is what i hope will happen to save speakers..

Will there be a group buy ? I am interested on two PCB boards..
Esperado or Alex will share PCB files ?

 

[kpsthakur]

Gentlemen are there any Gerber files for this, went from 1st comment till last, awesome info and theory, would definitely like to have one for my 400W amp.

 

[Angelsword]

Hello Esperado
greetings just want to ask you when i short speaker wires protection
kicks but relay goes on off i think flip flop circuit needed for relay
whats your views i will post video to show you
warm regards
Andrew

Hi !

Sorry to bring up this topic but it is very interesting.

I had the same problem as you, I believe there is an error on the reverse input of the 4th OPA.

You have put a resistor of 1M and another of 4K so that you do not have the timing of 2 seconds for the relay, you have to put a resistor of 2M and 2K as Esperado says and it works, the relay takes 2 seconds to recover from the problem.

Sorry for my bad English I am French.