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phoenix87 17th May 2010 09:43 PM

protection circuit for amps
protection in amps is a very good thing but many dont like them ...... but neways i recently designed a 500W @ 8E amp which is going for the PA use so i would like to use a shortcircuit protection for my amp ...... All u learned people can u help me with this...... Cause a PA amp does nt need to have very good sonics just average sonics with heavy protection is needed.... The protection scheme can be very simple ....


nigelwright7557 17th May 2010 10:18 PM

A VI limiter for shorts, clipping and over driving would be a start.

AndrewT 17th May 2010 10:25 PM

and fuses in the supply rails, although in PA, some form of resettable link would be better. MosFET switch with a timed latch that checks to see if the fault has cleared.
Speaker protection relay and input mute. Both can be used to temporarily shut down before damage gets down.

nigelwright7557 17th May 2010 10:59 PM

I use a PIC micro to monitor the output of my amp and it controls the speaker relay.
It holds off the speaker relay for 3 seconds on power up.
It also monitors b+ and b- for a dc condition for more than 500mS.
Saved me a fortune in speakers !

phoenix87 18th May 2010 05:37 AM

can u post a circuit for a VI limter ............... or some other sort of protection relay cause I already have the DC Detect and the Turn on delay working very properly............


east electronics 18th May 2010 07:51 AM


Originally Posted by AndrewT (
and fuses in the supply rails, although in PA, some form of resettable link would be better. MosFET switch with a timed latch that checks to see if the fault has cleared.
Speaker protection relay and input mute. Both can be used to temporarily shut down before damage gets down.

shuting down in PA bussiness Andrew, is unaxeptable or impossible to happen some time you will have to understand this

everything you do has to happen before amplifier fails or shut down the cost of shuting down will be by far more than a few transistors and some fuse

AndrewT 18th May 2010 09:18 AM

I have been the audience.
I know it's unacceptable to shut down.

But there is a point where the protection will prevent the bad signal passing or a good signal passing to a bad load. That time period must be short. During that time of shutdown, the redundancy in the sound system must cover up the shortfall.
If you cannot hide the shutdown then the audience complains.

east electronics 18th May 2010 09:26 AM

you cannot "hide" a shut down .... probably in mutliway multi speaker system if one goes down only a few will undestand but in a gig that has totally one or two amps ( which is by far most comon than the first case ) then it is going to be way to obvious

indianajo 18th May 2010 01:03 PM

protection ciruit in performance
Sakis, hopefully, for an amp with protection circuits in a performance venue, the speaker shorts and wiring faults are found by the protection circuit in the sound check, and the amplifier shuts down then, leaving the road crew to find the faults with a meter and get everything back running before the actual performance.
I find the cavalier discussion of safe area limiters on custom microprocessors a bit humorous, toys of rich boys. The only way I could afford a VI limiter I know is to buy a blown up Crown or similar professional amp and repair the blown up parts, assuming the microprocessor is not the blown up part. The last catelogs I have, microprocessor development systems are $4000, the emulator umbilacle accessory was $1500, the software development package was $2000. This was for Intel equipment. HP logic analyzers are about $4500. Factory ProgrammableLogicController's are much cheaper in the $300 range but with their 1 bit interface they don't take measurements very well. If you know something better, please spill it.
Until microprocessor development becomes knowable and affordable, the rest of us will have to make do with DC blocking caps in the speaker lines, timer controlled and thermistor controlled speaker relays, speaker fuses, diac-triac speaker shorting assemblies that usually detect blown output transistors, similar second rate solutions. If you look at what someone7272 found, Rapid Electronics - Electrical & Power a packaged protection circuit, I wonder if this is snake oil or if there is some way to communicate amp power on state and VI data to this device. I tried the specifications link on that website and came up with a screen with a tiny logo on it, so I am leaning towards it might be snake oil.

east electronics 18th May 2010 01:18 PM

yet again the same issues the same problems and the same story on trying to make people from a diferent school to understand .....

Indianajo :
I agree to 1000% to what you say the real problem remains very simple .... you need a good machine? then overdesign everything .... big coolers many transitors big supply and so on ....this is not cost effective ....

you need lower cost effective equipment ??? use VI limmiters LDR and all the rest .... OK but they kill your sonics ....

ok then what is the available ways ???
VI limmiters or multislope vi limmiters Ldr protection or combination of both

since for normal class AB ams it seems there is no other way then the trick is to optimize this as much is possible and wait till something more inovative comes arround

only a few days ago i come across a mosfet amplifier that has no VI limmiter only gate stoppers with zeners and so on but has some kind of monitoring on the VAS curent ... i dont know how well it works but someway that is something new at least to me ...

it will be so wonderfull as you say to use Mp monitor voltage and current in all stages of the amplifier and tune all voltage on line and in real time but sounds like space technology to me

the point remains the same good sonics and vi limmiters don go together ....then again pro amps and no VI limmiters also dont go together

so what is the solution ???

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