Fast blow AGC fuses vs polyswitches

[speakerdoctor]

Which is better for speaker driver protection?

[wolf_teeth]

Originally Posted by speakerdoctor

Which is better for speaker driver protection?

If you don't want any incresaed series resistance, use the fast-blow. The Polyswitches, IME, have about 1 ohm added DCR to your signal chain.

Recommendation: Whichever you choose, place a 15 ohm resistor in parallel with it so you know the driver protected is okay. It will just be a lot lower in output level.

Later,
Wolf

[Mooly]

Originally Posted by speakerdoctor

Which is better for speaker driver protection?

As above... the fuse is best.

It all really depends what you are protecting against.

DC offset ? A small offset can cause a significant current which can overheat and burn out a driver. It's unlikely as most DC faults cause a full rail voltage to appear but it can happen. In either event a fuse may not provide enough protection depending on its value and the speaker itself. So DC offset protection is recommended.

Overload due to excessive volume ? A fuse is fine, particularly if the amp never clips.

[wintermute]

Only the very low current polyswitches have a DCR of 1ohm or more. See attached.

Also if you are running 4 ohm speakers you need a bigger current polyswitch dropping the DCR even more.

For an 8 ohm speaker protected to around 22 watts an RXE110 will do the trick and the DCR at 20c is between 0.15ohms and 0.25 ohms a far cry from 1 Ohm. (from Jaycars datasheet http://www.jaycar.com.au/images_uploaded/polyswit.pdf )

RXE110 pdf, RXE110 description, RXE110 datasheets, RXE110 view ::: ALLDATASHEET :::

the figure of .38 ohms 1 hour post trip is interesting and I would hope that it does return to the nominal resistance range after a while.

I've used polyswitches in the past and the did exactly what they were supposed too. Protected my drivers against over zealous party goers who pushed the amp into clipping. Before the polyswitches I had many a blown tweeter and occasionally a blown midrange!

Tony.