polyphase switch?

[aborza]

Hi,

I read here about a "polyphase switch" to protect speakers.

What is it?

How does it work?

Do they come in sizes?

Where do you get them?

Can they protect all drives in a multi-amped system. By that I mean do they protect subs, woofs, mids and tweeters? Of course I understand that there will be one poly phase switch for each driver. No?

Any tricks about their use?

Do they affect sonics?

Thanks

ab

[daatkins]

I think you mean the Polyswitch manufactured by Raychem. They are kind of like PTC thermistors but have a more abrupt transition from "low" ohms to "high" ohms. They're available from a lot of places; Parts Express carries them.

There's a PDF about use protecting speakers here:
http://www.circuitprotection.com/02D...a/03.C12_loud_(118-121).pdf

As for affecting sonics, I'm sure they will do to some degree or another but I've never used them so can't comment.

Nice one,
David.

[mrfeedback]

Sonics is affected slightly in normal operation.
When operating on the edge of triggering, positecs cause a compression characteristic, and whilst not unpleasant is quite obvious.

For the price they are a good investment for protecting tweeters, especially if other people may be operating the speakers.
Mission speakers used these.

Eric.

[djdan]

Polyswitch is very useful if you know how to use. If it is used only to protect speakers for overload is very cheap and reliable.

Example :

If you want to protect a speaker rated for 40W RMS /8ohms , use RXE160.

For tweteers use RXE110 or RXE090 but only in the crossover input.


I know people how insert polyswitch on amplifier outpout and in many situations it is a good solution.

[Nelson Pass]

My experience with these is that you don't really want to
be passing high quality audio through them.

Low quality, OK....

[djdan]

This summer I had an interesting experience.

Somebody buy a pair Cabasse loudspeaker TC21 ( 1300 USD/pair ) and a pair 30M20 . He make a cheap protection for TC21 mid/high with polyswitch (RXE165) inserted in amplifier and he put a secret switch to by-pass the polyswitch when he listen.

If it play not too loud ( well , 20W averige to 100w peak ) it is not any diference if the switch is off or on.

Nelson , if you will make this test I think you will have a big surprise.

My conclusions about polyswitch is :

1. If somebody want to listen music very loud it it better to use polyswitch.
2. If the speakers it isn't overloaded the polyswitch is simple wire with no sound degradation.

[Nelson Pass]

If it sounds good enough to you, then OK, but I have to
say the Polyswitch has a nonlinearity to it, and you can
measure it.

[peranders]

Originally posted by Nelson Pass
If it sounds good enough to you, then OK, but I have to
say the Polyswitch has a nonlinearity to it, and you can
measure it.

The polyswitch has rather high "ON" resistance. Best fuse is a ordinary melt fuse , slow if you want to have some "music power". The rating should be a little bit lower the the rated current. But seriously, you can most of the time feel how loud you can play with a certain speaker. When it starts to sound bad it's usually too loud.

[alaskanaudio]

I use the polyswitch in power supplies where protection is required but use of regular fuses is not desired due to the impracticality of using them in some locations. Polyswitches were designed just for such applications, and they work extremely well for this purpose. My 1R1 MOSFET power amplifier uses a number of these to protect the power transformer lower current secondary windings from any potential over current condition that may damage these windings.

Polyswitches will hold a near constant low resistance up to there rated current, then as they heat up the resistance rises extremely rapidly to almost a open circuit by limiting the current just enough to keep the polyswitch nice and warm. The heat produced by the polyswitch controls the resistance. After the initial over current condition is removed they cool down and act like low value resistors again.

I don’t believe that Polyswitches were ever meant to pass high quality audio signals. Any such use should be avoided. Their primary use is to limit currents in power supplies and the convenience of automatically resetting themselves when they cool down. With the use of the proper value polyswitch there is never a fuse to replace.

Don't go through all the trouble of building a nice amplifier and then have its output signal changed by a temperature dependant resistor such as a polyswitch. The best way to protect tweeters is to assure that they are never over driven.

Johannes Fassotte
Alaskan Audio

[peranders]

Also one more thing to keep in mind: These fuses can break a LIMITED number of times. They don't last forever if the have "fused".