SDA Polyswitches Are Nasty

MillerLiteScott

I ran my 2B TL's with jumpers in place of the poly switches and thought they were a little bright. I replaced the jumper with a .5 ohm 12 watt Mills at the same time I sealed the cabinets better and through bolted my bolts for the spikes. What I found was that the sealing and through bolting increased my bass enough that my 2B TL's were a little to veiled with the .5 ohm 12 watt Mills so I removed the Mills and replace them with a jumper and my sound seems to be balanced top to bottom IN MY ROOM. I have also placed my 2B TL's on 3 1/2" thick laminated maple speaker stands that are also spiked to the concrete slab through carpet which may have contributed to a different sound.

Scott

NJPOLKER

George call me when you get a chance.

DarqueKnight

heiney9 wrote: »

Blashphemy!!!!! A Polk speaker not properly protected..............


Oh My Lord.................what will happen to the poor 3.1TL? :eek:

H9

I think most of them have blown up by now.:(

That must be why there are so few sightings of them...for sale or in people's rigs.:rolleyes:

flason

Anyone have a step by step guide to replacing the switches? Or is it a pull the old and solder new? Pics would be very helpful.

george daniel

this might help

http://www.polkaudio.com/forums/showthread.php?t=47379&highlight=polyswitch+removal

WastelandWand'r

I pulled the polyswitch and replaced it with the recommended Resistor. Am I assuming correctly that the 750pf bypass cap is the brown two legged ant in the C4 positiion on the board? And if so, that it is removed and not replaced or jumped after its removal?
Correct?
Any help greatly appreciated as I am staring at it getting more and more confused.
Nathan

WastelandWand'r

F1-- Thanks for the reply.
Nathan

F1nut

Glad to help.

stubby

Removed the poly on my right channel SRS 2 and what a difference. I could tell the right side wasn't quite as loud as the left so I did the deed.

Sound is much more balanced now between the speakers. The center image was shifted slightly to the left before, now it is smack dab in the middle with much more clarity.

Until I get the rest of the caps and resistors for a crossover redo, I am happy with what I have. Think I'm going to go with the TL mod.

stubby

Conradicles

Pretty sure this Mundorf 0.47 ohm 10 watt resistor would work as well to replace the poly correct?
http://www.madisound.com/catalog/product_info.php?products_id=8420

audio_alan

I've been thinking about replacing my Polys recently, but also like the idea of the extra protection. Has anyone thought of making a mod that lets you have the best of both worlds?

Here's my idea: Modify the binding post plate to accomodate a jumper, resistor, or polyswitch which can be quickly/easily swapped out.

Why? Say I really want to crank one night, but don't want to damage my tweeters. No problem, I could go to the back of each speaker, pull out the resistors and stick in the polyswitches. .... CRANK away..... Then, when I want to go back to regular listening mode (where there is very little risk of damaging the tweeters), switch back to a plain jumper or resistor.

Does this seem worth the trouble? Would such a setup actually degrade the signal because it wasn't soldered into place?

Just trying to think outside the box a bit....:rolleyes:

ben62670

You could look into using a circuit breaker designed for speaker protection. They are better than poly switches, but not as good as nothing at all.
http://www.parts-express.com/wizards/searchResults.cfm?srchExt=CAT&srchCat=568&CFID=31819987&CFTOKEN=45257455

audio_alan

ben62670 wrote: »

You could look into using a circuit breaker designed for speaker protection. They are better than poly switches, but not as good as nothing at all.
http://www.parts-express.com/wizards/searchResults.cfm?srchExt=CAT&srchCat=568&CFID=31819987&CFTOKEN=45257455

Thanks for the link, Ben. Have you (or anyone else) tried one of these Speaker Circuit Breakers in place of a poly switch? Do they also degrade over time like the poly switches?

I notice that there are several different models. How would I determine what "power level rating" (as they put it) to choose the appropriate one? I would assume that would depend on the amp I'm using to feed them, correct?

ben62670

Look up the rating of the existing poly switch.

audio_alan

The SRS schematic says it's a RDE-090A. According to this site...

http://www.westfloridacomponents.com/F027/40A+30V+Resettable+Fuse+POLYSWITCH+RDE090A+RUE090.html

... the values of those poly switches are: 40 Amp , 30V , .9A Hold Current, 1.8 Amp Trip Current

Forgive me if my electronics knowledge is a bit rusty, but if I do the calculations to find the wattage for the poly switch:
W = V * I
W = 30 * 40
W = 1200 watts

None of the speaker circuit breakers are close to that. The .85A and 1.0A are close to the amperage, with a 200% trip bringing them to 1.7 or 2.0 (still close to the 1.8 trip of the original), but the watts are MUCH lower (60 and 70 watts respectively). Even if I double the wattage (as I think I would need to because the SRS's are 4 ohm speakers, and the speaker circuit breakers say they are based on 8 ohm loads), that's still not even close to 1200 watts. Am I'm missing something? Can I just ignore the wattage? Sorry, electronics class was a loooong time ago. :biggrin: Thanks for your help.

ben62670

The 40amp is max currant to device fail.
here is a close poly switch to compare.
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=071-262

audio_alan

Ok, so if I understand correctly, those polyswitch specs are actually just max tolerances. The 40 amps is the max amps it can pass before failure, so the 1200 watts figure that I calculated is bogus because that's based on the absolute maximum. Conversely, the speaker circuit breakers on the webpage you supplied shows them spec'd at more reasonable operating values.

If so, it sounds like the key specs that I need to match are the Hold Current and the Amp Trip Current. The would mean the .85A/40W (on the tight side) or the 1.0A/70W (on the high side) speaker circuit breakers would be the suitable/superior replacement parts over the stock polyswitch, correct?

ben62670

Correct. I would err on the lower side. If it trips often you can get the next size up.

audio_alan

Ok, thanks Ben. Regarding this statement you made: "better than poly switches, but not as good as nothing at all."

Are the speaker circuit breakers better because their tolerances don't adjust after tripping (like the polyswitches do), or do they just sound better?

ben62670

Breakers are actually a switch(like a relay). Poly switches are resistive thermal switches. They open when they get hot.

audio_alan

ben62670 wrote: »

Breakers are actually a switch(like a relay). Poly switches are resistive thermal switches. They open when they get hot.

So if the breakers are a switch, I assume they trip faster? Any difference in sound quality? Sorry to ask so many questions. Like I said, electronics class was a long time ago, and without using it much over the years, I've forgotten most of it...

BTW, are you still in the cross-over redoing business, Ben? If so, please PM me. Thanks.

ben62670

A poly switch has to heat up via a small resistance. I am not sure what trip the breaker, but it was explained to me that they are more like a relay.

OldmanSRS

Technically a PolySwitch resettable device is a conductive polymer based thermistor. Thermistors are characterized by either negative temperature coefficient behavior (NTC) where the resistance of the device decreases with temperature or positive temperature coefficient behavior (PTC) where the device resistance increases with temperature. A PolySwitch resettable device is a polymer positive temperature coefficient thermistor.
In comparison to bimetal circuit breakers, the main difference is latching behavior. Although both the bimetal and the PolySwitch are resettable devices, many bi-metal circuit breakers will reset themselves even when the fault is still present. This can lead to large electro magnetic interference (EMI) spikes on resetting The PolySwitch device, however, latches in the high-resistance state until the fault is cleared and power to the circuit is recycled.

audio_alan

From OldManSRS's explanation, it sounds like the polyswitches are a safer bet. Decisions, decisions. :rolleyes:

I still like the idea of just a jumper/resistor, but sometimes I don't trust myself with the volume knob :biggrin: (which is why I suggested the "best of both worlds" jumper/resistor/polyswitch quick interchangable mod). I still think that mod could work. I don't see how that mod would differ much from fuses that you put on the back of speakers. Sure, it would be another non-soldered connection, but so are the connections from the amp to the speaker wire, speaker wire to the binding posts, and the internal speaker wire from the board to the drivers.

FYI - I'm currently powering my SRS's with an Adcom 555 mk II, and the polyswitch on my left speaker engaged a couple times last week. I suppose it could be because they are old though, and just tripping too easy?

heiney9

The problem with putting a "mod" on the speaker terminals is then the "mod" is receiving a full signal. The poly switch when located in the proper part of the PCB is just monitoring the tweeter array. Fuses are wired into the tweeter circuit when on the terminal cup.

Either replace the poly with a modern one or delete it and watch the volume control. I've owned Polks all my life and I can't think of more than 2 times I've ever tripped a poly. Practice restraint.

H9

audio_alan

heiney9 wrote: »

The problem with putting a "mod" on the speaker terminals is then the "mod" is receiving a full signal. The poly switch when located in the proper part of the PCB is just monitoring the tweeter array. Fuses are wired into the tweeter circuit when on the terminal cup.

...

H9

I agree that you wouldn't want to put that mod in-line with the full signal. However, I was suggesting running wires from the circuit board (where the polyswitch is) to the binding post cap, not the binding posts themselves. Then there would be basically a "junction box" that allows you to complete the same polyswitch circuit as before, but with your choice of a straight jumper, a resistor, a polyswitch, or even a speaker circuit breaker. It would not change the location of where the polyswitch interacts with the circuit. The only difference would be an extra 16-24 inches of wire to travel, and it would be a non-soldered connection. Otherwise, I would assume it would behave the same. Make sense?

The only question would be whether the extra 16-24 inches of wire would pose a problem? I would think that short of a distance would be negligable in the grant scheme of things...

I'm not totally sold on the idea myself. Just kicking it around...

heiney9

It does make sense but the length of wire would dramatically increase the time before the poly breaks the circuit. That distance of wire will dissipate the heat generated when overdriving your tweets. Heat is what causes the ploy to open. Unless you can come up with a formula that compensates for that and then use the appropriate poly. Sounds like an awful lot of work and research to me.

Atleast with a fused system the wires are much shorter and I'm sure the value of fuse was choosen based on the length of the wire from the terminal cup to the x-over.

H9

audio_alan

heiney9 wrote: »

It does make sense but the length of wire would dramatically increase the time before the poly breaks the circuit. That distance of wire will dissipate the heat generated when overdriving your tweets. Heat is what causes the ploy to open. .....

H9

Great point! I hadn't thought of that. I suppose I could try very sensitive polys, all the way up to the stock values. Trial and error might get me close. Or, I might just fry all my tweeters before the wire ever got hot enough to trip the poly. :mad: Ok, scratch that idea. It never hurts to think outside the box though...

heiney9 wrote: »

....

Either replace the poly with a modern one or delete it and watch the volume control. I've owned Polks all my life and I can't think of more than 2 times I've ever tripped a poly. Practice restraint.

H9

BTW - Restraint, what's that? Being a guitarist who is used to standing in front of loud amps and drums, sometimes I just have to turn it up to "11".

F1nut

Buy a mo' better amp.

hearingimpared

^^^^ right on the money. I got a "mo' better" amp and use jumpers in lieu of polyswitchs (I've not tried the resistor tweak yet) and have no fear at all of turning my volume dial past 3 o'clock when I'm really rockin'.