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Multi-Way Conventional loudspeakers with crossovers

Thermistor removal from crossover rebuild?
Thermistor removal from crossover rebuild?
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Old 16th May 2020, 01:34 PM   #21
CliffR52 is offline CliffR52  Australia
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Quote:
Originally Posted by Galu View Post
If I may be so bold as to speak for Jon, then by 'more pleasing to the ear' I think he means 'compressed'. Compression is not desirable, but during an overload it is preferable to a distorted then ruined tweeter.

By 'Removal will make the tweeter respond as though it is not working', I think he is stressing that if you simply remove the polyswitch, you will break the circuit path and the tweeter will stop working. That is why I tell you to replace the polyswitch with a short length of wire.
Thanks for clarifying that.

Certainly wouldn't like compressed sound.

And, as I won't be abusing my speakers the lack of overload protection shouldn't be a problem.

I'll take the polyswitches out and run a wire in their place. Solves any issues, especially if they've already defaulted to a compressed state.

My Gale GS401's incorporate fuses.
Maybe this is a more favorable way of protecting Loudspeakers?
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Old 16th May 2020, 02:25 PM   #22
Galu is offline Galu  Scotland
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Quote:
Originally Posted by CliffR52 View Post
My Gale GS401's incorporate fuses.
Maybe this is a more favorable way of protecting Loudspeakers?
The trouble with fuses is that they do not automatically reset and have to be replaced when blown, which usually means dismantling the speaker.

There are different types of speaker protection and you may read about them here: TA Speaker Topics: Vent FAQ's

I suggest the summary given in the above link states all you really need to know:

Quote:
"The best method of protecting your speakers is to know their limits and stay within them. Blown speakers tend to be more of a live sound problem than a hi-fi problem. In live performance situations speakers are routinely operated at the threshold of death for extended periods of time."
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Old 16th May 2020, 02:46 PM   #23
JMFahey is offline JMFahey  Argentina
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Quote:
Quote:
"Recently I had an MS speaker to see for fix, had an issue of volume drop as it was fed more power. It was the polyswitches."
Quote:
"When they age, especially after when they had been triggered before, they tend to duck power early."
Well, they are doing their intended job!!!!
Quote:
volume drop as it was fed more power
Blowing the Tweeter will produce a more permanent and expensive type of volume drop, do you prefer that?

And there´s no "aging", simply today power is CHEAP and people tend to listen at stupid high levels compared to what original designers expected.
In any case, Tweeter voice coil will stand exact same power as before, protector will trigger at exact same power level as before, just use those fine speakers sensibly.
Quote:
if the polyswitch is considered dubious why not consider a lamp limiter to protect the tweeter?
^^^^^that.
Both are same thing, a PTC; lamp has way shorter thermal time constant though,on the other side does not "age", either works like the first day or burns.

An extra useful feature is that they provide a visual clue.

I make loud Bass amplifiers and speakers, (think Stadium use by Heavy Metal bands) and now and then somebody rings me: "Hey Juan, when slapping I see some kind of "lightning" inside the cabinets, the speaker cloth edges become inside lighted rings on the dark stage, is something wrong?"
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Last edited by JMFahey; 16th May 2020 at 02:56 PM.
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Old 16th May 2020, 02:56 PM   #24
MarcelvdG is offline MarcelvdG  Netherlands
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Quote:
Originally Posted by JMFahey View Post
Well, they are doing their intended job!!!!
Not quite, as ideally the trip level should stay at its initial value.

Quote:
Originally Posted by JMFahey View Post
Both are same thing, a PTC; lamp has way shorter thermal time constant though,on the other side does not "age", either works like the first day or burns.

An extra useful feature is that they provide a visual clue.
A disadvantage is that a lamp will cause more distortion, as due to the smaller thermal time constant, its resistance will vary more over a period of the signal. I haven't a clue if that is significant compared to the normal distortion of the loudspeaker, though.

Last edited by MarcelvdG; 16th May 2020 at 03:01 PM.
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Old 16th May 2020, 04:05 PM   #25
Galu is offline Galu  Scotland
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Quote:
Originally Posted by JMFahey View Post
And there´s no "aging"
A polyswitch (the subject of this thread) does suffer from 'aging'. A polyswitch which is made to operate constantly under overload conditions may no longer return to its low resistance state when cool and instead stabilise at a significantly higher resistance.
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Old 16th May 2020, 04:13 PM   #26
CliffR52 is offline CliffR52  Australia
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Quote:
Originally Posted by Galu View Post
A polyswitch (the subject of this thread) does suffer from 'aging'. A polyswitch which is made to operate constantly under overload conditions may no longer return to its low resistance state when cool and instead stabilise at a significantly higher resistance.
Is it worth replacing the polyswitch with a new one?

As I won't run ridiculous levels the replacement won't have to switch very often and maybe see me out.

It seems the polyswitch's achilles is age, and high frequency of tripping.
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Old 16th May 2020, 04:26 PM   #27
Galu is offline Galu  Scotland
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Quote:
Originally Posted by CliffR52 View Post
Is it worth replacing the polyswitch with a new one?
Only if you can source one with identical specifications. That may be problematical! Leave it alone or bypass it - nuff said!
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Old 17th May 2020, 12:01 PM   #28
Galu is offline Galu  Scotland
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Originally Posted by audiotechnica View Post
The correct ones are easy to get - Jaycar
I wonder which of the six PTCs shown in your link has the same specs as the PTC C995 in Cliff's Jamos, Ric?

The correct replacement is shown here: C 995, PTC thermistors for overcurrent protection - elpro Elektronik

The exact specs of the PTC C995 are given in this TDK publication: https://www.tdk-electronics.tdk.com/..._C935_C995.pdf
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Old 17th May 2020, 03:12 PM   #29
Galu is offline Galu  Scotland
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Originally Posted by audiotechnica View Post
?, can you post schematic please.
I share your ?, Ric.

13 ohm is a high resistance in this context and I would also like to see exactly where the PTC is positioned in the crossover.

Meanwhile, I agree that replacement with an identical PTC or, alternatively, 13 ohms worth of resistance are the options open to Cliff.
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Old 18th May 2020, 11:43 AM   #30
Kay Pirinha is offline Kay Pirinha  Germany
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I'd add: Replacing it with a 24 V 5 W automotive lamp will also do, as an incandescent lamp's cold resistance usually is about one tenth of it's nominal one. A lamp's decreased time constant (in comparison with a polyswitch/PTC) doesn't matter if it protects the squawker or the tweeter.
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