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Old 22nd May 2017, 05:59 PM   #1
xrk971 is offline xrk971  United States
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Default Speaker Protection Kit for under $5

I just ordered this kit as it was dirt cheap. I assembled it and tested it and it works surprisingly well. I don't know what the circuit is as no schematic (uses 6 identical transistors) is provided but the 3 second delay works and the DC protect cuts out at about 1v to 1.5v DC if sensed on inputs. Takes about 5 seconds to re-engage once DC is removed. If one wanted to, just change out the relays for quality name brand ones. For under $5, these are very nice and work as advertised. There is no reason why one shouldn't have a speaker protect circuit given how cheap and easy it is.

Has anyone else tried these?

Audio Speaker Protection Board DIY Components Kit for Stereo

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Here is my unit.

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If anyone knows the schematic of how this works that would be great to share.
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Old 22nd May 2017, 06:17 PM   #2
prasi is online now prasi  India
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they are on ebay and ali for long long time. I have 5 of them myself based on experience of Still4given.
Yes just change the relay to Omron G5LE, you are good to go. Transistor is S8050 general purpose NPN. works good.
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Old 22nd May 2017, 06:29 PM   #3
olafk is offline olafk  Germany
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I have already installed it three or four times. Works good.

regards Olaf
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Old 22nd May 2017, 07:13 PM   #4
xrk971 is offline xrk971  United States
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Good to know this unit has a good following already. Will the OMRONs have better relay contact quality or is it reliability we are buying?

Thanks for the feedback. Anyone have a schematic?
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Old 22nd May 2017, 07:25 PM   #5
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Hi, a bit more expensive than what you have there but comes with omron relays, I've built a couple, no problems AC 12-24V Circuit Speaker Protection Board DIY Amplifier Components Relay Kits
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Old 23rd May 2017, 03:27 PM   #6
AndrewT is offline AndrewT  Scotland
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I bought and have used many of these ultra cheap protectors/delays.

But as with all relay contacts they may not isolate in the presence of high DC currents.
I did make a few changes to use 24V supplies.
The sch can be got by reverse engineering the PCB.
It is very simple and easy to do.

And don't fit the third 15k.
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Old 23rd May 2017, 03:35 PM   #7
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^ Good point, I modified mine so speaker was on common terminal and toggled between amp and earth, many are not wired this way, it provides better protection for the speaker if there is arcing
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Old 26th May 2017, 11:34 PM   #8
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by AndrewT View Post
I bought and have used many of these ultra cheap protectors/delays.

But as with all relay contacts they may not isolate in the presence of high DC currents.
I did make a few changes to use 24V supplies.
The sch can be got by reverse engineering the PCB.
It is very simple and easy to do.

And don't fit the third 15k.
Why not use the third 15k?

This board is actually quite compact and could even be used for a desktop headphone amp. Most headphones can take 1.5vdc (the trigger point) so probably better than no protection.
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Old 27th May 2017, 07:56 AM   #9
AndrewT is offline AndrewT  Scotland
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the third 15k is across the "timing" capacitor.
That can ruin the timing to such an extent that the relay does not trigger.
In my view using a simple RC from an unregulated supply is a bad timer. Adding in the third resistor turns a bad timer into a worse one.

If you were to run the isolator from a regulated supply which then turns it into a resonable timer, then you find that the effect on timing of adding that third 15k is not as bad and can leave you with an effective way of "tuning" the delay period.

But I just miss it out and tune the delay by using a suitable value of plastic film capacitor where there is space to accomodate such.
Using an electrolytic REQUIRES one to slowly reform it to well above any voltage it may see in future operation. One of the biggest risks of using an unreformed electrolytic as the timer element in an unregulated arrangement is non triggering because the 15k and the electro draw so much "leakage current" that the timer NEVER triggers.

Finally before you try any of these unknown (no build guide) contraptions, it is incumbent on the user to first understand how it works. Then critically assess it's ability to do the job you the user requires.
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Last edited by AndrewT; 27th May 2017 at 08:01 AM.
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Old 27th May 2017, 02:23 PM   #10
borys is offline borys  Ireland
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xrk
I do not know mentionet DC protector schematic but You can use my one from headamp, very simple few component one. To add extra feature as a supply use single diode half way rectifier and NPN tranistor with biased zener diode in the base and You will have fast OFF feature when transformer is OFF.

Regards
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