Speaker power protector/limiter by David Tilbrook - Page 2 - diyAudio
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Old 6th September 2012, 07:57 AM   #11
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Quote:
Originally Posted by Ian Finch View Post
I don't follow that you have 4 speakers to switch so you want four sets of contacts but you also want to put them in parallel?? That seems to defeat its purpose.
In the case of using a relay with four sets of contacts, each contact will switch a single speaker of course. Placing the relay contacts in parallel I thought only do in case of using another HEF4050 and two DPDT relays for switching only two speakers.

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Ideally you need to sense each channel separately and sum the inputs at the 4050
Is there a simple way to do this keeping in mind that the schematic remains self-powered?

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to do that with 1 relay or better, have individual relay circuits on each channel output (if you do actually have separate channels here)
What I have is a 2-channel amplifier and four speakers...therefore, each channel has two speakers in parallel.

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I had forgotten to say that 5W/8R power would not generate enough voltage after the rectifier, to drive the circuit. I suspect that a nominal 15W amplifier wouldn't either. Schottky diodes would help, but how much will depend on relatively high signal levels.
Is there a simple way to use voltage multipliers (as in the attachment below), instead of a single diode bridge, to double, triples, etc. input AC voltage from amplifier?
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File Type: gif Voltage multiplyers by ilimzn.gif (15.0 KB, 98 views)
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Old 6th September 2012, 09:55 AM   #12
AndrewT is offline AndrewT  Scotland
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Is this a power detector?
Or is it a DC offset detector?

The relay on the output will isolate the speaker when the input is "triggered".

But the reaction time will be too slow for an effective power protection scheme.
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Old 6th September 2012, 10:14 AM   #13
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Hi Andrew,

It's just a thing that will isolate speakers from an amp when a certan power is reached, so it's is a power detector I guess. I'm not looking for a DC offset detector nor I'm interested in reaction time...the thing just have to limit loudness (like 65dB or so), that is all.
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Old 6th September 2012, 12:06 PM   #14
AndrewT is offline AndrewT  Scotland
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A slow acting speaker isolation relay cannot limit SPL and certainly not effectively.
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Old 6th September 2012, 12:19 PM   #15
muzza is offline muzza  Australia
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This is one I use.
It does:-
DC protection
Mute on powerup ("de-thump")
Immediate disconnect on power-off
Softstart.
Mains power servo (so a small mains switch can be used).
It is controlled with a small PIC 12F675 microcontroller.
(note this was the first PCB and I had not fitted the mains fuse as yet...must take a picture of a completed version)
Have used a bunch of these in DIY amps as well as fitting to commercial units).

The loudspeaker part is expandable.
The speaker relays are mounted near the outputs of the amp and the driver for these would run at least six 12v relays.
The board has two DC sense circuits on board and can be expanded to any number of channels.

Also have a look at the DIYaudio version in the DIYaudio store as well.
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Old 6th September 2012, 12:27 PM   #16
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Quote:
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A slow acting speaker isolation relay cannot limit SPL and certainly not effectively.
Are you saying that schematic (and finish product) in my first post can't limit SPL effectively...why?
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Old 6th September 2012, 12:41 PM   #17
AndrewT is offline AndrewT  Scotland
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The relay and it's activation is too slow.
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Old 6th September 2012, 12:51 PM   #18
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OK, I now there will be some delay until elcap charge, Tr activate etc., so what is your best gues for total delay until relay fires?
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Old 6th September 2012, 01:01 PM   #19
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about 200 cycles of 10kHz transients.
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Old 6th September 2012, 01:08 PM   #20
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20ms is good enough for me and the purpose. I would not mind if the whole system continues to play the next 980ms. Remember, I'm not trying to protect anything (amplifier and/or speakers), just want to be able to limit SPL.
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