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Old 5th November 2005, 08:58 AM   #1
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Default simplest loudpspeaker dc protection

i was never into anything like this as speaker protection ckt.
but today,bec of a stray wire,my under test amp pumped tons of dc into my two way.result::tweeter survived(it had to bec of cap);but my $100 woofer gave out smoke and went dead

what is the simplest way to protect woofer.a 10nf cap in series?or a simple ckt?

i dont want repetition of todays events.help req.

thanks in advance
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Old 5th November 2005, 09:22 AM   #2
Did it Himself
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This is the Velleman K4701 kit and it does just what you want, just like you want it

Click the image to open in full size.
Schematic copyright Velleman
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Old 5th November 2005, 09:47 AM   #3
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Hello Richie00boy,
How does the shut off time compare to Transistor protection circuits built into the power stage of the average amplifier you can buy of the shelf so to speak?
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Old 5th November 2005, 09:48 AM   #4
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thanks a ton.

i had been searching the net for this but all i got was thrash.

it is too much simple.a bit of doubt does it affect sound quality in any way?

please tell me the specs of relay used.i have tda7294 amps in 70w continous mode.the 'suicide amp' was lm3876.plz suggest suitable relay ratings for tda amp.

also tell how can i vary its turn off time?
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Old 5th November 2005, 10:30 AM   #5
dnsey is offline dnsey  United Kingdom
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How about a fuse?
Quite common in pro speakers, and protects against AC overload too.
As it relies on the heating effect of the current, it will reliably protect the VC, as long as it's properly rated.
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Old 5th November 2005, 11:33 AM   #6
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The turn on delay is about the same as some typical transistor based circuits. You can make a transistor based one faster, but this one is perfectly fast enough.

The effect on sound quality would be a little more than a transistor based circuit, but I'd say you would be hard pushed to notice. The non-linear elements of the circuit are effectively out of circuit at normal audio frequencies.

The relay spec is given at the bottom. I use a commonly available 16A contact rated relay.

You can't vary the turn off time without changing the caps (which would have a knock on effect throughout the circuit), it simply remains on as long as there is DC present and shuts off when it's not, plus a few milliseconds whilst the caps discharge.
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Old 5th November 2005, 03:42 PM   #7
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thanks
if the effect on sound is audible only through 'audiophile ears',then this ckt is a very very nice one.i saw this on net at vellman site and saw its specs.i suppose by using higher current rated relay ,this circuit can b a full proof protection against malacious dc on the prowl to eat away the speakers
so simple,so cheap.i will make one and test it for slightest dc levels.

any other method in sight that is simple(i saw one using microcontroller!!)
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