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Old 30th May 2003, 02:56 PM   #1
Bricolo is online now Bricolo  France
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Default Adding a "Protection LED" on an amp

I've seen many commercial amps that have a "protection" LED, that lights when the amp goes in a kind of protection mode, in example when it's oscillating


Has anyone a schematic for this?

PS: there's no need for short circuit protection; since it's for a gainclone. My principal aim is to see easilly if the amp oscillates

Thanks
Alex
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Old 30th May 2003, 03:11 PM   #2
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This is a topic of interest for me as well.

This is more of a question than an answer : When they oscillate are they driven close to the rail voltage?
would a clipping indicator work?- comparator with threshold
close to rail voltage?
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Old 31st May 2003, 12:00 AM   #3
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I saw a schematic in the Slone
audio book for an usual DC offset
detector with oscillating output
detection. It had output series resistor andinductor.
The voltage sense taps off the inductor..
I don't know too much about it, I wasn't interested in the design......

I guess the voltage rises at oscillation
triggering the DC offset detector.

Or make a high frequency detector


high pass filter at > 50khz
that triggers when voltage > threshold?

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Old 31st May 2003, 12:39 AM   #4
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Default Clipping indicator

Here...(for the Leach Amp):
http://users.ece.gatech.edu/~mleach/...phics/clip.pdf

Arne K
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Old 31st May 2003, 10:09 AM   #5
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thanks

but this is to indicate clipping, isn't it?

does this work for oscillation? oscillation isn't always a high voltage, I saw amps oscillates at 2Vpp
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Old 31st May 2003, 01:07 PM   #6
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are these oscillations always a high frequency?
highpass+ threshold?
I have been thinking a zero crossing detector would capture all DC problems but the oscillating case is not detected. maybe setecting something in the feedback path?
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Old 31st May 2003, 02:18 PM   #7
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when my gainclone was oscillating, it was at 666kHz, 2V

with a zobel (10R+0.1uF) and 200uF added PSU caps, it's reduced to 10-20mV, still 666lHz
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Old 31st May 2003, 08:24 PM   #8
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666 ?

That is the devil.

Get some holy water, sprinkle
on amplifier.

/joke

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Old 31st May 2003, 10:20 PM   #9
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I don't think my amp will like water, holy or not
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Old 2nd June 2003, 04:23 PM   #10
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How do I use the clipping indicator for the leach amp? Do I just connect the output of my amp to the one labeled "output"?

Can I use this for my other amps?

Jojo
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