Adding a "Protection LED" on an amp

Bricolo · 30th May 2003, 02:56 PM

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

davesaudio · 30th May 2003, 03:11 PM

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?

thylantyr · 31st May 2003, 12:00 AM

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?

Cobra2 · 31st May 2003, 12:39 AM

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

Arne K

Bricolo · 31st May 2003, 10:09 AM

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

davesaudio · 31st May 2003, 01:07 PM

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?

Bricolo · 31st May 2003, 02:18 PM

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

thylantyr · 31st May 2003, 08:24 PM

666 ?

That is the devil.

Get some holy water, sprinkle
on amplifier.

/joke

Bricolo · 31st May 2003, 10:20 PM

I don't think my amp will like water, holy or not

JojoD818 · 2nd June 2003, 04:23 PM

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

30th May 2003, 02:56 PM	#1
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	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

30th May 2003, 03:11 PM	#2
davesaudio diyAudio Member Join Date: Feb 2003 Location: GTA	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? __________________ intentionally blank

31st May 2003, 12:39 AM	#4
Cobra2 DIY ! diyAudio Member Join Date: Apr 2002 Location: Stavanger, Norway	Clipping indicator Here...(for the Leach Amp): http://users.ece.gatech.edu/~mleach/...phics/clip.pdf Arne K __________________ Ars longa, vita brevis

31st May 2003, 01:07 PM	#6
davesaudio diyAudio Member Join Date: Feb 2003 Location: GTA	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? __________________ intentionally blank

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31st May 2003, 12:00 AM	#3
thylantyr diyAudio Member Join Date: Feb 2001 Location: Mars	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?

31st May 2003, 10:09 AM	#5
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	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

31st May 2003, 02:18 PM	#7
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	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

31st May 2003, 08:24 PM	#8
thylantyr diyAudio Member Join Date: Feb 2001 Location: Mars	666 ? That is the devil. Get some holy water, sprinkle on amplifier. /joke

31st May 2003, 10:20 PM	#9
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	I don't think my amp will like water, holy or not

2nd June 2003, 04:23 PM	#10
JojoD818 diyAudio Moderator Join Date: Mar 2003 Location: diyAudio Special Operations Center	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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