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Topic: When good opamps go bad... |
Steven Paris
From:
Los Angeles
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Bill Terry
From:
Bastrop, TX
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Posted 19 Oct 2018 6:38 am |
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| I haven't looked at that page in a long time, but it's always had interesting stuff. Cool article.. |
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Keith Hilton
From:
248 Laurel Road Ozark, Missouri 65721
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Posted 19 Oct 2018 7:07 am
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| Reminds me of why I put a lot of extra protection in my circuits. Good article. I have sometimes wondered if the extra parts, extra labor, and extra space on the circuit board for extreme protection is worth it. Then when you read an article like this, it is comforting to know you did everything you could do to prevent failure. |
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Keith Hilton
From:
248 Laurel Road Ozark, Missouri 65721
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Posted 19 Oct 2018 9:03 am
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Most designers do reverse polarity power protection. Not all designers do current limiting resistors. Very few designers use resettable fuses. I think I am the only one who uses fuses on both power rails. Almost "NO' designers tie off the inputs and outputs with diodes. Those that do tie off the inputs and outputs normally use 1N4148 signal diodes. Many years ago I saw Peavey electronics using this 1N4148 protection. I researched why Peavey was adding this protection from a book called the OP AMP Cook Book, by Author Walter Jung. In most cases the 1N4148 diodes provide enough protection, but I have had them blown out on the output. There has been 3 or 4 times in the last 21 years where I have had to up the strength of the diodes, "only" on the output. Old "tube" amps with the ground lug cut off, or capacitors worn out, can send a lot of voltage out to anything connected. Also guys hooking two amps in the signal chain, or several devices in the signal chain, can cause great differences in ground potentials.
Like I said, almost no designers tie off the input and outputs of Op Amps with diodes. The only ones I have seen doing this is Peavey Electronics and Hilton Electronics. There may be other designers--I have just not seen any, other than the two mentioned! Designers get away with not adding this diode protection on the input and output because most of the damage is slow to happen, or happens in time by an event. By then the device is "OUT OF WARRANTY"--and because of the age of the device, the designer is not blamed for anything. I have wanted to quit adding the 4 protecting dodes many times over the years---but reading this article makes me happy I have kept the protection.
Consumers need to be aware that people who build and sell electronics do it to make money. More money is made if you cut corners. It takes time, labor and money to add protection to a circuit. All the consumer sees is the slick advertising and his buddy who has one. Most of the electronics coming from China has little if any failure protection---the China price is cheap and that is all that matters to some people. Then there are products with advanced features, that have a high price tag. Beware--a high price tag "does not guarantee" the guy who designed the circuit cared about protection modes. Sometimes a very high price tag is a tool used by sellers to make you think you are getting something special. What really matters for the long term is the protection that is build into the circuit board---by a designer who cares about failure modes. Buyer beware! |
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Georg Sørtun
From:
Mandal, Agder, Norway
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Posted 20 Oct 2018 2:08 am
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| Keith Hilton wrote: |
[…]
Consumers need to be aware that people who build and sell electronics do it to make money. More money is made if you cut corners. It takes time, labor and money to add protection to a circuit. All the consumer sees is the slick advertising and his buddy who has one.
[…]
Beware--a high price tag "does not guarantee" the guy who designed the circuit cared about protection modes. Sometimes a very high price tag is a tool used by sellers to make you think you are getting something special. What really matters for the long term is the protection that is build into the circuit board---by a designer who cares about failure modes. Buyer beware! |
Cannot be written much clearer. |
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Paul Arntson
From:
Washington, USA
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Posted 29 Oct 2018 5:48 pm
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Good article. Thanks, Steve!
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Excel D10 8&4, Supro 8, Regal resonator, Peavey Powerslide, homemade lap 12(a work in progress) |
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Rich Upright
From:
Florida, USA
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Posted 11 Nov 2018 4:27 pm
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I did not understand 1 word of the article.
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A couple D-10s,some vintage guitars & amps, & lotsa junk in the gig bag. |
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Paul Arntson
From:
Washington, USA
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Posted 12 Jan 2019 11:09 pm
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Differential input voltage range on the LM358 is +/- 32 volts.
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Excel D10 8&4, Supro 8, Regal resonator, Peavey Powerslide, homemade lap 12(a work in progress) |
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