Make use an element that will increase its resistance when there is excessive current. Depletion JFET with low Rdson.
There are reasons why we choose the best resistance around opamps. You need to know your opamp. Changing the resistance will change its performance.
The main reason to choose higher resistance with old opamp is because its performance will drop significantly with low load resistance.
Back in the day at Advanced Audio Lab in New Orleans I replaced hundreds possibly thousands of input diff pairs. We really did not fully understand the cause and neither did any of the factory engineers. That would be McIntos,Marant,Pionee,Sansu,PhaseLin,Fishe,SAe and many others.
Generally the symptoms were a popcorn sound, intermittent hi offset, all at totally random times. The engineers looked at using different pairs , input slew rates etc.
To this day I imagine it still remains somewhat of a mystery.
And yes some even raised the possibility that they were 'wearing out'.
Generally the symptoms were a popcorn sound, intermittent hi offset, all at totally random times. The engineers looked at using different pairs , input slew rates etc.
To this day I imagine it still remains somewhat of a mystery.
And yes some even raised the possibility that they were 'wearing out'.
May be nigel wanted to make sure the opamp is always powered when the signal kicks in.
It seems a good idea to keep an op amp powered. Very often we find good ideas are not. For example asperin 75 mg a day. The fashion has changed.
If it is not too far off topic would people like to try something. NASA and the Moon. I saw a film of the feather and the metal ball experiment on the Moon. At last something to look at we might test. 1.2 metre drop in what seemed like 1.2 seconds. I felt it safe to say if fake they at least thought it through. The feather looked a bit odd as if it was heavy, doubtless it would. My friend Julian said he noticed if the Moon walks were fake at least the dust settled as if in a vacuum. One way we might tell is see if the video frames are exact duplicates when the feather falls, there should be almost a DNA of imformation. Doing 2.5 shots might show that.
1.62 M/s Moon and about 9.8 M/s Earth. 1:6 for this arguement. I plan to use a metal ball and aluminium foil sheet with my data logger to do a real life test. The ball would have a thin wire on it. Good enough I feel
Here is the weirdest thing. Subjectively, dropping a moderately heavy object 1.2 meters seemed to take the same time as the NASA Moon video in my front room. What part of S=ut + 1/2at^2 did I get wrong? I only used a counting test. All the same it seems it should fall quicker. Subjectivity is bad news or even fake news! If very wrong I still wouldn't have counted to 1. BTW, this isn't about am I right. It just is saying things are not always as easy to test as they should be on the spot tests. If only for fun try it. I really doubt you will get 0.5 second.
If it is not too far off topic would people like to try something. NASA and the Moon. I saw a film of the feather and the metal ball experiment on the Moon. At last something to look at we might test. 1.2 metre drop in what seemed like 1.2 seconds. I felt it safe to say if fake they at least thought it through. The feather looked a bit odd as if it was heavy, doubtless it would. My friend Julian said he noticed if the Moon walks were fake at least the dust settled as if in a vacuum. One way we might tell is see if the video frames are exact duplicates when the feather falls, there should be almost a DNA of imformation. Doing 2.5 shots might show that.
1.62 M/s Moon and about 9.8 M/s Earth. 1:6 for this arguement. I plan to use a metal ball and aluminium foil sheet with my data logger to do a real life test. The ball would have a thin wire on it. Good enough I feel
Here is the weirdest thing. Subjectively, dropping a moderately heavy object 1.2 meters seemed to take the same time as the NASA Moon video in my front room. What part of S=ut + 1/2at^2 did I get wrong? I only used a counting test. All the same it seems it should fall quicker. Subjectivity is bad news or even fake news! If very wrong I still wouldn't have counted to 1. BTW, this isn't about am I right. It just is saying things are not always as easy to test as they should be on the spot tests. If only for fun try it. I really doubt you will get 0.5 second.
I think I jumped to my version or Galileo example. As I understand it Aristotle had said it was obvious heavy beats light. No one dared say not true. I have seen on TV a painting of Galileo, some musicians, a slope, two balls and a trap door. The ball going down the slope allows the second ball to fall vertical as it passes. The two balls hit the floor at the same time. However the first ball from new time zero when the second ball falls goes further ( it would ) That's S= ut + 1/2at^2. The ut being added as simple addition. Not unlike an op amp maths I guess. The musicians overcame the problem I am having. They were the better timing devices. Mr G wanted to know if it ( g ) was constant.
I am reasonably convinced this is the Moon in the link. In both Earth and Moon it almost looks as both are slower than they should be. Perception rather than reality. We now find like beliefs, believing we went to the Moon is a matter of faith. As to the flag that fluttered on the Moon when it shouldn't UK's James Burke said it would some time before on live TV. He said NASA thought it would be boring if the flag was limp or flat. Look at the trouble that caused. That flag was reasonably see through which explains other things said. Complex reflections also say why lighting is unusual, the Moon is not 100% flat. I do think some photo's were not on the Moon. Maybe the space guy were rotten photographers like me.
The Apollo 15 Hammer and Feather Drop on the moon (1971) - The Kid Should See This
Anyway decided to make the opamps replaceable and add four 1k limiting resistors . One pair for each side of the opamp. Board is larger now.
I still think this is a component the chip mfgr should have built in and laser trimmed.
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Would destroy the purpose of low noise op-amps.
Protecting Off-Amps | Analog Devices
You could also just disconnect the input when the power is off.
There are some parts that have internal protection, but they aren't the greatest for audio, like ADA4177.
Op Amp Input Overvoltage Protection | Analog Devices
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If you TRULY BELIEVE that laser trimming the current limiter 1K series resistors is important, you can achieve the same result on your board full of discrete, not integrated, components. Simply purchase a large number of 0.1% 1K resistors from the low cost line item at Mouser, and then methodically winnow them down to one or two matched pairs, using a 7 digit benchtop meter made by Fluke or Kiethley or HP, that you purchase used for $300. I bought my benchtop 7 digit meter from John Bau who is a member of diyAudio, and who does business as linearz dot com, in case that helps. Presto, 100ppm matching for ten dollars of additional "marginal cost", and/or 10 ppm matching for a hundred dollars of additional "marginal cost". You pays what you wants and you gets what you pays fo.
What the user does with the (composite)part is something I can't predict and I also have no control over the target assy.
Ie power on/off , large amplitude square waves or a single fast rise time event etc.
It is my job to provide reasonable protection for the part.
Input current limiting falls within the scope of what is reasonable.
The chip mfgr should have addressed it (as diodes are on the die).
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Ie power on/off , large amplitude square waves or a single fast rise time event etc.
It is my job to provide reasonable protection for the part.
Input current limiting falls within the scope of what is reasonable.
The chip mfgr should have addressed it (as diodes are on the die).
.
My life would be hell without op amps. If only a few at OK prices had +/- 50VDC rails even if it meant low current life would be better. The Pentawatt T0220 package would suit. A beefy NE5534 would do with same comp and noise ideally. I usually build something op amp like to do that. Much as I pretend to dislike 5534/32 they often start the ball on it's way. If you need something in a hurry the 1971 PW Texan amp is workable.
Since I am not an EE, I can only comment on subjective aspect of opamps. I must say that it is very difficult, in fact almost impossible, to surpass opamps sound quality in line level applications, even with very complex discrete circuits. Even adding discrete current boosters at the output of opamp does very little for sound quality. All you need is opamp. And all this applies to industry standard opamps, not to speak about high performance opamps. You would need extremely good hearing, perfect room acoustics and really expensive gear to notice improvement with discrete circuits.
And if a small compromise can be allowed we can swap them like vacuum tubes. I just have done this and have some new mesurements that slightly go against commonly held opinions. My bigger problem was reading the types to be sure they were in the corrct draw. It took sun light and a magnifying glass to do it. Glad I did as one was wrong. Who is it who thought white paint for op amps bad and used same colour paint instead?
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