Scott, the direct replacement for the LME4990 is the AD797. I designed the JC-3 with the AD797, but found that the LME4990 would sound as good, and was much cheaper in price. Now, I have not, until now, had a need to replace the LME4990, but what else does AD have that will sound as good as the AD797, but offered at a lower price? Please be serious now, and don't try to pawn off whatever is being marketed at the moment, thinking that I won't hear the difference. '-)
The datasheet doesn't specify some performance at the lowest frequencies but yes, the ADA4898 appears to perform very well.
Oh, shoot, I thought it was on your SiGe process. Whoops, I'm full of incorrect info lately! (Likewise Gerhard, mea culpa)
Yes, does hit a sweet spot En and In, and seems you can drive a pretty low FB network without loading the opamp too hard (I suppose you can composite it with a buffer if you need the last n'th in lowering In).
Gotcha. The OPA1611/211 (close enough, even though apparently the comp is a little different.) is a bit over 100 Hz, not too much different curve to something like the ad711. Then again, if you can use a cheaper process to get the same ends, why wouldn't you? Most of SiGe stuff is used up in the rf/microwave region, I'd imagine? (Haven't really kept track, clearly)
I don't understand the reason you ask(ed) these questions... Of course, there are many kinds of "linearity", its just like plotting two variables on an x-y absis... Are you thinking that I was asking a wrong question regarding opamp linearity?
No, it was not really a question (re opamp linearity). May be a hypothetical question, or a claim... It is very important that you know this, so that you can give the right answer if you think the question (claim) needs an answer. I noticed that you experts think so highly of opamp, and so lowly of tube amps. I think the main critical difference is "linearity" before feedback (but you guys always talk about distortion and nostalgia, which is imho not the right answer)...
In discrete amps when we talk about individual transistors, we can get "linear amplifications" before feedback. When the loop is closed, I would think that it is a different "linearity" when you do it through feedback etc. I don't know for sure with the internal of opamps but I guess opamp is designed for multi purpose (i.e. other than audio which) which require a capability to be more linear than audio application (re bandwidth). My point/assumption is that opamp linearity is a kind of amplifier linearity after feedback...
You sure know better about electronics (an expert I would say) but I doubt you know better about psychology (such as human motives). You are relating "talking through the hat" with "Wikipedia checking"? My motive was clear and it is pure psychological...
Not really. I had 2 points: linearity and stability... You are a theorist, a university lecturer kind of thing. I'm not trying to chat. I'm not trying to show that I know electronics. But I think I know something...
You are one of the experts in this thread and I asked the question only and only after/when I noticed there are new expert showing up (the TI engineer)... But you can't answer the phenomenon exists around the perception of opamps...
Of course, you can answer it with answer like "nostalgia", "cheating", "peeking", "expectation bias" bla bla bla which is not your expertise at all, but do you really think you know the reason why not all people agree with you? Assume you were a teacher, what would be your answer if you don't have the capability to make other people understand? Bad teachers will think that the students were too stupid, but imo it is not the case.
Comparing noise spectral densities at 1Hz, the OPA1611 is at 6nV/rtHz and the ADA4989 is at about 4nV/rtHz. Yes, OPA1611 is on a SiGe process but it is likely running the input devices at a lower current density than ADA4898 which helps some with low frequency noise. Just comparing Iq: 7.5mA per channel for the ADA4898 vs 3.6mA per channel for the OPA1611, likely indicates a higher tail current in the ADA4898 (doesn't guarantee it though). Input capacitance on the OPA1611 is also higher which might indicate our input devices are bigger, but this can depend on a lot of other factors as well (process type, input topology, etc.)
Lot's of ways to "skin the cat", it's why we'll be making new op amps for years to come 🙂
You are right, the linearity of open loop op amps can be quite bad. Of course,
they are not intended to be used that way (then they're called a comparator).
See p.60 here: http://www.kelm.ftn.uns.ac.rs/literatura/mpi/pdf/Op Amp Applications Handbook.pdf
See AN-1485 here: http://www.introni.it/pdf/Bob Pease Lab Notes Part 9.pdf
Also, http://www.ti.com/lit/an/snoa737/snoa737.pdf
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Thanks for the free readings, I think I need to print the above one, to avoid file lost in computer change and harddisk failure.
"They are not intended to be used that way". "Opamps can be made stable" and all kind of statements that we can all read in books... The real question is, where is the implementation where the opamp is 100% stable and implemented properly?
Look at the circuit used in the blind test done by Mooly. Isn't it designed by Douglass Self? But okay, Self uses 5532 might probably not fast enough, but with 4562 don't you think that at leas stability compensation cap should be used? The FACT from my perspective is, the amp with 5532 or 4562 has always been at the bottom of my preference list... But experts always say:
Yes, "fantasy" and the likes. Because you don't know what I know. If you think you know, EXPLAIN why I can clearly hear the difference and why FoobarABX can support what (I think) I hear? If it is an expectation/confirmation biases in my part, impossible an ABX software will validate it.
Deficient reading comprehension, most probably. But you tell me WHO don't have critical thinking ability. At least, I'm not confused of the issue. You are.
Oh absolutely, all kinds of different design choices and compromises even if the basic topology doesn't vary dramatically. But, then again, we've certainly never had it better.* 🙂 It makes a lot of our opamp choices pretty arbitrary, especially line-level, which of course lends one to conversations like this (but, of course, use whatever logic you wish to pick one that makes you happy).
*(Except maybe ready access to more inexpensive low-noise p-jfets, but I digress!)
In regards to end-to-end linearity of a monolithic opamp, it's kind of meaningless for us end-users, no? That's not to say it isn't pretty darn good (go have a look at Samuel's data at 60 dB noise gain, which eats pretty hard into the amp's respective loop gain budget), but, really, we should evaluate the end product in light of its application. Leave the local feedback of the internal gain stages versus outer loop for the folks that do this stuff professionally.
Oh, and Jay--add this one to your list. 🙂 http://web.mit.edu/6.101/www/reference/op_amps_everyone.pdf
But really, the application notes and guides from all the biggies are very very good learning resources. We're lucky to have them at our disposal.
Chris, before you start using such strong language, not sure if you followed the op amp listening test conducted in this thread. If not, it started with post #761 by Mooly, back on page 77. Under the conditions of that test, some people did hear some very small differences between op amps. The people who did hear differences included a few who previously made statements similar to yours.
That TI Op amp book you linked to is excellent - I've had that on my iPad for a few years as well.
You are right about the resources available - lots of very good stuff.
You are right about the resources available - lots of very good stuff.
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