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From: Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>
Newsgroups: sci.electronics.design
Subject: Re: The Venerable 741
Date: Sun, 3 Nov 2024 20:14:04 -0000 (UTC)
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john larkin <JL@gct.com> wrote:
> On Sun, 3 Nov 2024 19:14:54 -0000 (UTC), Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
> 
>> john larkin <JL@gct.com> wrote:
>>> On Sun, 03 Nov 2024 18:07:35 +0000, Cursitor Doom <cd@notformail.com>
>>> wrote:
>>> 
>>>> It's been around an awfully long time and there are far better
>>>> alternatives out there. But is there still a case for using them in
>>>> certain niche applications in 2024? 
>>> 
>>> I can't think of one. The design is 56 years old. It has its own
>>> Wikipedia page.
>>> 
>>> There are faster, cheaper, lower noise, lower bias current/offset RRIO
>>> amps around these days.
>>> 
>>> I remember the day when, still a kid in college, I decided to replace
>>> LM709s with LM741s in a control system. The 741s were more expensive
>>> (the cost of a pretty good lunch) but didn't need external
>>> compensation parts or front-end-zener protection, and current limited.
>>> 
>>> The early 741s had bad popcorn noise, but I'd expect that to be better
>>> now.
>>> 
>>> My default gumdrop amp is OPA197 now, in SOT23. It makes a good
>>> comparator too. There are cheaper parts if you can tolerate low supply
>>> voltages.
>>> 
>>> 
>> 
>> LM358s are still useful, though.  I use them in things like bias loops,
>> where their limited speed and fairly poor input accuracy don’t matter. 
>> 
>> In our licensing conversations, pointing out that we’re saving more on the
>> BOM than the royalty costs is a pretty persuasive argument, entirely aside
>> from the improved performance. 
>> 
>> Cheers 
>> 
>> Phil Hobbs 
> 
> 358 is not bad, a dual opamp for 10 cents, but most have some shared
> current sources that can make sections interact. And weird behavior if
> any input goes slightly below ground.
> 
> 

AFAICT it was just the original 324 that had the shared current source
problem. I’ve never run into it in any 358 or 324A version. 

The problem is pretty unsubtle, though. Pulling both (PNP) inputs of any
section high enough causes its tail source to saturate, so its beta tanks
and it sucks all the available drive, turning off the input stages of the
other 3 sections. 

There are all sorts of Chinese parts on LCSC that are even cheaper and
apparently better, but the 358 is a known quantity, which matters a lot. 

Cheers 

Phil Hobbs 
-- 
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics