[sdiy] op amps [was: Re: TI SN74LS624N, worth buying?]

[Magnus Danielson]

On 11/13/2011 07:33 PM, Lanterman, Aaron wrote:
>> On 11/13/2011 03:19 PM, John Alex Hvidlykke wrote:
>>> Op-amps are the workhorses of audio electronics, but they come in a
>>> confusing lot of versions. That the 072 and 074 are almost omnipresent I am
>>> aware of. But how good are they, compared to other "standard" op-amps? In my
>>> box of amps I have several 741's and 1741's, which, as far as I am concerned
>>> must be the lowest in the range. Do the 07x compare to them, or are they
>>> much better/faster?
>
> One bit of warning - don't necessarily always assume you can replace a 741 (or similar cruddy op amp by modern standards (with a better one). One or two of my students have come across cases where the slow slew of the 741 helped prevent parasitic oscillations - a TL07x in the same spot in the circuit would yield these crazy ultrasonic oscillations that sticking in capacitors wouldn't tame. (This doesn't seem to happen too often, though.)

True, but some circuits are even more sinister, they can depend on the 
internal design of the 741 such that it will just not work. Jürgen had 
that experience for instance. The 741 was once the ubiquitous choice, 
limited but lots of effort was put into take it way outside it's 
limitations. Taking such a design and "improve" it without understanding 
the role the 741 had in it can be difficult. But even simple circuits 
can require some redesign if not using the 741s, but most of them can be 
about adding a cap in the feedback path to remove risk of oscillation.

So, upgrading an old circuit can be done, but it come with a number of 
risks which needs to be managed. You run into risk of learning things 
the hard way, so your milage may vary.

Over time, things like DC stability has also improved, and there are 
some op-amps which is really good for DC gain applications. If you 
really care about it, then choosing that is good.

There is tons of knoweldge just in the history of this email-list, so go 
and search it.

Cheers,
Magnus