[sdiy] RC-4558 and equivelants

[jhaible at t-online.de]

> >  Yes they are. Basically a ever so slightly improved 
> > dual 741.

"Ever so slightly" translates to "fast enough (4558) vs. 
"too slow" (741)" for audio circuits with large voltage 
swing. The ubiquitous "similar to 741" in many data sheets
can often be quite misleading. Back then, it was meant
as a feature (mostly compatible, but better), today us
audio-focussed people read "741", feel uncomfortable,
and don't read further.

> >much quieter and way better freq response try using a 
> 5532. 

This is true, but in other parameters, this is *not*
compatible with the old industry standard 741, read:
*worse*. Don't use a 5532 where input bias current
is important. Most audio circuits can be designed
such that this does not matter, but that doesn't mean
all audio circuits actually were designed that way.
So blindly replacing 4558's with 5532 is a dangerous
thing.


> just be careful of the higher current draw that the 5532 
> has on the  
> power supply - too many of these may stress the power 
> supply past  
> what it was designed for...

Exactly. 
I've seen audio circuits where the signal path was divided into
separate frequency bands, and while the upper range used the
pretty fast TL074 opamps, the lower range had LM324's.
I won't argue about the overall quality of this solution
(it is a quite famous product); I just want to point out that
there's a clever idea behind that: The 0.5V/us slew rate
of 324's was enough for the lower frequencies, and the 074's
were only used where they were really needed. And the PSU
was built to exactly fill this need (with the usual tolerances
for over- and undervoltage I would presume). Replace the 324's,
and you're in trouble.

> what do people think of the 4560 and 4580 

I'm very interested to hear about this, too.
Browsed thru an old japanese catalogue yesterday,
in search of good SIL dual opamps, and found one that
said "compatible to 4560". Any experience ?

JH.