Opinions: On op amp replacement

[Bissell, Harry]

741 and 1458 op amps have a nice property... the will not latch up if
overdriven. Many very good op-amps have a problem where the output will go
the the negative supply when overdriven positive, and vice versa. They will
also STICK there for an extended period of time after the removal of the
overdrive.
	This is the absolute kiss of death if you are trying to make a
'temperature control loop' and must be guarded against. (see the Jim
Williams chip heater circuits, etc.) Now who would want to make a chip get
hot, anyway ?  ;-)   Harry.

> -----Original Message-----
> From:	jhaible [SMTP:jhaible at primus-online.de]
> Sent:	Thursday, January 28, 1999 3:40 PM
> To:	synth-diy at mailhost.bpa.nl; i.c. ultramedia
> Subject:	Re: Opinions: On op amp replacement
> 
> > I was recently given the advice to replace all the 741 and 748 op amps
> (on
> > a paia modular)
> > with LM301AN's, and LF351N's--------
> > 
> > 2 questions.
> > 
> > 1--Anyone have opinions on *how much* difference this might make?
> They're
> > relatively cheap (1.10 usd or so) and direct pin-compatible, I've been
> > told, but I'll need about 20, so thought I'd ask.
> > 2--Any good projects with which to use the 741/748s that will be left
> over,
> > or are they that useless...?
> > 
> > 
> > Thanks gurus, for the thoughts...
> > 
> > charles morpheus
> > icumedia
> > 
> > >I also found that if you change all the 748 op amps to LM301AN's, and
> 741
> > >op amps to LF351N's that the system becomes much quieter and more
> stable.
> > >Apparently the 741's and 748's, are the worst op amps you can get, and
> buy
> > >changing them to newer, higher quality op amps, improves performance
> > >dramatically (I got this info from a former ARP tech).
> 
> There is no general answer unless somebody is familiar with the whole
> circuit in question.
> As a matter of fact, you can replace these opamps in *many* cases, but
> there are
> exceptions. There are circuits that rely on the low slew rate of an opamp
> to smooth
> glitches, there might be stability problems with a faster opamp in
> general,
> and
> the input common mode range of a 741 goes down to lower voltages than a
> JFET
> input opamp would. I have even seen pin 3 of a 741 being tied to the
> negative rail
> (not gnd !), and the whole thing still working as linear inverting
> amplifier with a
> feedback loop comprising an external transistor. (That's the MK 2 VCS3,
> btw.)
> 
> If you keep these exceptions in mind (are there more ?), you can probably
> decide
> which opamp can savely be replaced and where to be careful. I'd suggest
> exchanging
> them one by one, and not all at one time, if you are not sure. I'd leave
> opamps
> that are part of the power supply alone. (There are PSUs with a 723 for
> positive, and
> an opamp for negative rail.)
> 
> JH.