Opinions: On op amp replacement

[Bissell, Harry]

The 3140 could have the diode leakage problem solved with external diodes in
series with the supplies, (but why bother). For Audio, the 3140 (correct me
if i'm wrong) Sucks (poor noise performance) ! For a sample and hold though,
it is an excellent choice. BUT watch out for the non-symetrical sourece and
sink current. It can source 10mA, but sink 1mA. Put that into your
capacitive load and smoke it...  ;-) harry

> -----Original Message-----
> From:	Martin Czech [SMTP:martin.czech at intermetall.de]
> Sent:	Friday, January 29, 1999 8:26 AM
> To:	jorgen.bergfors at idg.se
> Cc:	synth-diy at mailhost.bpa.nl
> Subject:	Re: Opinions: On op amp replacement
> 
> I'd say:
> 
> LF41x    etc. for low offset and offset drift, rel. low leak
> NE553x   for high bandwitdh, low noise
> TL07x    for rel. low noise, low leak
> CA3140   low leakage
> TL08x    else
> 
> I really would like to test "very low" leak types like CA3140
> against TL07x or LF041x.
> 
> The 3140 has mosfet inputs, but ESD-Protection diode junctions as well,
> if Ta max is set to 45C, how much more leakage would a 41x or a 07x 
> take ? Is it really an order of magnitude ? I doubt. 
> And the data sheet also. And the 3140 has certainly a lot of
> disadvantages.
> 
> Old schematics (and our concepts are all very old) suffer from the fact,
> that at THAT time no other ICs existet. Today one should consider using
> something better.
> 
> Of course, a clone is a clone, better stay to original hardware then.
> 
> But: semiconductor manufacuturers change masks without notice,
> it is very doubtfull if a 1978 3140 is really the same as some 3140
> from today, even worse with second source products.
> 
> Circuits that rely on parasitic effects may not even work
> with todays hardware, even if the stamp code says "3140".
> 
> m.c.