Opinions: On op amp replacement

[Buck Buchanan]

At 12:56 PM 1/29/99 +0100, Martin Czech wrote:
>The 5532 has quite high input leakage and bias currents, also offset
>voltages. Replacing a TL071 with one 5534 won't work in applications with
>high signal impedance, eg. filter cap buffer, integrator.  You introduce
>a lot of offset (very temp dependend and source resistance dependend)
>and leakage in your circuit. The 553x series is for standard audio signal
>path, ie.  no leakage and no offset requierement. Then you can benefit
>from it's high bandwidth and low nois like you pointed out.


I'll have to second that.  I love the 5532 for audio paths where you don't
mind a lot of offset.  Not a terribly good choice for CV paths.  I seem to
remember these guys sucking down approx 4 mA so watch your current (I've
had to reluctantly leave them out of batter powered devices for this
reason).  The LF412 is an excellent dual with very low drift and offset -
good for CV paths however the OP07 is still much better (though only a
single w/same pinout as 741).

Original poster said:
>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...?

Low drift guys will improve stability in CV paths.  Low noise guys will
improve noise in audio paths.  *How much* difference is hard to define but
on a good instrument, I'd say it's worth doing *IF* there's a performance
parameter you really want to improve.  For example:  It might not be worth
messing with the LFOs or EVs at all while the VCOs could benefit from low
drift parts and the filters from low noise parts.  The 741s are great to
use when you specifically want a "slow" op-amp (people use 'em in triangle
shapers to help remove glitches).

Have fun!!!!

Buck