[sdiy] Op amps (was Re: TI SN74LS624N, worth buying?)

[David G Dixon]

> The TL series are more modern but still pretty old. We'll be 
> generous and say "classic". You'll find them inside any of a 
> million synths and amps and such like from the last thirty years.
> It was my understanding that the 08x were low DC offset, the 
> 07x were low noise, and the 06x were low current. All 
> basically the same chip, but optimised for difference 
> characteristics. I never used the 081/082/084 much, but I 
> used to use the TL064 in guitar pedals because it gave a much 
> better battery life than the others.

Hey John, welcome to Synth DIY Addicts Anonymous!

I notice that a lot of circuits specify TL07x for CV signal processing and
TL07x for audio signal processing.  I have never used TL08x, personally.  I
tend to use TL07x for everything, and primarily the quads when I can -- I
know, terrible, just terrible! -- and yet, my modular is very quiet in a
quiescent state, and people comment on how "hi-fi" it sounds.  Plus, we have
used TL07x almost exclusively in the Intellijel eurorack modules based on my
homebrew designs, and these are getting rave reviews on Muffs.

However, it is interesting to compare the TL07x and TL08x datasheets.  TL07x
is supposed to be less noisy, and yet they share identical noise specs --
18nV/root(Hz) at 1kHz and room temperature.  Indeed, the only difference I
can see is that the TL08x has slightly better input bias current specs (30pA
typical, as opposed to 60pA typical for the TL07x).  It also looks as if the
lowest-grade TL08x is a little rougher, spec-wise, than the lowest-grade
TL07x, but they seem to be more or less identical in the higher grades.  If
there are other differences, I'm not seeing them.  Perhaps someone with less
datasheet-induced ADHD can point them out!  :)

Of course, they are both dirt cheap, and this is also a major factor.