[sdiy] TL072??

Tim Ressel timr at circuitabbey.com
Thu Jun 12 09:26:23 CEST 2014


Op amp swaps: A cautionary tale

One fine day a production item starting failing in droves during production test. An opamp was popping. I forget the type. It turns out the circuit would momentarily drop an input below the negative rail. The NS parts would handle this just fine, but we switched to an ST part, which could not. A protection diode fixed the issue.  Admittedly we were violating a spec sheet value; slap our wrist. But it was a surprise that the robust NS part handled it. 


Engineering: No place for wimps


Tim Ressel
Circuit Abbey
503-750-9331
timr at circuitabbey.com




________________________________
From: David G Dixon <dixon at mail.ubc.ca>
To: 'Dan Snazelle' <subjectivity at hotmail.com> 
Cc: 'Tim Ressel' <timr at circuitabbey.com>; 'Synth-Diy' <synth-diy at dropmix.xs4all.nl> 
Sent: Thursday, June 12, 2014 12:08 AM
Subject: RE: [sdiy] TL072??


In my opinion, the tiny differences I saw in the datasheet between TL07XC
and TL08XC (the only grades where there were differences in anything except
CMRR) would never be noticed in any normal application.

I still say they are interchangeable.



> -----Original Message-----
> From: Dan Snazelle [mailto:subjectivity at hotmail.com] 
> Sent: Wednesday, June 11, 2014 11:46 PM
> To: David G Dixon
> Cc: Tim Ressel; Synth-Diy
> Subject: Re: [sdiy] TL072??
> 
> david... i see here you said two things which relate to the 
> question of What the differences are between the two opamps
> 
> at first i thought you said they ARE interchangeable ( which  
> for me means you can safely switch them on a BOM with no 
> detrimental effects )
> 
> but then I saw that before that you did a great job of 
> listing the three "small" differences some of which you said 
> are in the cheaper versions (which many people use) 
> 
> but those small differences can matter in situations where 
> those specs were crucial to something working : current draw 
> limited situations, repair situations or people ordering kits 
> which ask for 82s or 72s ( i would never want a population 
> place to switch 72s to 82s or vice versa as that is throwing 
> enough difference into a circuit which might use 5-10 tloxx 
> chips...which could cause sub-optimal operation
> 
> and since they are all so low in price, i always keep 72s and 
> 82s on hand (and of course 62s)
> 
> i guess i just wanted Tim to know that there is definitely 
> SOME difference thats all
> 
> 
> 
> funnily enough, tonight I stumbled across a repair techs 
> blog... when i found someone else who has had issues helped 
> by switching from 72s to 82s ...ultimately he went to a 62 
> but i think it gives more credence to the idea that 72s and 
> 82s are not always exactly the same.
> 
> anyway its a funny anecdote about why keeping all three 
> around is useful! ( well we all know 62s are great for many 
> apps anyway)
> 
> korg polysix repair: 
> 
> Another day dawned, and the keyboard was taken out once again 
> to allow test equipment access to the oscillator section. 
> Apart from the K30A O FET, everything in voice 5 was brand 
> new but also of the original type. In a moment of desperation 
> we replaced the TLO72 with a TLO82 just to see what 
> difference it made.
> It did make a difference, voice 5 was now sharp, we thought 
> great, trim it down and job done.
> Not so, when voice 5 was flat, the tune low trimmer ran out 
> of track before tuning was achieved, when it was sharp the 
> same thing happened at the other end of the trimmer.
> We next tried a TLO62, and in a Goldilocks moment, it was just right."
> 
> 
> (from here:
> http://retroactivesynth.com/index.php?page=march-2011
>    
> 
> Sent from my iPad
> 
> > On Jun 11, 2014, at 3:54 PM, "David G Dixon" 
> <dixon at mail.ubc.ca> wrote:
> > 
> > The slew rate specs are identical for 8X and 7X.  The input current 
> > specs are actually a little better for 8X.  All the other specs are 
> > more or less identical, except that the very lowest grade 8X are a 
> > little lower than the lowest grade 7X on the input voltage 
> specs, and 
> > the CMRR spec for 8X is slightly lower generally (86dB vs 100dB).
> > 
> > Verdict: they are interchangeable.
> > 
> > 
> >> -----Original Message-----
> >> From: Dan Snazelle [mailto:subjectivity at hotmail.com]
> >> Sent: Wednesday, June 11, 2014 9:11 AM
> >> To: David G Dixon
> >> Cc: Tim Ressel; Synth-Diy
> >> Subject: Re: [sdiy] TL072??
> >> 
> >> they are not always interchangeable
> >> 
> >> at least not in terms of certain applications.
> >> 
> >> i can think of at least one case of my own and im pretty 
> sure others 
> >> have told me of cases where they needed an 82 vs 72 or 
> vice versa. ( 
> >> my instance was involving a product of mine and in the BOM 
> there is 
> >> an 82) where a. 82s (poorer?) performance versus the 72 was more 
> >> desirable.
> >> 
> >> (it was in an lfo btw)
> >> 
> >> however this was NOT based on a noise consideration but, I seem to 
> >> recall (this was waaaay back in 2009) based on either slew or 
> >> current.
> >> 
> >> 
> >> maybe verbos can remember ?
> >> 
> >> 
> >> best
> >> 
> >> 
> >> 
> >> 
> >> Sent from my iPhone
> >> 
> >>>> On Jun 11, 2014, at 12:23 AM, "David G Dixon"
> >>> <dixon at mail.ubc.ca> wrote:
> >>> 
> >>> I think they're interchangeable. 
> >>> 
> >>>> -----Original Message-----
> >>>> From: synth-diy-bounces at dropmix.xs4all.nl
> >>>> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of
> >> Tim Ressel
> >>>> Sent: Tuesday, June 10, 2014 9:04 PM
> >>>> To: Synth-Diy
> >>>> Subject: [sdiy] TL072??
> >>>> 
> >>>> Hi,
> >>>> 
> >>>> Someone please explain to me the difference between the
> >> TL072 and the
> >>>> TL082. I keep hearing about its low noise, but according to the 
> >>>> datasheets the noise is identical, as is the input 
> offset current.
> >>>> The input bias current is actually higher on the TL072.
> >>>> 
> >>>> I don't get it.
> >>>> 
> >>>> 
> >>>> 
> >>>> Tim Ressel
> >>>> Circuit Abbey
> >>>> 503-750-9331
> >>>> timr at circuitabbey.com
> >>>> _______________________________________________
> >>>> Synth-diy mailing list
> >>>> Synth-diy at dropmix.xs4all.nl
> >>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> >>> 
> >>> _______________________________________________
> >>> Synth-diy mailing list
> >>> Synth-diy at dropmix.xs4all.nl
> >>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> >  



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