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Op-Amp 'upgrades' - TL074 vs MC33078 vs OPA22x

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juz_ad

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I'm looking for a dual op-amp in a SOIC package to test as an 'upgrade' to the TL074. I'm using these in an exponential current source which is working adequately using the TL074 - I was just curious about what possible performance boost might be available with a better specced op-amp.

I looked at the LT1013 - but the pinout is different in SOIC.

Some of the OPA22x have also been suggested but they're much more expensive.

Can anyone comment on whether the MC33078 might be a good intermediate choice as 'better' than a TL074 but not as expensive as the OPA22x

I know that's quite a big and general question!

Thanks.

- J
 

schmitt trigger

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The way I do it when selecting opamps, is to write an Excell spreadsheet and each row list the performance parameters that are important to the application itself.

For instance, if your current source must handle high frequencies, I would put slew rate first. If on the other hand, I'm dealing with sub-microamp currents, I put low Ios parameter first.
Select as many as you require. And as part of the selection, the IC package, cost and availability may play a significant role.

Then in the columns add as many opamps from as many vendors as you want. Open up their respective datasheets, and write down the values of each performance parameter for each opamp.

It is a lot of work, but when you are finished, you'll have a nice table where you can easily compare all the requirements. Your requirements. Only you know what is needed.

I've many times offered suggestions, to have a reply of "its not available in my country", or "I can't solder SMT components".
 

KlausST

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Hi,

I looked at the LT1013 - but the pinout is different in SOIC.
No wonder TL074 is a quad OPAMP but LT1013 is a dual OPAMP ;-)
But yes, I see that the SO-8 package of LT1013 is no standard pinning. :-(

please define in what parameters you want an improvement.
--> In most cases the benifit in one parameter is a drawback in another parameter.

Klaus
 

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Re: Op-Amp 'upgrades' - TL072 vs MC33078 vs OPA22x

The way I do it when selecting opamps, is to write an Excell spreadsheet

That's exactly what I did and I don't feel like there was an obvious answer (that I could see). For example - the OPA2227 seems to be very highly regarded but it has a lower slew rate and a higher quiescent current than the TL072 - and it's nearly 20x the price!

The LT1013 is another one that's suggested regularly - extremely low quiescent current but a slew rate that doesn't appear to be that much better than the old 741!

There's already a bunch of TL072s in this particular circuit, they're operating with inputs from DC up to AC within the audio range - so slew isn't a major issue, I'm operating off a +/-12V 1A supply - so quiescent current isn't life or death… input/output offset is probably an important one so I could check that again…

…maybe I already have a perfectly adequate amp.

Gah!
 

Audioguru

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The MC33078 has about the same low noise and wide bandwidth as the TL074. But the TL074 has Jfet inputs for extremely low or no input current while the MC33078 uses PNP transistors with a certain bias current requirement.
If the TL074 biasing will work with the MC33078 then you will not notice any difference.

If your input signal level is high then the TL074 output will suddenly go high if the input voltage becomes too low or negative because it has the problem called Opamp Phase Inversion when the input voltage becomes within a few volts of the negative supply voltage.
 

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juz_ad

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Hi,
No wonder TL074 is a quad OPAMP but LT1013 is a dual OPAMP ;-)

No wonder it didn't work! :wink: Yes - my bad - I did mean TL072 :roll:

Hi,
please define in what parameters you want an improvement.
--> In most cases the benifit in one parameter is a drawback in another parameter.

I'd like to see if I can improve the 'precision' of the current source - so I guess that's down to input offset and Common mode rejection?

I should point out that the circuit is working as expected - so I'm not trying to 'fix' anything - more just seeing if I can get better performance with a 'better' amp.

Thanks all.
 

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Hi,

..you speak of audio signals.

Maybe you should take care of:
* low voltage noise
* low current noise
* low distortion
* low offset voltage
* low bias/offset current
* high GBW
* high slew rate

The later two: Example: if you want high quality audio. Distortion <0.01% at 10kHz at a gain of 5.
Then you should consider using an OPAMP with GBW more than 5MHz (just estimated. it additionally depends on internal circuitry and closed loop output impedance...)

Klaus
 

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Can you share the table you created?

Sure - here's where I'm at:



The TL072 is my current workhorse and I use the OPA2134 in critical audio applications when I need to. I'd like to find a 3rd choice for critical/precision DC circuits e.g. exponential converters - but that will also be happy handling audio if needed.

Right now - the TLE2142ID is looking like a good choice. Hefty current sourcing (one of the intended uses is as the buffer output for LM336/LM385 VRefs), good bandwidth, great slew rate, higher quiescent current than I'd like - but I think I can live with that…

Appreciate the advice.

Thanks :)
 

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Hi,

I'd like to see if I can improve the 'precision' of the current source - so I guess that's down to input offset and Common mode rejection?
Without your schematic - hard to say.

Is it for DC use, or do you expect frequency.. or voltage steps?

A constant current source, built with a FET, does not need large CMVR. I rather think that offset current and offset voltage drift can cause errors.

Klaus
 

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With that table you can easily see how come the TL072 is such a popular opamp.

Although it is a 40 year old design, yet its specs are fairly decent, and it is incredibly cheap!
And available the world over.
 

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The TL072 is cheap because it was used in so many audio products and in most of mine. Its sales are probably higher than any other opamp and is made by many manufacturers. A Japanese company (Toshiba?) made a "better" TL072 but they were all recalled because they oscillated at a high frequency.
 

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