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Choosing an op-amp for your project

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Re: Choosing an op-amp for your project

#31

Post by ckocagil »

bratwurst3000 wrote: post #6
perriera wrote: post #5

>f you’re designing a new op-amp circuit, here are some decent, all-around alternatives made in the 21st century None of the listed opamps would be an alternative to where an LM324 or TL071 are typically used - low cost, 20V-30V supply, infinite/guaranteed availability. They are 5V only and cost 10x as much.

i build and repair audio electronics and the tl071 is used in abundance in audio circuits and is a bad choice imho. But good opamps for audio are at least a few dollars

For any consumer use to play back audio I can't image a scenario where TL071 wouldn't be enough. And you'd rarely even need an op-amp when integrated solutions are available.

Re: Choosing an op-amp for your project

#32

Post by kazinator »

peteforde wrote: post #7

I've watched the videos and agree that the OPA2323 does appear to sound amazing by subjective comparison to the TL071. However, it's not enough to say that it costs ~8.7x as much in local tokens because that doesn't reflect how much it costs as a percentage of the other components around it, many of which have a more profound impact on the outcome. This wouldn't stand as a good argument except that in many devices, y…

For good sound, NE5532.

Re: Choosing an op-amp for your project

#33

Post by kragen »

cushychicken wrote: post #30
kragen wrote: post #8

I found this post extremely interesting and informative, well above my expectations even given the eminence of its author. I'm not sure that everything in it is covered in The Art of Electronics — it's the kind of stuff the book covers, but I learned things from this post I didn't learn from the book. (But possibly it's information that's in the book that I just failed to absorb the last few times.) I was recently lo…

Oh boy you need to take another look at ToEv3 if you think this has better coverage on opamp topics. It has so much about opamps in it that it’s hard to tell you where to find it all - it’s so ubiquitous and spread out in the text. Recommend Ch5 for Precision Design and Ch8 (or 9? Can’t remember) on noise.

I didn't mean that this post was "better" overall, but rather that it contained some information I didn't see in AoE (or didn't retain). Clearly AoE's presentation of opamps is far more comprehensive.

Re: Choosing an op-amp for your project

#34

Post by [deleted] »

ckocagil wrote: post #31
bratwurst3000 wrote: post #6

Earlier quoted context omitted.

i build and repair audio electronics and the tl071 is used in abundance in audio circuits and is a bad choice imho. But good opamps for audio are at least a few dollars

For any consumer use to play back audio I can't image a scenario where TL071 wouldn't be enough. And you'd rarely even need an op-amp when integrated solutions are available.

[deleted]

Re: Choosing an op-amp for your project

#35

Post by bratwurst3000 »

Archit3ch wrote: post #12
bratwurst3000 wrote: post #6

Earlier quoted context omitted.

i build and repair audio electronics and the tl071 is used in abundance in audio circuits and is a bad choice imho. But good opamps for audio are at least a few dollars

If you want the mirror the OpAmp distortion from the original units for authenticity/character, it makes sense to use the TL071, no?

thats true. I forgot to mention i mean electronics from mid 90s onward. Even in higher class electronics. for example many of those 2000 euro upwards dj mixer use tl071 and even high end dac and soundcards.

I replaced some of them with good opas and burrbrown opamps and for me it made , even if not big, audible changes to the better. But this could be my imagination.

whatever i prefere some opamps in the range from 2-4 bucks. even if its only for the feeling…didnt measure it.

Re: Choosing an op-amp for your project

#36

Post by bratwurst3000 »

spamatica wrote: post #13
bratwurst3000 wrote: post #6

Earlier quoted context omitted.

i build and repair audio electronics and the tl071 is used in abundance in audio circuits and is a bad choice imho. But good opamps for audio are at least a few dollars

Any suggestion for a (reasonably) good and cheap one for new designs?

i like the opa2134 pa , or in general the bur brown opa, on the expensive site and on the cheap one the ne5534.

Re: Choosing an op-amp for your project

#37

Post by dragontamer »

Cervisia wrote: post #17
kragen wrote: post #8

I found this post extremely interesting and informative, well above my expectations even given the eminence of its author. I'm not sure that everything in it is covered in The Art of Electronics — it's the kind of stuff the book covers, but I learned things from this post I didn't learn from the book. (But possibly it's information that's in the book that I just failed to absorb the last few times.) I was recently lo…

Nowadays, it is hard to recommend a general-purpose opamp. Just plug the desired parameters into the search function and sort what's left by price. (Distributors like DigiKey and Mouser have somewhat adequate search functions; I usually have to go to manufacturers' web sites like https://www.ti.com/amplifier-circuit/op-amps/general-purpose... to be able to filter by all important parameters. I'm mentioning TI because…

A general purpose OpAmp is just that, your general purpose first choice.

If you know more specific information about your circuit or it's application, the. You can specialize. But general purpose OpAmps are jack of all trades with specific known weaknesses to avoid.

In most cases, you calculate the error bars and none of the errors matter, so sticking with a cheap general purpose amp is best engineering.

Re: Choosing an op-amp for your project

#38

Post by tobwen »

kazinator wrote: post #32
peteforde wrote: post #7

I've watched the videos and agree that the OPA2323 does appear to sound amazing by subjective comparison to the TL071. However, it's not enough to say that it costs ~8.7x as much in local tokens because that doesn't reflect how much it costs as a percentage of the other components around it, many of which have a more profound impact on the outcome. This wouldn't stand as a good argument except that in many devices, y…

For good sound, NE5532.

But pre-ROHS of course :)

Re: Choosing an op-amp for your project

#39

Post by kragen »

Cervisia wrote: post #17
kragen wrote: post #8

I found this post extremely interesting and informative, well above my expectations even given the eminence of its author. I'm not sure that everything in it is covered in The Art of Electronics — it's the kind of stuff the book covers, but I learned things from this post I didn't learn from the book. (But possibly it's information that's in the book that I just failed to absorb the last few times.) I was recently lo…

Nowadays, it is hard to recommend a general-purpose opamp. Just plug the desired parameters into the search function and sort what's left by price. (Distributors like DigiKey and Mouser have somewhat adequate search functions; I usually have to go to manufacturers' web sites like https://www.ti.com/amplifier-circuit/op-amps/general-purpose... to be able to filter by all important parameters. I'm mentioning TI because…

Thanks! This is very useful advice!

What I meant by "requiring one of the opamps to sink significant current very close to the negative rail" is that, if you look at the schematic, the differential-to-single-ended op-amp that measures the voltage across the current-sense shunt resistor is using 10kΩ resistors in its feedback path, and the inverting input to that feedback network might be close to the positive voltage rail, say 12V, while the single-ended output is ideally millivolts from ground. So you have 12 volts across 20kΩ, which works out to 600μA, which has to be sunk into that op-amp's output.

600μA doesn't sound like a lot, and it certainly isn't going to strain the drive strength of any op-amp IC, but in this context we're hoping for millivolt precision down near the negative rail. The OPA4197 datasheet https://www.ti.com/lit/ds/symlink/opa4197.pdf figure 14, "Output Voltage Swing from Negative Power Supply vs Output Current (Maximum Supply)", shows what you might call a gently nonlinear output impedance roughly in the 40–80Ω range depending on temperature (2–4V at 50mA), which means 0.6mA of output current works out to tens of millivolts (24–48mV using those nominal impedances). Worse, even under no-load conditions, it's rated to swing only down to as much as 25mV from the negative rail (§6.7, "Electrical Characteristics: VS = ±4 V to ±18 V (VS = 8 V to 36 V) (continued)", p. 8, "Vₒ: Voltage output swing from rail, Negative rail").

In retrospect, it seems obvious that the op-amp's output isn't going to be able to reach beyond the input rails (unless it integrates a charge pump like the LM7705 internally) and is going to have trouble getting too close to them when it's sinking any current (for the negative rail, or sourcing for the positive). Because where is that current being sunk to? You need some voltage drop to get the electrons and holes to move in the desired direction through the silicon. A small negative supply might be the right solution. Or a differential output, which would be easy.

Re: Choosing an op-amp for your project

#40

Post by buescher »

Be aware in a microcontroller design, an lm324-type op amp might outperform the on-chip ADC you’re using anyway. Even the cheapest op amps from major players are better characterized and specified on their data sheets than most microcontroller ADCs. There’s no virtue in spending other people’s money and supply chain risk to use a “better” part just because it wins a bench race or it’s newer or whatever.
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