Choosing an op-amp for your project
lcamtuf.substack.com
Choosing an op-amp for your project
1–10 of 90 posts
Re: Choosing an op-amp for your project
#2Great write up. And definitely skip the 60 year old models.
Also valuable to look for is ESD protection. Many op amps have good 2kV static shock protection. Really sucks to have cascading failures due to touching your circuit and blowing an op amp.
For some uses it’s also good to checkout input current bias.
Re: Choosing an op-amp for your project
#3Great write up. And definitely skip the 60 year old models. Also valuable to look for is ESD protection. Many op amps have good 2kV static shock protection. Really sucks to have cascading failures due to touching your circuit and blowing an op amp. For some uses it’s also good to checkout input current bias.
Another bit I discovered is the quality of resistors. Pretty much any op amp circuit will use resistors. Often the resistors limit the static offsets.
Don’t stick with 1% for analog circuits as 0.1% precision resistors are cheap and come with low temp drift as well.
Re: Choosing an op-amp for your project
#4To add to this discussion is useful the video or eevlog: https://www.youtube.com/watch?v=uq1DMWtjL2U
where Dave discusses the "Jelly bean" op amps
Re: Choosing an op-amp for your project
#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.
Re: Choosing an op-amp for your project
#6>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
Re: Choosing an op-amp for your project
#7I'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, you have a ceiling for how much your total BOM can cost before you've priced yourself out of competition.
In the end, a 8.7x cost bump is a lot to swallow for a feature that most consumers are physically incapable of distinguishing between. Every time I've raised the possibility of using the fancy new chips, vastly more experienced engineers than me have come out of the woodwork to tell me that in almost all scenarios, the tradeoff between price and quality isn't worth it.
Of course, if budget is not an issue, use the OPA2323. It really does sound great. Or more accurately, the degree to which it destroys good sound is as low as we can currently achieve.
(This comment originally stated a 12x factor, but I was terrible at math.)
Re: Choosing an op-amp for your project
#8I 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 looking at opamps as alternatives to the LM324 and found some interesting-sounding parts, in particular for a poor man's SMU application (precision, low current, and voltage requirements, but not much bandwidth). Haven't tried any of them yet. Comments would be welcome.
- LM324B: TI's improved LM324, with half the input offset voltage and otherwise improved ratings, and just as cheap, but still bipolar.
- OPA4197 and family: three dollars but it's a quad RRIO 36V 10MHz opamp in a 14-SOIC with ±15nA input bias current, ±100μV max input offset voltage, and 120dB min CMRR. The datasheet makes it sound amazing for the price. The OPA177 seems like it would be better but pricier.
- OP4177ARUZ: a 16-dollar quad 36V 1.3MHz opamp with ±2nA input bias current, 75μV max input offset voltage (at ±15V power supply), and min 120dB CMRR
Then I decided I'd screwed up my design sketch by requiring one of the opamps to sink significant current very close to the negative rail, which is something even "rail-to-rail" opamps can't do; I was planning to use millivolts from ground to represent measured nanoamps. If you want to look at a simulation with idealized opamps, it's at https://tinyurl.com/2aomvpn5, but don't take it as exemplary in any sense; it's a novice design with novice mistakes (and I would be grateful in the unlikely case that someone took the trouble to point some of them out). I think I need to redesign the circuit as a bipolarity-supply circuit or something, or use a differential output for the current measurement, or rethink it entirely.
Re: Choosing an op-amp for your project
#9I'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…
Is the cost delta really 12×?
Looking at Mouser Canada, it looks like the cheapest 071 is the TL071CDR, at $0.138/each (Canadian) in quantities of 5k. The OPA2323IDDFR is $0.49 in the same quantity.
> In the end, a 12x cost bump is a lot to swallow for a feature that most consumers are physically incapable of distinguishing between.
I think that the performance of an op-amp should very rarely have user-visible effects. The more interesting question is whether the more expensive chip can make for a simpler design elsewhere. For example, can a rail-to-rail amplifier save the extra cost of needing charge pumps and split-rail design elsewhere?
Also, not all domains should be cost-optimized. Hobbyist or prototyping work might best benefit from using a more expensive but more capable amplifier as a first choice, saving on the number of components that might need to be stocked in the home lab.
Re: Choosing an op-amp for your project
#10I'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…
Is the cost delta really 12×? Looking at Mouser Canada, it looks like the cheapest 071 is the TL071CDR, at $0.138/each (Canadian) in quantities of 5k. The OPA2323IDDFR is $0.49 in the same quantity. > In the end, a 12x cost bump is a lot to swallow for a feature that most consumers are physically incapable of distinguishing between. I think that the performance of an op-amp should very rarely have user-visible effect…
All good points! And I am no expert.
FWIW, here is what I was going off of, price wise:
https://www.digikey.ca/en/products/detail/texas-instruments/...
https://www.digikey.ca/en/products/detail/texas-instruments/...
In other words, the cheapest TL071 variant and the cheapest OPA2323 variant on Digikey Canada, in a quantity of 1 (ie wildly expensive). $0.31 vs $2.70 means that I shouldn't attempt math before coffee; 8.7x is still a big bump, although I acknowledge it's not the 12x I disinformationed earlier, with apologies to anyone reading.