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Comment by pclmulqdq | Hacker News Reader

Ultra-precise resistor values have been possible for as long as there have been good meters. It turns out that's a very long time ago.

The numerology makes a lot of sense if you are working with 0.1% tolerance parts. Lower tolerances have actually gotten more popular as electronics have become more cost-sensitive.

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> Ultra-precise resistor values have been possible for as long as there have been good meters. It turns out that's a very long time ago.

It's not about metering but stability of the resulting value. 1% or 0.1% doesn't do you much good if few degree temperature change gets it out of spec. Now temperature coefficent is an additional spec on the spec sheet but by definition you kinda need low drift to go in pair with high precision

> The numerology makes a lot of sense if you are working with 0.1% tolerance parts. Lower tolerances have actually gotten more popular as electronics have become more cost-sensitive.

Lower tolerances have just become cheap. Back when I was a kid there was significant difference in price between 1% and 5% resistors. Now they cost basically same (for low power ones at least) so why not ? [1]

You also don't really need that many precision parts in the first palce.

Where before in say a power amplifier you had say an analog preamp driving power IC (or outright discrete power amplifier) you had to have a bunch of precise resistors (or someone tweaking a pot on the production line) to keep the gain same in both tracks. Now you just slap a D-class chip that takes line in and outputs power and you're done, and the few % variance in power supply caps or output filter doesn't matter much.

* [1] https://eu.mouser.com/c/passive-components/resistors/?case%2...

On price - you are looking at low quantity. Buy a few million of them from a manufacturer, and you will find the 5% ones still significantly cheaper (even at standard temp coefficients and power levels). That's why new 5% and 10% resistor products are still sold.

Note that the second part of the argument was that the quantities needed are low. I'd go even further than the GP: even in the "old days" my understanding is that the number of precision parts needed was very low. Most circuitry is of the "pick a component value in this order of magnitude" variety, even on sensitive hardware. Only the handful of parts where it really matters need precision.

But, whereas previously you might spec 5% for a few resistors and 10% for the bulk, now it's no longer worth the added line on your BOM.

> Buy a few million of them from a manufacturer, and you will find the 5% ones still significantly cheaper

That just ain't true. 5% are not really used (at least with consumer electronics). 1% and 5% difference is very tiny, even across few millions.

> That's why new 5% and 10% resistor products are still sold.

If you go on digikey and search for 10% you will not find very many compared to 1%

> you had to have a bunch of precise resistors (or someone tweaking a pot on the production line) to keep the gain same in both tracks

Or match them by hand before they’re placed.

But if you need 0.1% tolerance resistors and the circuit diagram requires a 13.3 (±0.1%) kΩ resistor, you can just order one ...?

I have a hard time imagining situations like "We need a very precise 57kΩ (±0.5kΩ or about 1%) resistance but we can only get three precise resistors: 10kΩ, 22kΩ, and 47kΩ! Oh thank god we can connect 10kΩ and 47kΩ, if the last one was 46kΩ we would have been in trouble."

In terms of scale, you cannot simply order a larger factory. It has opportunity cost.

There are a lot of times when even the 1% and 0.1% ladders don't have the value you need, and you can usually construct a combination of only two of them to get that value, thanks to the way the ladders are set up.

Possible, sure, but isn't the origin of the E12 series, as opposed to using e.g. the Renard R10 series, for specifying ±10% precision parts?

1 ±10% is 0.9 to 1.1

1.2 ±10% is 1.08 to 1.32

1.5 ±10% is 1.35 to 1.65

1.8 ±10% is 1.62 to 1.98

2.2 ±10% is 1.98 to 2.42

And so on.

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