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Noob question on resistor tolerance
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Noob question on resistor tolerance
zorglub76
Hi all,

I'm pretty new to both Eurorack and electronics. After two successful builds (Befaco's Rampage and Instrument interface), I started building Erica Synths Polivoks VCO II. There I found resistors with 0.1% tolerance.

1. Does this mean that I can get e.g. 1% tolerance resistors that are spot on (100.0 kOhm) and use them?

2. Does stated tolerance also mean that during the use, resistance would change in 1% or 0.1% margin (because of changed temperature, or something like that)?
LoFi Junglist
The tolerance marked on the package indicates the precision in manufacturing, It does not indicate quality.

Please note in some circuits the values are quite critical (voltage biasing circuit etc), whereas in other parts (for example a 'pull up' or 'pull down' resistor) the exact value is not critical at all, and a 5% or even 10% tolerance resistor would have no impact on the function of the circuit.

Most capacitors have 20% tolerance by the way sad banana

buy what you can afford, precise components are getting cheaper and cheaper every year thumbs up
zorglub76
@LoFi Junglist - that means that if I need 100k 0.1% resistor, I can measure resistance of the resistors that I have in my bag, and if one of them is in 99.9-100.1k range, I can use it?
LoFi Junglist
zorglub76 wrote:
@LoFi Junglist - that means that if I need 100k 0.1% resistor, I can measure resistance of the resistors that I have in my bag, and if one of them is in 99.9-100.1k range, I can use it?


Theoretically yes, but your average consumer DMM should not to be trusted with that type of precision.
zorglub76
Ok, thanks!
mskala
Testing and selecting 1% resistors to find the ones that happen to be within 0.1% and using those is fine if, as LoFi Junglist said, you are actually able to measure them down to that level of precision. This is often how manufacturers produce the 0.1% resistors in the first place.

However, two points:

Because manufacturers do test and select wide-tolerance resistors to get the narrow-tolerance ones, it is possible that from some manufacturers, the resistors sold as 1% won't include very many that just randomly happen to be 0.1% tolerance, because those have been pulled out to be sold at higher prices as 0.1%. Usually not a huge problem, because they sell so many more 1% than 0.1% that they won't really be pulling out a large fraction to sell at the higher price. But it is at least possible. You can't assume that resistors sold as 1% will have a bell-curve distribution with a lot of them near the exact value or anything like that.

Temperature and age-related resistance changes do occur and if you're concerned about them you need to look for the specifications on those things separately. These usually have more to do with the type of resistor (i.e. what substance is used to produce the resistance) rather than the tolerance. If you're looking at 1% and 0.1% they'll probably both be metal film and have similar aging and temperature specs, but if you're looking at a 5% resistor it'll probably be carbon film and have different temperature and aging compared to a metal film 0.1%. I wouldn't substitute a 5% carbon resistor for a 0.1% metal film even if it did happen to have exactly the right initial resistance value; it will age and respond to temperature differently.
Synthiq
mskala wrote:
I wouldn't substitute a 5% carbon resistor for a 0.1% metal film even if it did happen to have exactly the right initial resistance value; it will age and respond to temperature differently.

Yes, a metal film resistor has a temperature coefficient of +/-100ppm/C or better while carbon film resistors seem to have a temperature coefficient of around -1100ppm/C, so the latter can change 0.1% per degree C! This also mean that metal and carbon film resistors shouldn't be mixed if the circuit must be stable over temperature. Presumably this would apply to mixing carbon potentiometers and metal film resistors as well, but I have yet to find a carbon potentiometer datasheet listing the temperature coefficient of these so I can only guess.
Koa
Lofi and mskala make the lion's share of points one needs to consider when dealing with this question.

If you're working with thru-hole configurations, do note that film has its disadvantages in which larger values tend to get too large for ergonomic fit. Therefore the other types of electrolytics still have their place. Same goes for tantalum etc.

MLCC is coming onboard to deal with many of the problems of those and others most deem inferior to the current gen component archetype.
Koa
My first love was modding guitar pedals. That moved me to seek building my own pedals from DIY schems and kits. Aion Electronics' resources were valuable to me while I was starting out. Check this out for a good primer on not only what the different types of each component are, but practically speaking, where to source them for best quality and value.

https://aionelectronics.com/resources/where-to-buy-what/
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