Bottlehead Forum

General Category => General Discussion => Topic started by: pro_crip on March 19, 2011, 04:27:53 AM

Title: matching resistors to a schematic value
Post by: pro_crip on March 19, 2011, 04:27:53 AM

This isn't really a tube question, more of a mathematical analysis. How many resistors would I have to buy to guarantee that a pair of them will perfectly (within 4 significant digits) match the value called for in the schematic? This is what I get for depending on excel too much. Thanks for listening.



Rich

Title: Re: matching resistors to a schematic value
Post by: Paul Joppa on March 19, 2011, 05:39:16 AM

Quote from: pro_crip on March 19, 2011, 04:27:53 AM

... How many resistors would I have to buy to guarantee that a pair of them will perfectly (within 4 significant digits) match the value called for in the schematic? ...

This is a statistical question. The answer is an infinite number; the best you can do is improve the probability that a pair will match - no guarantee is possible.

You are asking for 0.01% accuracy. On average I think you have a 50% chance that one out of a hundred 1% resistors will match a given value to 0.01%, so there must be a 25% chance that two out of 200 will do so. Beyond that, I don't remember enough of my probability and statistics education to answer.

You can buy 0.1% resistors pretty readily, but only in selected values.

Title: Re: matching resistors to a schematic value
Post by: STURMJ on March 19, 2011, 08:06:02 AM

Part Connexion carries prp resistors. They advertise 1% but the site says they may be closer to 0.1% . They are not expensive either, and they are made here in the mid-west USA!