[sdiy] Ratio switching!

[Needham, Alan]

On 24 May 2007, at 09:47, Louis van Dompselaar wrote:
~~
~~ > But in practice you might end up with thousands of +1% resistors in  
~~ > one batch and thousands of +2% in the other and never get the  
~~ > division you want.
~~
~~The final thing is that given that resistors only come in certain  
~~values (E24 or whatever) the accuracy of the ratio is going to depend  
~~on finding a good pair of resistors to create that ratio. For certain  
~~musical ratios, this could be an issue.

Given that I am now ignoring temperature stability, which may or may not actually be self-cancelling accross the divider,

Given the scenario of a 16k resistor which tests as +2% (16,320 Ohms), a parallel resistor of 816k would correct it to spot-on.
If the nearest E24 value of 820k (which is accurate) is used then the parallel combination would give 16001.5 Ohms, +0.01% error ?

OK, so a simple divider may have just become three or four resistors, but it's not going to cost a fortune...

	Alan

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