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DIY Stompboxes => Building your own stompbox => Topic started by: Marc.yo on August 06, 2007, 03:54:30 PM

Title: Is there a way to subtract resistance w/out using an OP amp
Post by: Marc.yo on August 06, 2007, 03:54:30 PM
I don't have any OP amps and I need to get a lower resistance from a resistor, if that makes sense. If I remember correctly, if you split the line, and put resistors on each side and put the two lines back together, you subtract the two resistances. But I don't think thats correct....
Title: Re: Is there a way to subtract resistance w/out using an OP amp
Post by: GREEN FUZ on August 06, 2007, 04:23:21 PM
I`m not sure what is meant by not having an op-amp but if I understand the rest of your question correctly, yes you can reduce the resistance by putting two resistors in "parallel". There is a formula for working out the exact reduction but if, like me, you are mathematically challenged, you can go here for a handy calculator.

http://diystompboxes.com/analogalchemy/emh/emh.html (http://diystompboxes.com/analogalchemy/emh/emh.html)

or

http://www.pronine.ca/parres.htm (http://www.pronine.ca/parres.htm)
Title: Re: Is there a way to subtract resistance w/out using an OP amp
Post by: Marc.yo on August 07, 2007, 09:59:32 AM
thanks much.
Title: Re: Is there a way to subtract resistance w/out using an OP amp
Post by: CGDARK on August 07, 2007, 10:06:45 AM
Quote from: Marc.yo on August 06, 2007, 03:54:30 PM
I don't have any OP amps and I need to get a lower resistance from a resistor, if that makes sense. If I remember correctly, if you split the line, and put resistors on each side and put the two lines back together, you subtract the two resistances. But I don't think thats correct....

You can do that with resistors in parallel. Look at the section Series and parallel circuits at:
http://en.wikipedia.org/wiki/Resistor

CG