Resistor values

[SprinkleSpraycan]

I want to finish a build but am short a 27r resistor. Is there a way to stack a larger size with a capacitor to come up with the same value?

[MikeA]

You can put two or more resistors in series, in which case their sum is the total resistance (16 + 11 = 27 for example.) Or you can put two or more in parallel, in which case the sum of their reciprocals is the reciprocal of the total resistance (62 and 47 in parallel are 26.7, which is close enough, for example.)   This calculator will let you put in your target  resistance (27 ohms) and will give you several combinations of larger resistors in parallel that will give you that.   http://www.sengpielaudio.com/calculator-parallel.htm

[SprinkleSpraycan]

Rad. Thanks. I knew about adding in series but I didn't know I could go smaller with parallel.

[antonis]

Is there a way to stack a larger size with a capacitor to come up with the same value?

Of course you can but for a specific frequency only...

Just wire the capacitor across the resistor..
(in parallel, like MikeA told you..)

[SprinkleSpraycan]

Is there a way to stack a larger size with a capacitor to come up with the same value?

Of course you can but for a specific frequency only...

Just wire the capacitor across the resistor..
(in parallel, like MikeA told you..)

So if I'm trying to reach 27r, how to I calculate which resistor and capacitor to combine? Will a capacitor create a lag time? I doubt I would hear it but I'm curious.

[GibsonGM]

If it is a cap and R in parallel, if you add 2 R's to get the value and bridge them with the cap, the response of the network will be identical to the original design.

If you post a pic of exactly what you're doing, we could give you a lot more precise info 

[antonis]

So if I'm trying to reach 27r, how to I calculate which resistor and capacitor to combine?

It depends on resistor values availiability..
For resistors of value bigger than 27R, you'll have to wire the capacitor in parallel where for resistors of value smaller that 27R you'll have to wire the cap in series..

Capacitors exhibit a "resistance" (Xc) calculated via Xc = 1/2πfC, where f = frequency of interest and π = 3.14..

33R // 3.3nF (at 318Hz) -> 27R

22R + 100μF (at 318Hz) -> 27R

[PRR]

WHY are we talking capacitors at ALL???

This misses the problem of "smaller resistor".

> Capacitors exhibit a "resistance" (Xc) calculated via Xc = 1/2πfC

And since "audio" covers 100:1 of frequency, this is not useful for a "resistance" problem.

[antonis]

WHY are we talking capacitors at ALL???

Because that was OP's itch..

>Is there a way to stack a larger size with a capacitor to come up with the same value?<

[pacealot]

And we still don't know what fragment of what sort of circuit this resistance and/or capacitance value is applicable to.... 

[GibsonGM]

If it is a cap and R in parallel, if you add 2 R's to get the value and bridge them with the cap, the response of the network will be identical to the original design.

If you post a pic of exactly what you're doing, we could give you a lot more precise info 

[bluebunny]

Forget "capacitor".  Folks are going off on a tangent because you unwittingly mentioned capacitor in your opening post.  Mike's first reply is what you need.

[antonis]

Forget "capacitor".  Folks are going off on a tangent because you unwittingly mentioned capacitor in your opening post.  Mike's first reply is what you need.

 

[bluebunny]

We still love you, Antonis!   

[pacealot]

(and also, perhaps the 27Ω value isn't hyper-critical and you could sub in something that's close that you already have, but we don't know because we haven't seen what circuit this applies to...)

[bluebunny]

^^ This is also a good point.  I'm guessing a value that low is part of some basic power filtering?  In which case a piece of wire would suffice for the time being.  Or any other low-value resistor you have to hand (<100R).  Show us the schematic and we'll know for sure.

[SprinkleSpraycan]

Wow! Such enthusiasm. It's for an OCD clone. The adhd from pedalpcb. It is the first resistor after the diode at the incoming 9v. I used a 51r in parallel with 47r as those where the values I had in hand that was closer to the calculator. Pedal sounds great and thanks to everyone. I said capacitor not knowing I could use resistors in parallel. I've only been doing this since November so every project is a new learning experience.

[SprinkleSpraycan]

Looks good too. I went a more aggressive direction than the fulltone art.

[bluebunny]

It is the first resistor after the diode at the incoming 9v.

Yep, part of the power conditioning.  Your solution fits the bill (the value isn't critical).  Good that you've got it all working to your liking.  Nice build. 

[antonis]

Your solution fits the bill (the value isn't critical).

I suppose OP would like to know WHY particular resistor value isn't critical..
(after all, he declared that: "every project is a new learning experience."..)



So Marc, could you plz give us some info about power supply LPF (R20/C11) and Vcc voltage (compared to (+)) regarding circuit's current consumption..??