# Please School Me About Capacitors and Resistors



## BMW-KTM (Apr 7, 2015)

This is what I think I know about capacitors and resistors in a tone circuit. I could be a little bit off on some of the finer points so please correct me if I am in error.

1) When installing a cap/resistor combination to a tone pot the capacitor size is related to how far down the frequency spectrum the highs will be shunted to ground. A bigger number reaches down further so a 0.047uf reaches down more than a 0.022uf.

2) The resistor relates to the quantity of those frequencies the cap shunts to ground.

As I understand it, the cap determines the point at which the cut begins and the resistor determines the reduction slope.
I hope that's right.

*___*


The areas where I am foggy relate to the size and placement of the resistor. I have been told that a 100kΩ resistor will roughly halve the slope of the cap reduction. I don't know if that's correct or not but it's what I've been told. Two things I don't know or have never been told are:

1) The relationship between resistor value and slope. That is, if the resistor value goes up does the slope become shallower or steeper?

2) I have seen pictures of cap/resistor combinations both ways: series and parallel and I have no idea how those two ways of doing it work or what sonic differences will result.


All input is appreciated.


----------



## mhammer (Nov 30, 2007)

Capacitors store charge/current, until they can't hold any more.
Resistors block the passage of current. More resistance = less current passing through.
Reducing the current that might potentially "fill up" a capacitor, means it will take longer for that cap to fill up before it can "release" that current.
This is the basis for much of the filtering that resistor/capacitor combinations produce. There's more, but that'll get you started, as well as provide an entry point for those members who are actually schooled in electronics.


----------



## Latole (Aug 11, 2020)

IMO, signal caps use in guitar tone circuit don't store current/ voltage. They just filtering frequency


----------



## CathodeRay (Jan 12, 2018)

I'll answer just one part of this for now as well. 


) The relationship between resistor value and slope. That is, if the resistor value goes up does the slope become shallower or steeper?


Nothing that can be done in a passive single stage RC (resistor - capacitor) circuit can make the cutoff slope steeper.


----------



## CathodeRay (Jan 12, 2018)

Latole said:


> IMO, signal caps use in guitar tone circuit don't store current/ voltage. They just filtering frequency


They do. It's just the physics of the device.

The -consequence- in this case is creating a filter.


----------



## knight_yyz (Mar 14, 2015)

Adding a resistor to a pot changes the value of the pot. 
The caps filters out the high notes to ground. The higher the value the more highs will be shunt to ground when the tone knob is at zero. Therefore in this case it is a filter not a storage device
À tone knob cannot work without a cap... 

Unless you are talking about a treble bleed circuit, in which case the cap and resistor work together to keep the highs in the circuit when the volume is turned down... 


But I have never heard of using a resistor to change the slope of the cap. If you want to change the slope you change the value of the cap. Assuming you use a .047uf cap and turn the tone knob to zero, and replace that cap with a .022uf, the. 022 will have almost half the filter capacity
(.047 divided by two is. 0235 so close enough) the slope of the. 047 and therefore cut the highs half the amount of the. 047 cap at the same tone knob number. And don't forget that all caps have a tolerance of anywhere from .01 to 20 percent which also effects the amount of highs loss between two given caps with the same value. 

So in other words a .022 cap on a tone knob dialed down to zero should sound exactly the same as a. 047 cap when the tone knob is at 5 assuming both caps have identical tolerances and specifications. Which changes the slope of the tone pot.... 

Or you can change the slope by changing the pot type from linear to audio


----------



## knight_yyz (Mar 14, 2015)

here's a good article





Basic Electric Guitar Circuits 2: Potentiometers & Tone Capacitors | Amplified Parts







www.amplifiedparts.com


----------



## Paul Running (Apr 12, 2020)

It depends on what your goal is. Resistor, capacitor combinations can be configured as high, low or both (band-pass) filtering, adding an inductor to the mix, will increase the slope, depending on the Q factor of the inductor. Here's some good reading on the subject:


----------



## tomee2 (Feb 27, 2017)

A resistor has the same impedance for all frequencies.
A capacitor has an impedance that changes with frequency.
There's a frequency where the impedance of the resistor and capacitor are the same, that's where the roll off begins. If it's a tone pot, changing the resistance with the knob changes that frequency.
In a perfect world the rolloff slope is 6db per octave, no matter what the resistance.
That's my basic understanding.
Of course pickups have inductance and that changes the end result, with possible rising response that goes against what the tone circuit would do if things were perfect like on paper with equations. The rolloff slope might be different because of the pickup inductance.
Again, not an expert just my understanding of it.


----------



## BMW-KTM (Apr 7, 2015)

CathodeRay said:


> Nothing that can be done in a passive single stage RC (resistor - capacitor) circuit can make the cutoff slope steeper.


Is there anything can be done to go the other direction and make it shallower? This is actually what I am hoping can be achieved. It's kind of the main point of my OP.




knight_yyz said:


> Adding a resistor to a pot changes the value of the pot.


This part I understand. At least I think I do. A 500k resistor in parallel with a 500k pot can help a single coil to "see" a 250k pot. Do I have that correct?




knight_yyz said:


> À tone knob cannot work without a cap...


 So if a jumper was substituted for a cap the pot would not function? Or would it simply become a volume pot? Or maybe something else?



knight_yyz said:


> Unless you are talking about a treble bleed circuit, in which case the cap and resistor work together to keep the highs in the circuit when the volume is turned down.


 As I understand it a treble bleed is typically installed on a volume pot. Is that correct?




Paul Running said:


> Here's some good reading on the subject:


Thank you. A lot of that is going over my head but I am hoping if I keep with it something might click. Currently on Chapter two.


----------



## CathodeRay (Jan 12, 2018)

BMW-KTM said:


> a) Is there anything can be done to go the other direction and make it shallower? This is actually what I am hoping can be achieved. It's kind of the main point of my OP.
> 
> b) So if a jumper was substituted for a cap the pot would not function? Or would it simply become a volume pot? Or maybe something else?



a) Yes, a guitar tone control circuit is a slope adjuster - the higher the series resistance (the pot), the shallower the slope.

b) It would simply become a volume pot; the circuit becomes identical to the volume control circuit - i.e., a variable resistor to ground.


----------



## CathodeRay (Jan 12, 2018)

Part of the confusion you're going to encounter reading up on simple filters is that 99% of the info out there relates to circuits where the output is tapped -between- the resistor and capacitor so to speak.

see: https://www.daenotes.com/sites/default/files/article-images/RC-low-pass-filter-circuit.GIF

Whereas a guitar's tone circuit has the resistor in series with the capacitor to ground & the input & output are shared.

see: http://3.bp.blogspot.com/_cZpl8MVgh28/TAqfDDneKTI/AAAAAAAAAFE/ccpb7Q4ghm4/s1600/Tone+Circuit.png

Also be aware that the whole thing becomes a more complex rats nest in real life than in theory - pickup inductance and stray messiness.

As this guy JOHNH says.... "tone cap values are best picked to find your favourite sound at low tone settings, knowing that they have almost no effect at high settings"









The effect of Tone Capacitors | GuitarNutz 2


Moved, as previously posted. This post is about tone capacitors in a normal treble cut guitar tone control. Tone Capacitors This simple component can cause confusion, and expense




guitarnuts2.proboards.com


----------



## BMW-KTM (Apr 7, 2015)

The more I read about this the more I think I am on the wrong track and I need to find another way. Caps might not get me where I want to go.

Here is my situation:
I recently rewired my Partsocaster because the Kinman system I had been using failed on me (again) and I am no longer willing to keep buying more parts for it because they use shit parts and they fail with heavy use. This guitar is my #1 and it gets more use than all my other guitars put together. I originally began using the Kinman harness because I wanted the ability to swap pickups in a heartbeat and the solderless thing (they use terminal blocks now, used to be breakaway connectors) made that possible. I was also very much into the blending ability. I no longer need the solderless aspect because I have arrived at my pickup destination but I do want to retain the ability to run the neck/bridge combination. I did some reading and devised my own wiring diagram and I am happy with the result except for the neck pickup, which now seems darker than before. The bridge pup sounds like before, by itself as well as in combination with the middle but not the neck, either by itself or in combination. I want to somehow get it sounding a bit brighter. I have installed the smallest cap I have on the neck tone control (0.010uf) but now I am learning the cap does almost nothing with the tone control wide open so I'm not sure what to do. The Kinman thing sounded the way I like it but I have not been successful in replicating that.


----------



## mhammer (Nov 30, 2007)

The traditional location of a Tone control is at the input of the Volume pot. Actually, let me correct that. Some "50s" wiring puts it at the output of the Volume pot, but the vast majority of guitars made in the past 60 years stick it before the Volume pot.

While we may *think* that turning the Tone control up full removes any treble cut, there is always a teensy bit of treble lost to ground through the cap and pot. The higher the cap value, and the lower the Tone pot value, the more is lost. As tomee2 rightly noted, a cap provides a zero-resistance path to frequencies above some value determined by the cap value and several other factors.

What some do is use is a Tone pot that effectively "lifts" the connection when turned up full, such that the Tone control is out-of-circuit. I once wired up a guitar with a switch to disable the Tone pot, and the difference between a Tone pot turned up to full treble, and NO tone circuit at all, is quite audible. Such "no load" Tone pots can be purchased, although some folks simply paint a little bit of nail polish or shellac on the last little bit of the resistive strip so that when you turn the treble up full, the coating separates the pot wiper from the rest of the pot. The success of the DIY approach, of course, will depend on one's paintbrush skills but also on the construction and size of the pot. Some let you get in there and do what's needed with precision, and others not so much.

Alternatively, push-pull pots, used for Tone control, can let you disable the Tone pot. They can also let you change cap values and other components. For example, suppose you have a 500K Tone pot with the push-pull option. One position might use a .01 or even .0068uf cap that achieves a nice "rounding off" of the top end. A second position might throw a second cap in parallel (.01 + .01 = .02), as well as a 390k fixed resistor in parallel with the pot to achieve an effective Tone pot value of about 220k, such that you can now get much darker rolloffs and with less pot rotation.


----------



## BMW-KTM (Apr 7, 2015)

mhammer said:


> The traditional location of a Tone control is at the input of the Volume pot. Actually, let me correct that. Some "50s" wiring puts it at the output of the Volume pot, but the vast majority of guitars made in the past 60 years stick it before the Volume pot.
> 
> While we may *think* that turning the Tone control up full removes any treble cut, there is always a teensy bit of treble lost to ground through the cap and pot. The higher the cap value, and the lower the Tone pot value, the more is lost. As tomee2 rightly noted, a cap provides a zero-resistance path to frequencies above some value determined by the cap value and several other factors.
> 
> ...


I do have a no-load pot on hand but it's a 250k.
I will try to find a 500k no-load.
Thanks.


----------



## knight_yyz (Mar 14, 2015)

in your diagram of the circuit you posted in the other thread what is the purpose of the 500k resistor between the switch and the middle pot? Remove that and see how it sounds.


----------



## BMW-KTM (Apr 7, 2015)

knight_yyz said:


> in your diagram of the circuit you posted in the other thread what is the purpose of the 500k resistor between the switch and the middle pot? Remove that and see how it sounds.
> 
> View attachment 369902


That is for the middle single coil so that it "sees" a 250K volume pot. Actually a little more than 250 because I did not have a 500K resistor on hand so I used a 560K, which if my math is right should be about 264K. The middle pup has no tone control. It sounds fine in combination with the bridge pup. The resistor should have no influence on the neck pup when used alone. The neck pup is too dark both alone and in combination with the middle. The darkness is about equal in both cases.


----------



## BMW-KTM (Apr 7, 2015)

This is the drawing I made on my computer using elements (copy/paste) from other drawings. 

_[This post edited to add the following:]_

This diagram is incorrect. See post #20 below for the correct diagram and post #19 for the explanation why.


----------



## BMW-KTM (Apr 7, 2015)

Actually, that drawing is slightly incorrect. I made a change when I was wiring it but that change is not reflected in the drawing. It's a small and simple change and should have no affect on the circuit. I simply swapped the wires from the switch to the two tone pots such that the tone control locations mimic the relative positions of the pups. The purple bridge wire from the switch now goes to the lower pot and the neck tone is the middle pot rather than the vise-versa that is shown on the drawing. I made no other changes. The resistor is still in the same location.


----------



## BMW-KTM (Apr 7, 2015)

I revised it to reflect the actual as-built circuit.


----------



## gtrguy (Jul 6, 2006)

Have you tried disconnecting the tone control from the neck pickup? If it's still too dark with the tone control disconnected you've got something else going on unrelated to the tone control. Any chance you had the neck pickup wired in parallel previously? That would make it brighter and lower output but retain the hum cancelling.


----------



## BMW-KTM (Apr 7, 2015)

gtrguy said:


> Have you tried disconnecting the tone control from the neck pickup? If it's still too dark with the tone control disconnected you've got something else going on unrelated to the tone control. Any chance you had the neck pickup wired in parallel previously? That would make it brighter and lower output but retain the hum cancelling.


I did not change the wiring on the neck pickup. It stayed mounted in the guard. Both before and after, green/bare were used as ground and red for hot with black/white tied.


----------



## gtrguy (Jul 6, 2006)

BMW-KTM said:


> I did not change the wiring on the neck pickup. It stayed mounted in the guard. Both before and after, green/bare were used as ground and red for hot with black/white tied.


Rules out the pickup wiring then. Have you tried disconnecting the tone control to see if it still sounds dark?


----------



## Granny Gremlin (Jun 3, 2016)

tomee2 said:


> A resistor has the same impedance for all frequencies.
> A capacitor has an impedance that changes with frequency.
> There's a frequency where the impedance of the resistor and capacitor are the same, that's where the roll off begins. If it's a tone pot, changing the resistance with the knob changes that frequency.
> In a perfect world the rolloff slope is 6db per octave, no matter what the resistance.
> ...



A pot (or a resistor) can change the freq, but it can also change the depth of rolloff - depends how you use it. In a typical guitar tone circuit the pot is changing the depth, not the freq. The freq is set by the cap. That's what folks are doing when they try changing cap values, moving the point where the 6db rolloff starts. The pot then decides where the rolloff flattens out again. Tone at 0 is the pot flattening out the rolloff before it really gets going.

6db per octave is actually very little and what's called first order filtering. It is not a desired or perfect slope at all but merely the slope you get with the most basic filter (a single cap or inductor, either in series or shunted to ground). Adding a compenent to the filter (not anything anywhere but in specific ways; eg, is series cap like a basic tweeter crossover, having an inductor to ground added) increases the slope to second order 12 db per octave. Progressive orders of filter are each +6 db steeper (i.e. 3rd order is 18db per octave, 4th is 24 etc). So the simplest filter is a 6db per octave high or low pass filter that keeps going - each additional octave beyond the corner frequency continues to be -6db down. So if you have a low pass filter (treble cut) starting at 100 hz, you are down 6 db at 200Hz, 12db at 400Hz, 18db at 800Hz, 24db at 1.6kHz etc - it keeps going because the R of the cap varies with frequency (increases as F decreases) so if in series with the signal, you get a high pass (like a tweeter crossover), but is on a ground shunt (like a guitar tone control) you get a Low pass because the lows can't be shunted off to ground through the cap, so they go through to the output, but the highs can so they take the lower resistance route to ground.

Adding a resistor can also allow the slope to end - a shelving filter vs the infinate slope described above. So it's 6 db (or whatever) until a point where it flattens out and stops cuttingprogressively more - reaches max attenuation. This is true of guitar and amp (both instrument and hifi) tone controls (except amps are both boost and cut shelves, sometimes). Speaker crossovers skip the resistor (except in some higher order filters but it's doing different things there) and have an infinate slope because that is what is desired; to progressively cut off the response of that speaker component.

There are some weirder tone controls in guitars - mostly or most notably vintage Gibsons. The one on vintage EB series basses is a second order filter with infinite slope and no adjustment, just on or off. The EB3, EB2 and Ripper basses, as well as Lucile and other varitone equipped ES series guitars have an inductor (in some cases 2 in series, they all use the same part - a 30 Henry coil, so for the ES 2 in series for 60 Henries) in there and some settings are a bandpass filter (basically a high pass and a low pass in series so only some range in the middle gets through) and/or a mid scoop (same but the corner frequency of the High Pass is lower than that of the Low Pass). The LoZ (e.g. LP Recording) series, has both treble and bass, cut only, tone controls, using no inductors at all.


----------



## BMW-KTM (Apr 7, 2015)

gtrguy said:


> Rules out the pickup wiring then. Have you tried disconnecting the tone control to see if it still sounds dark?


That could probably be achieved by simply removing the cap, could it not? Seems to me that would eliminate any path to ground.


----------



## gtrguy (Jul 6, 2006)

BMW-KTM said:


> That could probably be achieved by simply removing the cap, could it not? Seems to me that would eliminate any path to ground.


Personally I'd just lift one end of the wire between the switch and the neck tone pot in case there is something wrong with that pot.


----------



## BMW-KTM (Apr 7, 2015)

I removed the tone pot from the circuit as suggested and then spent a couple of days with it. I made some adjustments to my pickup heights. I'm not sure why I had to do that since I did not remove them from the guard. Maybe the new components are a slightly different spec. Not sure. I'm going to go ahead with the 500K no-load pot idea. I think with tweaking the height screws and the tone pot being out of the loop at max I'll have a running system.

Thanks a lot for your input guys.
I appreciate it.
Rock on.


----------

