Effect of capacitor value on tone?

TelePaul

J to the R O C
Hey guys, just curious as to the impact capacitor value has on tone. Anybody care to shed some light?
 

ranjam

New member
In theory, when the control is on '10' it's effectively out of the circuit, so you can have anything there and not hear a difference. But in the real world, it may make a slight difference. But not enough to worry about, unless you like worrying about every detail.
If you are like 101% of guitar players out there, you don't use your tone control, other than checking every five minutes to make sure it is on '10'.
If you have a low value control you might get some bleed, or of you do really, honestly and truly use your tone control, bigger values bleed more treble off. Some old Strats used a .1uF and sounded like mud when you rolled off the control. They soon went to a .022uF capacitor. Gibson always used a .022uF, although some people put in a .015uF or a .01uF to not be so muddy. It's so cheap, and easy fun to experiment that you can solder away and in a day learn more than you'd imagine.
 

TelePaul

J to the R O C
Thanks alot chaps. I'd been Googling and had read some conflicting opinions. Some articles suggest that the cap only takes effect when rolling off tone, while others suggest that the fact that it exists within the circuit means that it will have some impact on tone, however negligible. This seems to corroborate what you've said Ranjam, so I'm not too bothered with making changes. It's good to know though, for sure.
 

miroslav

Cosmic Cowboy
AFA values...the beefier the cap, the more you roll off the highs.

I recently installed some DPDT mini tone toggles on a few of my guitars...and I used .015uF and .033uF for the values.
The choices worked out great (I tried a few heavier caps). The .015 j-u-s-t shaves off some of the bite on the higher strings...and the .033 give a more fatter tone with a bit more roll off.
I found a .047uF too heavy, and it just dulled the tone way too much.
A .022uF is nice...but there wasn't much difference between it and a .015 or .033...so I went the .015/.033 combination.
This is for humbuckers.
For a single coil guitar, which is usually much brighter to begin with...maybe the heavier values will work better.

With the mini toggles...I can just flip up/middle/down...and I get three distinct tones without ever touching my amp or the Tone knob on my guitar. I wired it with the middle position being neutral and no cap in line.
 

JCH

El Nacho
There is no simple answer to this question because there are many ways you can introduce the capacitor into the circuit. In a nutshell though the capacitor acts as a low pass filter. The intent is to attenuate frequencies above a certain level. There are many people who pay big money for pickups, and in reality it's the other electronics in the guitar that is making their tone suffer. For example, cheap guitar cables with high capacitance are notorious for effecting tone in a negative way. Don't focus on one component. Evaluate the whole package together.
 

Zaphod B

Raccoons-Be-Gone, Inc.
There is no simple answer to this question because there are many ways you can introduce the capacitor into the circuit. In a nutshell though the capacitor acts as a low pass filter. The intent is to attenuate frequencies above a certain level. There are many people who pay big money for pickups, and in reality it's the other electronics in the guitar that is making their tone suffer. For example, cheap guitar cables with high capacitance are notorious for effecting tone in a negative way. Don't focus on one component. Evaluate the whole package together.
No, you have it backwards. A capacitor is a high-pass filter. That's why a simple 1st-order 2-way crossover will have a capacitor in series with a tweeter - to prevent the low frequencies from reaching it. (An inductor will be in series with the woofer, to filter out high frequencies from reaching the woofer.)
 

miroslav

Cosmic Cowboy
Mmmmmmmmm....when you put a cap parallel in line with your pickup output...you roll off some highs.

So....that's a low-pass...right?
 

Zaphod B

Raccoons-Be-Gone, Inc.
Mmmmmmmmm....when you put a cap parallel in line with your pickup output...you roll off some highs.

So....that's a low-pass...right?

A cap by itself is high-pass. From what I gather, though, as wired up with a pot like in a guitar, when you put a cap in series with a resistor and if you take the output across the cap, it's a variable lowpass. :confused:

I'm gonna have to read up on it so I understand it better.
 

miroslav

Cosmic Cowboy
Yeah...I think it's how it's wired and in what type of circuit.

In the typical guitar Volume/Tone scheme...it's a low pass filter, attenuating highs relative to cap value used.
 

JCH

El Nacho
No, you have it backwards. A capacitor is a high-pass filter. That's why a simple 1st-order 2-way crossover will have a capacitor in series with a tweeter - to prevent the low frequencies from reaching it. (An inductor will be in series with the woofer, to filter out high frequencies from reaching the woofer.)

This might help
By definition, a low-pass filter is a circuit offering easy passage to low-frequency signals and difficult passage to high-frequency signals.
 

Lt. Bob

Spread the Daf!
Yeah...I think it's how it's wired and in what type of circuit.

In the typical guitar Volume/Tone scheme...it's a low pass filter, attenuating highs relative to cap value used.
A cap is definitely high-pass.
I think what's happening is that as you turn down the tone pot, you're shunting highs to ground.
The cap doesn't let the lows go to ground because it blocks them so the only freqs that get grounded out are the highs.
 

miroslav

Cosmic Cowboy
A cap alone may have a specific property, but the link JHC provided sheds light on how a capacitor can be used to create either a low-pass or high pass filter...depending on the whole circuit.

Low-pass filters

High-pass filters


As I mentioned earlier in the post...I wired a mini toggle with a couple of different value caps, and they knock off the highs....so the net result is a low pass filter controlled by the values of the capacitors used.
 

ranjam

New member
It's capacitive reactance, or Xc. Fed an AC source, any capacitor can only accumulate a limited amount of charge before the potential difference changes polarity and the charge dissipates. The higher the frequency, the less charge will accumulate and the smaller the opposition to the current. You get taught Xc = 1 / 2∏FC and you can see making 'F' bigger will make Xc smaller. What you're doing is passing the highs to ground, and the bigger the capacitor, the lower the frequency that 'everything above' goes to ground. Inductive reactance is another story; Xr = 2∏FL so the higher the frequency, the greater the resistance. Capacitors don't pass DC (the frequency is '0) and you use inductors in ∏-filter power supplies. Remember those funny Gibson ED-345's with their Varitone circuit? That added a small inductor in series with the capacitor in the tone control, so you only bled the mids (in theory) to ground. The capacitor sends only the highs, and the coil send the low part of the highs (if that makes sense), so you are supposed to end up with a notch filter.
Geez, my head feels like ginger ale now. But the real answer was guitars use a cheap treble-bleed circuit or a high-pass filter, and the highs are passed to ground. Nothing complicated.
 

miroslav

Cosmic Cowboy
But the real answer was guitars use a cheap treble-bleed circuit or a high-pass filter, and the highs are passed to ground. Nothing complicated.

You mean: a treble-bleed circuit or a low-pass filter...right? :)

If it rolls/bleeds off the highs...it's passing lows.
 

Lt. Bob

Spread the Daf!
A cap alone may have a specific property, but the link JHC provided sheds light on how a capacitor can be used to create either a low-pass or high pass filter...depending on the whole circuit.

Low-pass filters

High-pass filters


As I mentioned earlier in the post...I wired a mini toggle with a couple of different value caps, and they knock off the highs....so the net result is a low pass filter controlled by the values of the capacitors used.

yes but it's knocking off highs because it's shunting them to ground.
what's happening is that as you turn down the tone pot, you're shunting highs to ground.
The cap doesn't let the lows go to ground because it blocks them so the only freqs that get grounded out are the highs.



. But the real answer was guitars use a cheap treble-bleed circuit or a high-pass filter, and the highs are passed to ground. Nothing complicated.
 

miroslav

Cosmic Cowboy
Fine...but the net result is a low-pass filter. :)

I just don't see how that circuit can be called a high-pass filter if the highs are being rolled off...? ;)
 

Lt. Bob

Spread the Daf!
because it's only passing highs to ground where they effectively disappear. If it were a low-pass ..... then it would make things more trebly because it would pass lows to ground making them effectively disappear.

The net result is certainly that it gets less highs going to the amp ..... but that's because the high-pass of the cap let's those highs go to ground rather than the amp.
I suppose it could be argued that from the amplifiers POV the guitar becomes a low-pass but that is because the cap part of that circuit is a high pass filter grounding out progressively more highs as you turn down the tone.
 

miroslav

Cosmic Cowboy
Well...I'm looking at the net result, and using that to name the filter, rather than looking just at the cap and how it would behave sans grounding of the highs.

That complete circuit in the guitar has the net effect of removing highs...so to me it will always be a low-pass filter.
It just makes no sense to call it a high "pass" when in fact it's NOT passing highs at the output...where we hear it...where it matters to us. :)
 

mshilarious

Banned
A capacitor is a device which has decreasing impedance with frequency. Thus, a series capacitor forms a high-pass filter together with the load impedance (passive guitars usually don't have series capacitors); a parallel capacitor forms a low-pass filter together with the source impedance of the pickups as higher frequencies are shunted to ground. The corner frequency of the filter is dependent upon the capacitance as well as the other impedances in the circuit; this will generally not change as the tone pot is changed, but may change according to other settings on the guitar.

In the case of a guitar, a pickup is an inductive source, so a resonant filter is formed, also known as a tuned circuit or LC circuit. This means that there will be a boost at some frequency, typically somewhere in the midrange for usual guitar combinations. Given the resistance from the volume and tone pots, this will usually only be experienced at full-on volume and full-off tone, and it is also limited by the damping effect of the pickup's resistance.

When the tone is not full on or off, we have a shelving high-cut filter. That is, the resistance of the pot acts as a limit on the HF loss--at frequencies where the capacitor is effectively zero impedance, the signal loss can be defined as a voltage divider between the source impedance and the tone pot impedance. Note that since the pickup is inductive source, if the frequency gets high enough we'd see a first-order filter, 6dB/octave drop.

In contrast, at tone full-off, we have up to a second-order high-cut (low pass) filter, where the signal loss will increase at 12dB/octave above the corner frequency (which is the -3dB point). Due to the resistances involved, typically we would have somewhere between 6dB and 12dB/octave loss at frequencies of interest.

The corner frequency, as noted above, is dependent upon the source impedance of the circuit. That can change with pickup selection and volume pot setting. Figure your neck and bridge humbuckers might be something like 8K and 11K nominal, that's not a huge difference, but a 500K volume pot set at mid-resistance (250K from wiper to each leg, this is *not* the midpoint on an audio taper pot) will have ~125K output impedance.

This becomes important where the tone pot is wired after the volume pot, which can make your tone pot darker when volume is not full up (or rather low). Some wirings have the tone pots before the volume pots, some have them after. I think typically Strats are before and LPs after. Note that if you rewire your volume pots to the "independent" configuration, you need to pay attention to the resulting effect on the tone pots, if you care.

On the other hand, in the middle pickup setting both pickups are in parallel, so their source impedance drops and corner frequency will go up very roughly by two (with volume pots full up of course, if the tone pots are after). The same effect will be created by a coil tap.

So as you can see, tone controls can be kinda crazy devices . . . I don't use them on guitar, but I use them quite a lot on bass.
 
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