Tone Pot Question

[au_rick]

Hi All,
can someone please help me understand the tone pot ?
Leaving aside the capacitor value;
Single coils generally use 250k, humbuckers and P90's use 500K, because a higher value gives a brighter sound, right ?
BUT, both have zero resistance when wound to 10, so how does one make a pickup sound brigter than the other (being at full brightness on 10) ?
Further, if a 500k pot is would half way (ie. to 250K) what is the difference ?

 

[Wilko]

Much more subtle difference in the tone spot, but it raises the cutoff frequency so you're rolling off less highs, so it sounds brighter overall when using the tone control

 

[c_wester]

"both have zero resistance when wound to 10"

Its the other way around.

 

[PaulD]

The tone pot on a guitar is wired as a variable resistor, when the pot is on 10 the resistance will be equal to the pot value and the high resistance will prevent virtually any of the high frequencies from being bled off to ground through the capacitor (the capacitor value determines the roll off frequency). As the pot is turned down the resistance decreases allowing progressively more of the higher frequencies to be bled off, when the pot is on 0 there is no resistance and all of the high frequencies will be bled off.

Tone pots are usually log taper pots so a 500k pot at half way will be 50K, not 250K. 250K would occur at 9 on the pot scale.

 

[au_rick]

The tone pot on a guitar is wired as a variable resistor, when the pot is on 10 the resistance will be equal to the pot value and the high resistance will prevent virtually any of the high frequencies from being bled off to ground through the capacitor (the capacitor value determines the roll off frequency). As the pot is turned down the resistance decreases allowing progressively more of the higher frequencies to be bled off, when the pot is on 0 there is no resistance and all of the high frequencies will be bled off.

Tone pots are usually log taper pots so a 500k pot at half way will be 50K, not 250K. 250K would occur at 9 on the pot scale.

Thank you, so basically the pot controls how much impact the capacitor has on the tone, and the cap value determines which frequencies are bled to ground ? ?

 

[DrewB]

The tone pot on a guitar is wired as a variable resistor, when the pot is on 10 the resistance will be equal to the pot value and the high resistance will prevent virtually any of the high frequencies from being bled off to ground through the capacitor (the capacitor value determines the roll off frequency). As the pot is turned down the resistance decreases allowing progressively more of the higher frequencies to be bled off, when the pot is on 0 there is no resistance and all of the high frequencies will be bled off.

Tone pots are usually log taper pots so a 500k pot at half way will be 50K, not 250K. 250K would occur at 9 on the pot scale.

Great explanation as to what's happening!

 

[guitplayer]

For a more woody sound, try having no tone pot.
Wired straight to the VOL

 

[PaulD]

Thank you, so basically the pot controls how much impact the capacitor has on the tone, and the cap value determines which frequencies are bled to ground ? ?

Yes, exactly

 

[au_rick]

Yes, exactly

Thanks again.
Soooo,
is there any tonal difference between having the cap wired between the volume and tone pot and having the cap connected to a lug on the tone pot and then grounded to the tone pot (ie, plain wire between the volume and tone pots) ? I'm guessing that the physical difference is that it changes the location of the cap relative to the resistor, but being as it is the path to ground either way, does this actually make a difference ?)

 

[Jethro Rocker]

The tone pot on a guitar is wired as a variable resistor, when the pot is on 10 the resistance will be equal to the pot value and the high resistance will prevent virtually any of the high frequencies from being bled off to ground through the capacitor (the capacitor value determines the roll off frequency). As the pot is turned down the resistance decreases allowing progressively more of the higher frequencies to be bled off, when the pot is on 0 there is no resistance and all of the high frequencies will be bled off.

Tone pots are usually log taper pots so a 500k pot at half way will be 50K, not 250K. 250K would occur at 9 on the pot scale.

Very good explanation. As the cap is merely determining the frequency bleeding to ground, the material of said cap should have zero impact on the tone of the signal as output signal does not pass through the cap.

 

[PaulD]

Thanks again.
Soooo,
is there any tonal difference between having the cap wired between the volume and tone pot and having the cap connected to a lug on the tone pot and then grounded to the tone pot (ie, plain wire between the volume and tone pots) ? I'm guessing that the physical difference is that it changes the location of the cap relative to the resistor, but being as it is the path to ground either way, does this actually make a difference ?)

No, it makes no difference. Think of the tone control circuit as a spur off the signal path that consists of a variable resistor and a capacitor in series connected to ground, the variable resistor (pot) acts like a valve that controls how much signal flows along that path, it doesn't matter which way round they are, the effect is exactly the same.

The point at which that spur connects to the signal path can have an effect however, this is is the difference between 50's and modern wiring. With modern wiring it connects to the input side of the volume control and with 50's wiring it connects to the output side.

 

[guitarvoodoo]

Guys, 2 follow-up questions:
1. What effect does a higher cap value have on the frequency roll off point?
Does a higher cap value increase the frequency or lower it?
2. How much impact does the max value of the pot have on the amount of high fequency signal lost to bleed when the tone pot is at 10?
In other words, does it make much difference if it's say, 400K, or 500K, or 600K Ohms? Or 250K for that matter.

(Edit: Wow, just saw that this is my 2000th post!)

 

[poor man's burst]

Guys, 2 follow-up questions:
1. What effect does a higher cap value have on the frequency roll off point?
Does a higher cap value increase the frequency or lower it?
2. How much impact does the max value of the pot have on the amount of high fequency signal lost to bleed when the tone pot is at 10?
In other words, does it make much difference if it's say, 400K, or 500K, or 600K Ohms? Or 250K for that matter.

(Edit: Wow, just saw that this is my 2000th post!)

The higher the value (22nF being higher than 15nF), the lower the frequency.
The pot value at 10 has an impact. However, its amount is subjective. The best way to make yourself an idea is to try a Fender Esquire and compare the switch middle position (pickup with volume and tone control) and the 3rd position (pickup with volume control only, equivalent to tone pot of infinite value).