New take on "Grease Bucket" Tone

[KingOfTheRoad]

Hey All,

I have been playing around with the tone circuit in my Tele. I've done a slightly new take on Fenders "Grease Bucket" tone control. This seems to give a smooth, even sweep to the tone rather than the cut off being and the low end or high end of the rotation.

Question is ... why does it do what it does? Can the 0.02uF cap be a 0.05 with out much change. How 'bout the resistor value???

Cheers, Mike

[twangcaster1]

Not sure, man. But it'll be interesting to see what somebody who is "educated" in this matter has to say.

[ruger9]

Looks like you've got the "50's wiring" in there too (middle of vol pot to end of tone pot)

[jefrs]

What's your mod? There's a standard version?

My take on it used A250k, 100nF, 22nF and 3.9k
Caps in series like this add inversely so C = 1/(1/100 + 1/22) = 18nF
So yours is C = 1/(1/50 + 1/20) = 14nF
So changing your 20n to 50n C=1/(2/50) = 25nF
This is simplified because I have not taken the pot and resistor into account. The impedance of the rest of the circuit, including the pickups, affects the effect.

The ballast resistor stops it decending in to mud.
Rolling to the top bypasses the first cap, so 255k + 20nF (no significant effect)
Rolling to the bottom bypasses the pot, so 4.7k + 14nF (still quite bright)

The grease bucket varies the amount of capacitance as well as resistance. The capacitance gets less as the resistance is reduced. Hence a rather different roll off to the standard circuit.

Experiment with different values untill you find one you like.

[KingOfTheRoad]

Jefrs,

Hey thanks - I think your decimal points are off though. I believe that .05uF is 50,000pF and .02UF would be 20,000pF. The math is good though.

Is the any way to determine the cut off frequency?

Cheers, Mike

[Guitar_Ninja]

You're putting the tone pot in series with the volume pot. In the original configuration the volume pot and tone pot are in parallel.

In the original configuration the signal passes from the pickup selector switch through the tone pot and the volume pot simultaneously. With the modded version your signal is hitting the volume pot first, then exiting after you've set overall signal level, at which point it's affected by the tone pot.

[jefrs]

Oops, I've fixed the Farads, well spotted, nasty things pico Farads, never know when they'll sneak in. (like 220pF across the jack to dump RF).

Putting the tone control after the volume makes the volume control part of the tone control, the volume will also alter the tone. Tried it but I do find it best the other way around.

The formula for frequency is f = 1/(2piCR)
i.e. frequencies above this are transmitted to earth (caps block DC and low frequencies).
Note that should be the total resistance of the circuit. But I have not included the volume pot etc.
example
Pickup 9k Pot 250k cap 0.047 microF
pot at zero f = 376Hz
pot at 250k f= 13Hz (but little of anything is sent to earth)
As the tone pot is decreased from 250k so more and more signal of higher and higher frequencies are sent to earth. Hope that helps.

BTW my favourite tone control at the moment is the TBX which is essentially a 1Meg treble bleed to half-way then a more-or-less conventional 250k/.022mu tone control. There is a 82k in parallel with the A250k which makes it a sort of log-log pot but the A1Meg is also in play, so it's complicated.

[tdale]

Originally Posted by Guitar_Ninja

You're putting the tone pot in series with the volume pot. In the original configuration the volume pot and tone pot are in parallel.

In the original configuration the signal passes from the pickup selector switch through the tone pot and the volume pot simultaneously. With the modded version your signal is hitting the volume pot first, then exiting after you've set overall signal level, at which point it's affected by the tone pot.

If I read the schematic right, the signal will go through the 0,1 cap, even when the tone pot is turned clockwise. When the tone is rolled back, the signal goes through both caps and resistor, to ground.

I see how the circuit works, but can anyone explain what it is that makes this circuit less bassy when the volume is turned down?

Tommy