Guitar Tone Pot Wiring?

[big_teee]

Anyone ever try wiring tone Pots like this 2005 Fender Strat Highway 1 ?
Look carefully at the Tone Pots, it uses 2 Caps and a 4.7k resistor per Tone Pot!
http://support.fender.com/service_di...Bupg1_SISD.pdf
Trying to understand what does what, and if it would solve the age old problem of losing highs, when you turn down the vol. Pot?
Any thoughts?
T

[Mark Hammer]

Interesting circuit. Redrawn (very crudely), it would be essentially this (treat all periods as invisible):

From switch...

>_____/\/\/\/\/\/\/\/\/\/\/\/\/\/\_________gnd
.........|................./\..............|
.........|.................|..............|
.........|---|.1uf |------|.02uf.-|/\/\/\/\__ gnd
...............................................4k7

The 4k7 resistor sets a ceiling on how much treble cut there can be, such that there is never more than 4k7 to ground, regardless of where you have the Tone pot set.

Moving the wiper all the way to the left in our diagram, we would have 0 ohms in parallel with .1uf, so the cap provides no advantage for higher-freq content to bleed out, and is effectively out of circuit. At the same time, we would have 250k in parallel with the .02uf cap, and the cap would certainly provide a lower-impedance path for top-end to bleed to ground, relative to the 250k path.

Slide the wiper all the way over to the right, now, and we have .1uf in parallel with 250k, and .02uf in parallel with 0 ohms. here, the larger-value cap clearly provides a path for top and mids to bleed out....with the 4k7 resistor setting a limit on how severe that can be.

But what about the middle positions? Here, I would think the two caps behave like they normally would in series, and present an effective capacitance of .017uf....but with this parallel resistance.

So, the pot seems to behave in a somewhat bidirectional fashion, from all outward appearances. Surely there are those with more insight into the circuit....though I'm curious to try it out at home.

[big_teee]

Interesting circuit. Redrawn (very crudely), it would be essentially this (treat all periods as invisible):

From switch...

>_____/\/\/\/\/\/\/\/\/\/\/\/\/\/\_________gnd
.........|................./\..............|
.........|.................|..............|
.........|---|.1uf |------|.02uf.-|/\/\/\/\__ gnd
...............................................4k7

The 4k7 resistor sets a ceiling on how much treble cut there can be, such that there is never more than 4k7 to ground, regardless of where you have the Tone pot set.

Moving the wiper all the way to the left in our diagram, we would have 0 ohms in parallel with .1uf, so the cap provides no advantage for higher-freq content to bleed out, and is effectively out of circuit. At the same time, we would have 250k in parallel with the .02uf cap, and the cap would certainly provide a lower-impedance path for top-end to bleed to ground, relative to the 250k path.

Slide the wiper all the way over to the right, now, and we have .1uf in parallel with 250k, and .02uf in parallel with 0 ohms. here, the larger-value cap clearly provides a path for top and mids to bleed out....with the 4k7 resistor setting a limit on how severe that can be.

But what about the middle positions? Here, I would think the two caps behave like they normally would in series, and present an effective capacitance of .017uf....but with this parallel resistance.

So, the pot seems to behave in a somewhat bidirectional fashion, from all outward appearances. Surely there are those with more insight into the circuit....though I'm curious to try it out at home.

Thanks Mark for drawing that out.
You are showing ground in two places.
The pot is not grounded anywhere, just through the .022uf & 4k7 resistor.
I think without wiring it up, on Zero the .1uf would be full on, and the .022uf would always be in the circuit in series with the 4k7 to ground.
The only ground would always be through the 4k7 resistor?
Still a bit confused with it.
T

[Mark Hammer]

yeah, couldn't draw very well with alphanumeric characters.

The 4k7 resistors go to the pot chassis, and you can see that the pot chassis is tied to ground. So, corrected, it should be:

>_____/\/\/\/\/\/\/\/\/\/\/\/\/\/\
.........|................./\.............|
.........|.................|..............|
.........|---|.1uf |------|.02uf.-|/\/\/\/\__ gnd
...............................................4k7

There, that's better.

[big_teee]

yeah, couldn't draw very well with alphanumeric characters.

The 4k7 resistors go to the pot chassis, and you can see that the pot chassis is tied to ground. So, corrected, it should be:

>_____/\/\/\/\/\/\/\/\/\/\/\/\/\/\
.........|................./\.............|
.........|.................|..............|
.........|---|.1uf |------|.02uf.-|/\/\/\/\__ gnd
...............................................4k7

There, that's better.

The circuit must not have caught on, I've never seen it before or since.
What would happen if we did the What If?
Leave the .1uf, move the leg of the .022uf to the wiper.
Guess that wouldn't work, because you wouldn't have the 250k in the circuit?
T

[Mark Hammer]

The quirk of the circuit is that there is always 250k+4k7 tied to the input of the Volume pot, regardless of where the tonepot is set to. All that really changes is how much of that resistance is in parallel with this cap or that. So I'm guessing that the intent was to provide a tone control that provided constant loading of the volume pot in all positions.

[big_teee]

This is the way I see the original circuit, with the help of your graphics. lol

From switch...

>_____/\/\/\/\/\/\/\/\/\/\/\/\/\/\-|.02uf.-|/\/\/\/\__ gnd
.........|................./\............| 022uf..4k7___grd
................... 250k
...........|..... 1uf......|

[Mark Hammer]

Yeesh! I liked Fender's drawing better.

I'll make a proper drawing later this evening. Unfortunately, I can't post drawings from work.

[Mark Hammer]

As promised...




Weird, huh?

[big_teee]

That looks great, but that is not how I see it on the fender diagram.
the .02 is in series with the 4.7k and tied to the end of the pot, not the wiper?
The resistor and .02uf are always in the circuit, regardless how you turn the POT.
Thanks for fooling with it!
T

[Mark Hammer]

Gaaah! You're right. Man, their diagram is not very helpful!

Maybe I should just refer you to this and be done with it: Mod Garage: The Fender Greasebucket Tone Circuit - Premier Guitar

[big_teee]

Gaaah! You're right. Man, their diagram is not very helpful!

Maybe I should just refer you to this and be done with it: Mod Garage: The Fender Greasebucket Tone Circuit - Premier Guitar

You got it that time, You can see it plain on the link you provided.
Thanks, I've got to give that a try!
Thanks Mark for going the extra mile.
Terry

[David Schwab]

Anyone ever try wiring tone Pots like this 2005 Fender Strat Highway 1 ?
Look carefully at the Tone Pots, it uses 2 Caps and a 4.7k resistor per Tone Pot!
http://support.fender.com/service_di...Bupg1_SISD.pdf
Trying to understand what does what, and if it would solve the age old problem of losing highs, when you turn down the vol. Pot?
Any thoughts?
T

That's the Greasebucket tone control. It stops you from getting that bit of bass boost when you turn it all the way down. I've had customers either have me remove them, or one wanted me to put one in, and then later said he hated it, and had me remove it. Basically it removes some low end when the control is on zero to stop what Fender perceives as mud.

It has nothing to do with the volume control. You want a treble bleed circuit:

Treble Bleed Wiring Diagram