Is there a resistor that will simulate an open tone control?

[Top-L]

Last year I received a single volume knob guitar with a 500K pot. After several pickup swaps I figured out that the lack of tone pot made the guitar seem too bright.

I found that by swapping the vol with a 250K pot, that the sound was much closer to a typical 500K+500K setup.

However, the guitar is a little bit dark. The switch needs replace, and while I'm in there I am going back to a 500K volume. I will either wire in a 500K tone pot and tuck it away in the cavity, or ideally there is a resistor that will have the same affect.

Anyone know what that resistor would be?

 

[beaubrummels]

I would use alligator clips to put a tone pot temporarily in there, turn it to where you like it, then measure the resistance of the pot, and just buy a resistor of that value, if you want it to be static and permanently set. But for a tone, you still need a cap and a resistor combination. A resistor to ground by itself is mostly going to lower the output, though it may take some of the top end off with it.

 

[Top-L]

I would use alligator clips to put a tone pot temporarily in there, turn it to where you like it, then measure the resistance of the pot, and just buy a resistor of that value, if you want it to be static and permanently set. But for a tone, you still need a cap and a resistor combination. A resistor to ground by itself is mostly going to lower the output, though it may take some of the top end off with it.

So basically if I like the sound with the 500K pot fully open, that would be "off" and 500K resistance?

 

[beaubrummels]

So basically if I like the sound with the 500K pot fully open, that would be "off" and 500K resistance?

Well, you'd want a little less resistance for it to behave like a pot that is leaking a little off the top, but you also need the normal cap for that type of guitar. For example, to simulate a humbucker-equipped tone control on 10, I'd have about 495k ohm resistance and the normal 0.022uF cap to ground tapped off the volume lug. You might have to put resistors in series to get the value you want. Something like this:

volume hot lug > 330k > 150k > 15k > 0.022uF > ground.

But you'll have to play with it in your guitar to figure out what values work best. Try it with and without the cap and see what the difference is.

 

[Clint 55]

I'd just pick whatever resistor you have that is marginally below 500k. 500k pots aren't all exactly 500k.. And yes, use the cap too if you want it to sound like a tone full up.

 

[ehdwuld]

Think treble bleed with series cap and resistor

If a 500k is too bright and a 250 is too dark

Put a 500k linear in as the pot
Then alligator clip a 500k resistor in Parallel with the ground and hot
this will make the make the pickup see a 250k
pot ( messes with thae taper of the pot)
Use a linear pot so it makes it look like an audio taper

Increase the value of the resistor and more goes thru the real pot
increasing the value of what the pot sees

Use clips until you find the value you like then solder in a permanent resistor
you amy want a 300 k or 450k pot

If that is the case then you can swap in that value pot

Alternatively

You can put a 250k linear pot in
And put a 250 k resistor in series with the signal

This will make it where your volume doesnt actually turn off
But behave like an audio taper
Where halfway is the effective as off

But the pickup sees 500k -250k

 

[Spaghetti Bolo]

If 500k is too bright and 250k too dark then just use a 500k pot and parallel it with a resistor above 500k. 1 Meg is a common value and will effectively give you a roughly 330k load.

 

[beaubrummels]

Another option is just use a 330k pot for single volume, or get a few 500k volume pots and measure to find the one that is the lowest in tolerance and just use that.

 

[ehdwuld]

I see where i wrote that wrong

Its correct now

What Clint said

 

[Top-L]

This is the final frontier. All these years swapping pickups and all i want is the exact right amount of air on top.

 

[grumptruck]

I would start with a 330k volume pot and if that doesn't work... try to find the sweet spot with a 500k post and resistors.

 

[freefrog]

This is the final frontier. All these years swapping pickups and all i want is the exact right amount of air on top.

FWIW, I use sometimes mini trim pots for that. A 470k trim pot in series with a 220k resistor would give an array of values between 220k and 690k for a "fixed tone control", allowing probably to find the desired sweet spot.

Nothing else to add to the excellent advices given by our fellow members, except a confirmation on a detail: a tone pot full up is mostly a resistive load and matters therefore for its resistance mainly. The effect of its capacitor on fundamental notes can't be really heard before 3.5/10 approximatively in most cases. That said, tones caps can have a slight effect on harmonics even when a tone pot is full up. Reason why I personally like to add a tone cap in series with a resistor (and/or trim pot) emulating a tone control when I do such things. It's not expensive nor cumbersome or difficult to add.

HTH. Good luck in your tinkering.

 

[Top-L]

FWIW, I use sometimes mini trim pots for that. A 470k trim pot in series with a 220k resistor would give an array of values between 220k and 690k for a "fixed tone control", allowing probably to find the desired sweet spot.

Nothing else to add to the excellent advices given by our fellow members, except a confirmation on a detail: a tone pot full up is mostly a resistive load and matters therefore for its resistance mainly. The effect of its capacitor on fundamental notes can't be really heard before 3.5/10 approximatively in most cases. That said, tones caps can have a slight effect on harmonics even when a tone pot is full up. Reason why I personally like to add a tone cap in series with a resistor (and/or trim pot) emulating a tone control when I do such things. It's not expensive nor cumbersome or difficult to add.

HTH. Good luck in your tinkering.

Just so im clear, a 500k tone pot that is fully open is just providing roughly 500k resistance to those lugs and nothing else? When you back off the tone, the resistance decreases, and more of the signal is run through the tone pot cap, which determines what frequencies are attenuated?

Or is it that some signal always going through tone pot, even when fully up?

Iow, if i use the mini trim pot and resistor, will i also need the small cap?

This is a more elegant solution. I always have tone pot fully open, but for some reason when not connected, guitar is too bright, even if by a little. Its hard to explain, but it sounds very mildly grating without the tone pot.

And also just so im clear, a 250k tone pot would sound like a 500k liner pot on half?

 

[Spaghetti Bolo]

Just so im clear, a 500k tone pot that is fully open is just providing roughly 500k resistance to those lugs and nothing else? When you back off the tone, the resistance decreases, and more of the signal is run through the tone pot cap, which determines what frequencies are attenuated?

Something like that.

Or is it that some signal always going through tone pot, even when fully up?

Something like that. The pickup, passive controls, cable and input stage of whatever you're plugged into combine into a filter network with a resonant peak.

Iow, if i use the mini trim pot and resistor, will i also need the small cap?

It won't hurt but I don't think anyone could hear in this application in a blind test (I know I can't).

This is a more elegant solution. I always have tone pot fully open, but for some reason when not connected, guitar is too bright, even if by a little. Its hard to explain, but it sounds very mildly grating without the tone pot.

That's because the tone pot is providing an additional load to the pickup. Disconnecting it is the functionally the same as increasing the ohm value of the volume control.

And also just so im clear, a 250k tone pot would sound like a 500k liner pot on half?

That's it exactly. On the other hand, turning down a 500k volume control does not sound like a 250k on 10.


I'm guessing this guitar has everything mounted on a scratchplate? Which is a huge PITA when it comes to this kind of fine tuning. Even so here's what I would suggest; Replace the current volume control with a 500k linear. Connect hot to the center lug, and lug 3 to ground. You now have a variable load. At 10 it will represent a 500k volume on 10. Turning the control down to 0 will ground the signal. 5 will simulate a 250k pot on 10.

Turn that around whilst playing through your rig and see if you find the sweet spot you're seeking.

This way you will hear and experience the tonal difference first hand.

 

[Clint 55]

No, a 500k tone pot full up does not only provide 500k of resistance until you turn it down. The signal always passes through 500k (or whatever you turn it down to) of resistance and the cap. So to simulate a 500k pot full up you bridge a resistor in that range then a cap between the signal and ground.

 

[freefrog]

Just so im clear, a 500k tone pot that is fully open is just providing roughly 500k resistance to those lugs and nothing else? When you back off the tone, the resistance decreases, and more of the signal is run through the tone pot cap, which determines what frequencies are attenuated?

Or is it that some signal always going through tone pot, even when fully up?

Iow, if i use the mini trim pot and resistor, will i also need the small cap?

This is a more elegant solution. I always have tone pot fully open, but for some reason when not connected, guitar is too bright, even if by a little. Its hard to explain, but it sounds very mildly grating without the tone pot.

And also just so im clear, a 250k tone pot would sound like a 500k liner pot on half?

What Spaghetti Bolo said for the most part and I thank him to have aleviated my task to some extent. My experience and his differ on the detail evoked below .

It won't hurt but I don't think anyone could hear in this application in a blind test (I know I can't).

In my experience, people may hear it or not according to the gear/settings involved and to their ears/needs.

With a 500k resistor simulating a tone pot, the absence or presence of a regular 47nF tone cap between resistor and ground makes a measurable difference of 2.18dB in the resonant peak of a Fender style single coil, for instance. IOW, the pickup is 2.18dB brighter without cap than with it.

I've faced this again recently with a Telecaster including a no-load tone pot: it was perfect for the neck PU but the bridge one + a crude resistor was still too bright. When I lowered the value of the resistor, the tone was just thinner. I've added a tone cap in series with the resistor and all was right : fundamental notes had their full strenght and upper harmonics were less agressive. Very obvious through an amp played loud in this case.

Now, I fully agree with the advice saying that people must test that by themselves: nothing is worth direct personal experience here. And alligator clips make it easy...

 

[marcello252]

A good pot has a 10% tollerance, a not so good pot even more, so it can go from 450 to 550 and still being on specs, take a normal 470K R, a 22nF in series and put the couple in parallel with the input lug of the volume for a conventional setup or the central lug for the 50s type wiring, you can't go wrong

 

[Top-L]

I wired up this guitar with a 500K tone pot just to make sure its working. Also because I don't have any loose resitors lying around. Feels funny buying $10 in resistors, when I have tons of free pots in my box. But it also feels funny having a loose tone control tucked in the cavity.

 

[ehdwuld]

I wired up this guitar with a 500K tone pot just to make sure its working. Also because I don't have any loose resitors lying around. Feels funny buying $10 in resistors, when I have tons of free pots in my box. But it also feels funny having a loose tone control tucked in the cavity.

Hmmm
thats a common choice
Between too cheap and good sense

 

[Top-L]

Eh. I'll swap the pot for resistors when I find some worth ordering. I haven't had time to shop amazon. There is probably a kit that includes different values. I was also contemplating a mini trim pot.