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

[Top-L]

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.

I just caught this. What is the exact effect of the tone pot increasing the ohm value of the volume?

For instance, when I swapped the original 500K vol for a 250K vol. It sounded close to what I'm used to, but imo was a bit darker. I wouildn't be surprised to find out that a 250K volume is the exact same as a 500+500 volume/tone, and that the difference I heard came down to tolerance of parts.

If anyone knows, would a 250K vol be expected to be darker than a 500+500? And what is the theoretical identical volume pot to 500+500t?

In the past I have just swapped parts on recommendation, now I'm trying to learn what is actually happening.

 

[freefrog]

If anyone knows, would a 250K vol be expected to be darker than a 500+500? And what is the theoretical identical volume pot to 500+500t?

A 250k vol. alone creates exactly the same resistive load than a 500k volume in parallel with a 500k tone.

And it's somehow brighter than a 500k volume when lowered: when a pot is set exactly at half of its resistive value, it puts 50% of its resistance between pickup and output + the other 50% between output and ground. In this case, a 250k pot puts only 125k between pickup and output while the 500k doubles this value and trims the high range accordingly.

As I said before, it doesn't make indifferent the presence or absence of tone caps. Many experiments have been done about that here and show how harmonics change when a capacitor is there VS when the load is only resistive.

As a footnote, I share a (voluntarily trimmed) comparison involving the electrically induced resonant peak of a pickup with 500k and 250k volume pots, full up then lowered. The curves have been aligned automatically by the lab gear used but the difference remains perceptible and should allow to "get the picture"...



FWIW. HTH.

 

[Top-L]

Very cool.

When I swapped the 500K for a 250K volume, I wasn't using a capacitor on the volume pot (because the original 500K didn't come with one). From what I've read, a volume pot capacitor allows an extra amount of high frequency content through. This might explain why I perceived the 250K alone as being slightly darker and less airy. Or it could just be variation in parts.

Now the guitar has been rewired with a 500K push pull (sans cap), and temporary 500K tone pot while I wait for resistors. AFAICT, the volume and tone are parallel, so if I replace the 500K tone with a 1M resistor, the effective load would be 750K.

It seems to me that there are several options to customize the tone of the circuit, just using different parts.

* 250K vs 500K (or other) pots. Higher resitance will pass more signal in the 1- 2.5K ish range.
* Adjust the tone pot capacitor. (Will bleed some extra HF content, unknown where in frequency.)
* Add/adjust vol pot capacitor. (Will bleed some extra HF content when turning down, but also some when on full.)

 

[beaubrummels]

To clarify: a cap in parallel on the volume is a form of treble bleed, which is different from a cap in series to ground on a tone. They are wired differently.

 

[freefrog]

Very cool.

When I swapped the 500K for a 250K volume, I wasn't using a capacitor on the volume pot (because the original 500K didn't come with one). From what I've read, a volume pot capacitor allows an extra amount of high frequency content through. This might explain why I perceived the 250K alone as being slightly darker and less airy. Or it could just be variation in parts.

Now the guitar has been rewired with a 500K push pull (sans cap), and temporary 500K tone pot while I wait for resistors. AFAICT, the volume and tone are parallel, so if I replace the 500K tone with a 1M resistor, the effective load would be 750K.

It seems to me that there are several options to customize the tone of the circuit, just using different parts.

* 250K vs 500K (or other) pots. Higher resitance will pass more signal in the 1- 2.5K ish range.
* Adjust the tone pot capacitor. (Will bleed some extra HF content, unknown where in frequency.)
* Add/adjust vol pot capacitor. (Will bleed some extra HF content when turning down, but also some when on full.)

*Yep, a volume with "treble bleed" makes the sound brigher, just like a bright cap on the volume pot of a Fender amp.

*FWIW, 500k vol and 1M tone in parallel = a resistive load of 333.3k. There's a bunch of online calculators to do the maths if needed. Example: https://www.digikey.com/en/resource...rsion-calculator-parallel-and-series-resistor

*The tone of a circuit can absolutely be "tuned" by using different resistive and capacitive loads. And all is predictible once understood.


Side note... Beau', a tone cap is in "series" between pot and ground but the whole pot + tone cap is still in parallel with the pickup(s). And if a treble bleed cap is effectively in parallel with a variable resistance depending on the taper of the volume pot, this treble bleed cap stays largely in series with the signal path, just like a coupling cap in a pedal or amp.
I don't write that to argue or to deny your statement: I just underline in a friendly way that the ideas of "parallel" or "series" components can change according to the perspective.

 

[beaubrummels]

Side note... Beau', a tone cap is in "series" between pot and ground but the whole pot + tone cap is still in parallel with the pickup(s). And if a treble bleed cap is effectively in parallel with a variable resistance depending on the taper of the volume pot, this treble bleed cap stays largely in series with the signal path, just like a coupling cap in a pedal or amp.
I don't write that to argue or to deny your statement: I just underline in a friendly way that the ideas of "parallel" or "series" components can change according to the perspective.

The point was simply how they are physically wired, cap relative to pot. That's all. Sounded like Top-L was about to put a tone cap on the volume. Getting too pedantic just makes it more confusing.

 

[freefrog]

Back on topic. Let's share below the copy of an online pic meant to show a "basic electric guitar circuit" and that I've modified / completed in a few seconds. It will illustrate what I was trying to share in my previous post AND it might clarify the question discussed in this thread: the bottom pic swaps the tone pot for a resistor, showing how it can be wired in order to emulate a tone control set @ a fixed value.

Not that a tone pot is always wired like in the upper pic, for sure... but maybe this stylized representation will help a bit, who knows?



FWIW, as usual.

 

[Top-L]

While we're on the subject... resistor kit should be here tomorrow.

This guitar does not have a tone knob, so I will just use resistors and test values between 500K and 1000K. Hopefully I will find my preference. Am I correct in assuming that a change to the total circuts resistance, from say 250K to 300K, is going to have a much greater effect than the treble bleed from the volume capacitor? So if I am experimenting with alternate tone controls, does the treble bleed on volume even matter?

 

[beaubrummels]

They all have an effect. The effects are slightly different. Treble bleed effect isn't as obvious until you roll the volume down. Your fixed tone control will be in effect all the time, however.

 

[freefrog]

While we're on the subject... resistor kit should be here tomorrow.

This guitar does not have a tone knob, so I will just use resistors and test values between 500K and 1000K. Hopefully I will find my preference. Am I correct in assuming that a change to the total circuts resistance, from say 250K to 300K, is going to have a much greater effect than the treble bleed from the volume capacitor? So if I am experimenting with alternate tone controls, does the treble bleed on volume even matter?

Question answered above.

You've said that your volume pot had no treble bleed cap anyway... but if ever you decide to add one, experimenting with different treble bleed cap values might give you noticeably different results once the volume control lowered. It's also possible to add resistors in "series" or in "parallel" with the treble bleed cap, in order to fine tune the result: google about "Duncan" or "Kinman" treble bleeds if ever you're interested.

As in my previous posts, sharing these precisions is meant to reply to the last sentence of your post 21. HTH. ;-)

And let us know which resistive load you prefer... Good luck in your experiments!

 

[Top-L]

I finished this guitar. A 331 treble bleed cap makes a noticeable, positive improvement when volume rolled down. Never ab tested this before, but this is mandatory. Now i have to put one in several guitars.

I used a 470k + 100k in series with 223 cap to simulate tone control. It sounds about right.

 

[marcello252]

I used a 470k + 100k in series with 223 cap to simulate tone control. It sounds about right.

that's a 570K pot , I don't think it's noticeable but it would be a strange pot

 

[beaubrummels]

that's a 570K pot , I don't think it's noticeable but it would be a strange pot

FYI pots that are 20% tolerance can be as high as 600k. It's within normal range for that kind of pot.

 

[Top-L]

FYI pots that are 20% tolerance can be as high as 600k. It's within normal range for that kind of pot.

Thats what I was going for, a "bright" 500K.

 

[marcello252]

FYI pots that are 20% tolerance can be as high as 600k. It's within normal range for that kind of pot.

I know, my first post in this thread was about the big tolerance in pot

 

[beaubrummels]

I know, my first post in this thread was about the big tolerance in pot

Yeah, I get that, but in the last post you said it was strange. I was just pointing out that it's actually normal. I've bought pots in bulk or even small bunches before and tested each one individually and there's always quite a distribution of high and low pots out to the limits of the tolerance.