potentiometers question

[James Davidson]

so im going to put a hot rails in the middle position of my stratocaster but i heard that you should change the volume pot to from 250k to a 500k.

the thing is, that will affect the sound of the other single coil i have in the neck position will it not? i dont have tone controls so i dont need to change them and i dont have a bridge pickup.

is there any solution to this problem?

 

[Gypsyblue]

Re: potentiometers question

That's a pretty bizarre set-up. No bridge pickup you say? Well, I think I'd just connect the Hot Rails to the selector switch, as usual, and use a single 250K master volume pot as Seymour (and Leo Fender) intended.

But if you really want to add a 500K pot you could. Sounds like you have room for it.

I wouldn't do this but you might want to give it a try: connect the neck pickup first to the 250K volume pot and the output of that volume pot to the selector switch. Then connect the Hot Rails to the 500K pot and the output of the 500K pot to the selector switch. The output of the selector switch would go to the output jack as usual.

 

[Farkus]

Re: potentiometers question

Well, it really depends on what you like.

In general, if you switch to 500K pots the neck single coil will be brighter. That said, if you stick to the 250k pot the hot rail might be too dark. I personally dislike a true single coil (most of them, especially vintage voiced) with a 500k pot. Give it a try with the 250K and if the hot rail sounds way too muddy with it get the 500K volume pot.

 

[GuitarDoc]

Re: potentiometers question

Or, if you only want the one vol control, use the 250k pot and add a 250k resistor in series with the hot rails pup.

 

[RayBarbeeMusic]

Re: potentiometers question

Or, if you only want the one vol control, use the 250k pot and add a 250k resistor in series with the hot rails pup.

Exactly wrong. You don't want a 250k resistor in series with your pickup, it will darken the pickup up like having a 500k pot rolled half way down.

When you use a volume pot wired normally, your pickup is on one side of the resistance, ground on the other side, and a wiper that moves between the two is your output. When you roll the pot down, you are introducing a series resistance between your pickup and the output, which is one reason your pickups get dark when the volume is rolled down unless you have some sort of cap or RC network between the hot input and the wiper.

That is also why amps have "bright caps" on the volume, to compensate for that. Except the guys who designed those never ever bothered to actually calculate out a RC network that would keep the same tone at different volume levels, which is why most amps with bright caps sound obnoxious and thin at lower volumes.

It's also why, for those of us who design tube amp circuits, we put a series resistance in the circuit. It is a signal level control, though it doesn't work nearly as well as a voltage divider, but it is also a TONE SHAPING control.

Point: Series resistance between guitar pickup and switch = foolish.

What you can do, and I've done it many times, is have a 500k pot and for the pickups you want to see 250k, put in a 500k (you're more likely to find 470k, but close enough, or you can go larger to) resistor from that switch position to ground. That puts the resistor in PARALLEL with the pot, not in series.

The only downside there is that when those 2 pickups are in parallel, both see the 250k, but if you use a 24 pole switch you can wire it so it only affects that position.

All that said, the 500k really won't hurt your neck pickup. Neck position is darker by nature so a tad more brightness probably wont bother you.

 

[GuitarDoc]

Re: potentiometers question

Exactly wrong. You don't want a 250k resistor in series with your pickup, it will darken the pickup up like having a 500k pot rolled half way down.

Ray, let's not mislead the OP, now.

I'm not sure if I didn't fully and clearly state what I was thinking, or if you just didn't read what I said. But actually, having 500k ohms resistence instead of 250k ohms will brighten your tone, NOT darken it.

You know that a potentiometer (variable resistor) is just a resistor, right? And that the total resistence of several resistors in series is the sum of their resistences (R1 + R2 + R3 + etc). When a 250k ohm pot is full on it measures (within tolerences) 250k ohms. With a 250k ohm resistor in series between the pup and the 250k ohm pot you will get 500k ohm total resistence (with the pot full on). Certainly this will change the taper as the pot is rolled off, but it makes a reasonable compromise so that one pup will be connected to a 250k ohm resistence and the other pup will be connected to a 500k ohm total resistence. This is what the OP wanted to do...have his two pups see different resistences but with a single vol pot. He wanted his middle pup (Hot Rails) to see 500k ohms, and his neck (single coil) pup to see 250k ohms. He didn't want two pots and didn't want a concentric pot.

Please explain how else this could be done.

I don't mind being told I am "exactly wrong" if I really am, but back it up with some accurate proof, please. But as far as I can figure, I am correct and you are "exactly wrong". A higher resistence between a pup and the jack will give a brighter tone than a lower resistence (a 1 meg, 500k, 300k will all be brighter than a 250k).

 

[RayBarbeeMusic]

Re: potentiometers question

Then you figure wrong. Proove it? You are welcome to come by and I'll do that if you are near me.

But actually, having 500k ohms resistence instead of 250k ohms will brighten your tone, NOT darken it.

500k resistance between hot and ground, yes, 250k in series with your output, no. There is a big difference.

If what you say were true, you could get a REALLY bright pickup by putting a 22M resistor between the hot of the pickup and the switch right? Try it. Now what did we learn?

Please, get some minimal education in electronics before giving answers like that. I work on tube amps and guitar electronics all day long, what do you do for a living?

I really don't want to get into arguing with a layman who doesn't have the requisite knowledge to begin to understand the electronics. If you doubt my answer, hit any appropriate electronics technical forum and re-ask the question.

It does not require 2 pots, nor a concentric pot. You can do it with one 500k or 470k resistor to ground in PARALLEL. Which is the correct way to do it.

 

[idsnowdog]

Re: potentiometers question

Here is what wiring a 500K resistor in parallel would look like. You just solder a resistor from the hot lug to the back of the pot so the pickup sees two 500K loads in parallel which roughly equals 250K.

 

[RayBarbeeMusic]

Re: potentiometers question

Exactly.

That would also give you ~250k when the pickups were in parallel, as I said above, if you want it to only affect the one switch position, you can wire that easily with a 24 pole 5 way switch. Allparts sells them here:


http://www.allparts.com/4-Pole-5-Way-Super-Switch-p/ep-0078-000.htm

The default though is just try it with a 500k pot and see if that bothers you on the neck pickup. If it does, then add the resistor or change the switch and add a resistor; if it doesn't, you're set.

 

[GuitarDoc]

Re: potentiometers question

OK, I see where the miscommunication is. In my last post I said..."A higher resistence between a pup and the jack will give a brighter tone than a lower resistence (a 1 meg, 500k, 300k will all be brighter than a 250k)".

What I meant was..."A higher resistence (to ground) between a pup and the jack will give a brighter tone than a lower resistence (a 1 meg, 500k, 300k will all be brighter than a 250k)". But since we were talking about volume pots, I assumed that we understood that the resistence was to ground as is the case in the pot. I was NOT talking about a resistence in the hot wire from the pup to the jack, only refering to the pot's location between the pup and the jack.


Two 500k resistors in parallel gives a 250k resistence. Two 250k resistors in series gives a 500k resistence. Is this not correct?

Idsnowdog's diagram showing two 500k resistors in parallel (the vol pot + the resistor) for the neck pup is probably the best way to achieve a solution to the OP's question, but would it be wrong to have two 250k resistors in series for the middle pup (Rail)?

Are you still saying that a 500k or 1 meg vol pot is darker sounding than a 250k vol pot? Because that is what I was talking about. I did assume that you were very familiar with electronics and guitar layout, that's why I didn't spell everything out.

Sorry for the confusion that I may have created.

 

[James Davidson]

Re: potentiometers question

why does a higher resistance make the tone brighter? it makes sense to me that it would be the other way around for some reason. is it because the bass frequencies cause a bigger current in the wires or something and the higher resistance prevents them getting through?. i really have no clue about these things. i just solder the parts in and dont think about it.

 

[idsnowdog]

Re: potentiometers question

why does a higher resistance make the tone brighter? it makes sense to me that it would be the other way around for some reason. is it because the bass frequencies cause a bigger current in the wires or something and the higher resistance prevents them getting through?. i really have no clue about these things. i just solder the parts in and dont think about it.

A smaller value pot bleeds more treble frequencies to ground than a higher value. As pickups become more powerful in terms of resistance they often become darker sounding.

My general criteria:
4-6K = 100K - Danelectro Lipstick Tubes
6-8K = 250K - Most Strat/Tele Pickups
9-14K = 500K - P 90's, HOT single coils and most humbuckers
15-20K = 1Meg - Invader, Dimarzio Super D, Motherbucker, Dirty Fingers