Where to find 250k fixed resistors?

DigiKey, Mouser, or Newark

Through Hole Resistors | DigiKey

https://www.mouser.com/Passive-Comp...MIqKP6z5eG2AIVhEpeCh0TDg_IEAAYAiAAEgKnuvD_BwE

http://www.newark.com/c/passive-components/resistors-fixed-value/through-hole-resistors

 

Resistors don't normally come in multiples of 25. Instead, they come in multiples of 10, 22, 33, 47, etc. What you want is a 220k resistor. Those are common and easy to find. You won't be able to hear the difference between 220k and 250k, but if it worries you enough, then you could add a 33k resistor, which is also easy to source.

 

Btw, the capacitor really is not necessary. You will get the same effect from a 100k resistor in series with a 33k resistor, instead of what you had planned.

 

DigiKey does not have 250k Ohm resistors, but Mouser does if that is what you decide to use. And as line6man says, you can combine standard values to add up to other values. You could also use a small trimmer pot adjusted to any value you want as well.

 

I drew that diagram a few years ago, to show how to wire a P bass with no pots, but the exact same "sound" as with the pots turned up to "10." That's essentially the schematic-equivalent of a P bass with the pots turned up to "10."

The interesting thing, however, is that when the tone pot is on "10," the capacitor no longer does anything audible in the circuit. You could replace the capacitor with a piece of wire, and it would still sound the same. So all you really need is the two 250k resistances parallel to each other. However, two 250k resistances in parallel is the same as a single 125k resistor, because of the way that resistance adds reciprocally in a parallel configuration. So a 125k resistor is ideal. Since this is an oddball value, you can just grab a 100k resistor and a 33k resistor and put them in series, for a total of 133k. This is not exactly 125k, but it is close enough that you could not hear the difference, and the pots you use in basses can vary by 10% or 20%, to begin with.

 

I came across this site a couple days ago: Standard Resistor Values » Resistor Guide
It has information about standard values of fixed resistors,.
The "Materials" tab at the top will give you some information describing a few of the common types of materials, construction, properties, and typical uses for the various types of resistors.
Even though I mentioned a trim pot, I would use fixed resistors myself if I planned to do what you have in mind.
I recommend that you use metal film resistors. Don't worry about Wattage or Voltage ratings for this application.

 

I've been happy for years buying parts from Antique Electronic Supply tubesandmore.com. They've been fast and accurate and very reasonable WRT cost.

 

220k is close enough. This is a project requiring $0.08 worth of resistors.

You're not buying a 0.1 % tolerance capacitor, are you?

 

I love dialing in exact values when it makes a difference but in this case either 220k or 270k which are standard values for 10% fixed resistors would be plenty close enough. One or both of those suppliers likely have 240k, which is a 5% standard value, and 249k which is a 1% standard value.

 

You can also wire in a pot as a variable resistor, and select the exact resistance to dial in the brightness on the fly. Less pronounced than a tone knob, but still useful to tame harsh highs (esp. on new strings). It also lowers your volume bit (just like fixed resistors would), and it works as an on/off switch at the end of the turn. Of course, if you don't want to have any controls, a trimpot would work the same.

 

220k is a standard 20 percent or 10 percent value. Nowadays, 5 percent resistors (or 2 percent) are dirt cheap, and 240K is a standard value in those tolerances. Or 270K. As the pots were 20% back in the (meaning they could be anywhere from 200K to 300K and be "good"), either of those values is definitely in the window. If I were you, I'd go with 240K.

If you're going to wire one of the resistors from hot to ground, and the other one in series with a cap from hot to ground, I'd suggest you skip the capacitor, and just wire one 120K resistor (the value you get from paralleling two 240 K reistors) from hot to ground. It'll be 99.999 percent the same as the 3 part thing you're contemplating (honestly, you'll never hear the differnece), and be much simpler to wire - you can just wire it across the output jack, and you won't have a hanging node (that part of the circuit where the second resistor and the cap hook up to each other) to figure out what to do with.

 

Yep, 249K shouldn't be hard at all to source. A quick look at Mouser shows over a dozen 1/4 watt options currently in stock, and that's just the metal film ones.

 

One more idea...replace your standard pot with a trim pot. You can set it exactly where you want it with a screw driver and here is no shaft or nob, and forget it.