Values for tone pots and cap in replaced electronics in guitar

[Dusty Chalk]

Sorry, newb still seeking advice. I'm having a tech install two (humbucker sized) P90s into a Custom 24/7, and I'm doing this mostly for the "bark" of P90s, so I want the tone controls to be least in the way of the pups as possible.

Based on these two articles: Dialing in the Passive Tone Control, and Swap that Tone Knob for a Warmth Control (thanks for the link to Mod Garage, by the way, Garrett), I've decided to go with 250K-ish tone and volume pots, and -- in trying to follow the advice of the article -- use a 1000pF to 6800pF cap, except my tech doesn't have anything like that, and his usual source only sells caps as low as 0.01 Microfarad for tone, and they have a treble bleed cap that's 0.001 Microfarad.

So what should I do? 0.01 Microfarad? He's kinda doing this for me as a favour, so I don't want to tell him to wire two 0.01s in series (yielding 0.005 Microfarad, or 5000pF, which would be in the middle of the recommended range).

I also read that 550K pots would make them brighter, is that true? It seems counterintuitive to me, but I'm still learning. Do I want 550K pots?

 

[andy474x]

500K (or thereabouts) pots are the standard for P90's (and humbuckers), 250's for Fender style single coils. Larger value pots bring out more high frequencies from darker/fatter sounding pickups like P90's and humbuckers. If you have a naturally bright sounding guitar, 250K's might be a good nod, but otherwise I would go for the 500's or 550's.

Regarding the tone caps, basically the value of a capacitor dictates the frequency at which it filters signal, anything above its target frequency gets filtered out to ground. Mix that with a variable resistance tone pot, and you're basically filtering out some fraction of the frequencies above that cutoff dictated by the capacitor, the fraction being determined by the setting of the pot. The smaller value tone cap you choose, the higher the cutoff frequency will be. Again, here I would make your choice according to the acoustic voice of your guitar. The brighter the guitar, the higher the value tone cap.

Have you tried looking at an electronics supplier for the part values you're after? Luthier supply sites usually don't cover a wide range of electronics parts values.

 

[Dusty Chalk]

Ah! Actually, it's a combination of the resistance and the capacitance, but the rest of your explanation helps me to understand much better. Thank you for that.

Also, no, I hadn't thought of contacting an electronics supplier. Thanks for that as well.

 

[Em7]

500K (or thereabouts) pots are the standard for P90's (and humbuckers), 250's for Fender style single coils. Larger value pots bring out more high frequencies from darker/fatter sounding pickups like P90's and humbuckers. If you have a naturally bright sounding guitar, 250K's might be a good nod, but otherwise I would go for the 500's or 550's.

Regarding the tone caps, basically the value of a capacitor dictates the frequency at which it filters signal, anything above its target frequency gets filtered out to ground. Mix that with a variable resistance tone pot, and you're basically filtering out some fraction of the frequencies above that cutoff dictated by the capacitor, the fraction being determined by the setting of the pot. The smaller value tone cap you choose, the higher the cutoff frequency will be. Again, here I would make your choice according to the acoustic voice of your guitar. The brighter the guitar, the higher the value tone cap.

Your understanding of guitar electronics is typical of that of a guitarist, but it is completely wrong. Larger value pots do not increase high frequencies. The frequency response of a pickup circuit is set by its inductance and capacitance. What larger values pots do is alter the ratio inductive to resistance (a.k.a. the q-factor) of the circuit, lowering the resonant peak and an evening out the circuit's response. That is not the same thing as increasing highs. An RLC circuit's q-factor determines how sharply the circuit's response drops off on both sides of the resonant peak. The major reason why a Strat quacks in positions 2 and 4 is because inductances add in parallel while resistances divide, increasing the ratio of inductive to resistance (a.k.a. the q-factor). A Strat pickup normally has a high resonant peak and the peak is emphasized in positions 2 and 4 because frequency response drops off much sharper than in positions 1,3, and 5. The higher the q-factor of a circuit. The more the resonant peak is emphasized.

Additionally, the tone cap does not act as a simple RC circuit with a cutoff frequency that bleeds high frequencies to ground. If the the tone cap did that, there would be a loss in volume as the tone control is rolled down. What tone cap does is add capacitance to the RLC (resistance, inductance, capacitance) circuit's capacitance shifting the resonant peak (the frequency at which the pickup circuit is loudest) down in frequency.