Correct volume pot value for strat and HB pickups

[josesrv]

Hi everybody. There is a rule to use 250k ohms volume pots on stratocaster pickups (from 5.5k ohms until 7.5k ohms resistance values), and to use 500k ohms on standard humbucker pickups (generally between 7.8k ohms until 9k ohms resistance values).
The questions are:
1 - Why is this correct? Is that because needs to be a relation between pickup value in resistance, inductance and/ or impedance with the attached volume/resistance pot?
2- What really happen if I change that generally used value in case of a strat from 250k to 100k or to 500k, and the same for a hb to 300k or 1000k? Does it ruins the pickup tone someway, or what?
Many thanks for any light on this matter.:

[David Schwab]

Lower value pots smooth out the top end a bit and tend to sound warmer. Higher values sound brighter. Since humbuckers are often wound hotter than single coils, they use higher value pots. But there is no right and wrong. Seymour Duncan often recommends 250K for humbuckers.

100K would only be usable for low impedance pickups.

[bajaman]

good points David.
You could always use 500k pot and connect a 470k ohm resistor (or lower value perhaps) across the #1 and #3 terminals.
If you solder one connection and use an alligator clip for the other connection, you can hear the effect of 500k or 250k soundwise - only when the pot is at full volume though.
Sometimes small capacitors in the 47pf to 470pf range ( connected across the pot terminals as above) can tame otherwise brittle sounding pickups even when using 250k pots too.
Use your ears - the best measuring instrument available - and tweak away.
cheers
bajaman

[Mark Hammer]

Although the complementary loading effects of different value volume pots for different types of pickups are well-founded, their value in doing so will depend on how you use them.

A 500k volume pot will preserve more treble when turned up full (hence its desirability for treble-challenged HB and P-90 types, and frequent nondesirability for SC types), but once you start to turn down, all those advantages disappear as that portion of the pot resistance between the input lug and wiper is effectively added to the pot DC resistance.

If one is the type of player that generally leaves the volume up full and only rarely turns it down (e.g., to placate a singer or ask "What'd you say?"), then the 500k-HB/250k-SC rule of thumb makes eminent sense. If you're a player who is constantly fiddling with the volume pot, then consider something outside that box...or switch to a volume pedal instead of the guitar control. Alternatively, consider use of various parallel components, as escribed in eaqrlier posts, to achieve the dsired tonal outcome.

FWIW, I like to use as high a value pot as I can w/SC pickups, simply because I can always carve away whatever treble I don't want, but it's hard to recover if you've shut yourself off from it by commiting to 250k. I, too, fiddle with my volume control, but use compensating caps to offset that.

[Rick Turner]

I usually put in an "all pots bypass" switch in passive instruments using a push-pull volume pot. Pop it out, and no loading what so ever from the pots or caps in the instrument. You get this little kind of turbo boost to the sound.

Ry Cooder used to (and maybe still does) like 1 meg pots in his guitars for less loading.

[FunkyKikuchiyo]

I never found going way up on pot values to be all that liberating. They won't change the voice of a pickup, just add highs. Most of the time they are highs that are best left out. I DO find it useful to check pot values before installing and not just assuming that the stamped value is true. I've pulled out 500k pots that turned out to be 330k pots and made a guitar super honky.

I have found that putting a resistor in parallel to a single coil when you use 500k pots for the sake of a humbucker (like a tele with a HB in the neck) to be a nice little modification. So often those can be hard to set up - muddy neck, ice pick bridge... this lets you get a bit of a compromise. It messes up the middle position a bit and makes it a tad too dark, but it is still usable. If it really bugs you, then you can get a fancier switch.

bajaman - good call on the alligator clip thing. I did that for a client a while ago who was asking about pot values - I think it was far better than me going on and trying to describe it.

[Rick Turner]

Yeah, I guess paying attention to what clients like Ry find useful is really stupid...

[Steve Conner]

Paying attention to what Eric Johnson wanted, now that would be stupid.

Rick, can you recommend any particular brand of push-pull volume pot that would be good quality? I like that idea.

Talking of adding extra loading components: Many old amps have an input impedance of 136k when you plug into the "low" jack, and 1M when you plug into the "high" one. I find that the 136k loading makes the pickups sound warmer, but gives a more consistent tone with less treble loss as the guitar volume is turned down. On the 1M input it gets muddy really quick.

[Rick Turner]

I just use the fairly generic push/pull pots that I can get in bulk for decent cost from AllParts. Unfortunately, I don't think we really have a lot of choices in this area, so I just use what I can get.

[pdf64]

See link for some really helpful info on this topic
BuildYourGuitar.com :: The Secrets of Electric Guitar Pickups

[josesrv]

compensating caps

Although the complementary loading effects of different value volume pots for different types of pickups are well-founded, their value in doing so will depend on how you use them.

A 500k volume pot will preserve more treble when turned up full (hence its desirability for treble-challenged HB and P-90 types, and frequent nondesirability for SC types), but once you start to turn down, all those advantages disappear as that portion of the pot resistance between the input lug and wiper is effectively added to the pot DC resistance.

If one is the type of player that generally leaves the volume up full and only rarely turns it down (e.g., to placate a singer or ask "What'd you say?"), then the 500k-HB/250k-SC rule of thumb makes eminent sense. If you're a player who is constantly fiddling with the volume pot, then consider something outside that box...or switch to a volume pedal instead of the guitar control. Alternatively, consider use of various parallel components, as escribed in eaqrlier posts, to achieve the dsired tonal outcome.

FWIW, I like to use as high a value pot as I can w/SC pickups, simply because I can always carve away whatever treble I don't want, but it's hard to recover if you've shut yourself off from it by commiting to 250k. I, too, fiddle with my volume control, but use compensating caps to offset that.

Hi Mark: I usually use 250k pots on my SC pickups, but I found out that a 500k vol pot (with a treble bleed) is usable if you like the extra treble (I prefer a sound with less trebles like the one obtained thru 250k vol pots)
As you mentioned above, I also use frequently my vol pot the reduce gain, What are the compensating caps that you use and how are they connect it?
Rgds,
José

[jrfrond]

The issue with using too high a pot value is that very often, the response of the pot as you turn down can be compromised, that is IF you care about a smooth transition from low-to-high volume. Pot tapers are piss-poor enough as it is nowadays. RS pots are the best I have found in affordable volume pots. If you can find true log taper pots from Presion Electronic, or NOS Allen-Bradley, Clarostat or Ohmite, those were best. I know that Rick will agree with this from the Alembic days.

I agree with Mark that loading a pickup with a pot is a poor way of tone shaping, but hey, if it's "your sound", then why not?

Fender had CTS make "No-Load" volume pots, which basically shorted the wiper to the hot leg at the top of the pot travel, taking the VOLUME pot resistance out of the circuit, with the tone pot left in, which means that, although it's an AC signal path, there is still rolloff from loading.

Rick Turner's "blow switch" (as I like to call it), is really the best option if you want maximum fidelity.

Having said all this, I would use 500K for a HB/SC guitar.

[Mark Hammer]

The compensating cap acts as a bypass around the volume pot for treble content. It goes between the input lug and the wiper of the volume pot.

Ordinarily, the volume pot acts as a voltage divider for the entire signal, such that, for instance, if the wiper was set to a position where there was 250k on one side of the wiper and 250k on the other, the signal at the wiper would be one half of what was fed into the pot. For higher frequencies, though, the capacitor acts likea zero-ohm path, so that instead of 250k/250k, you have what is essentially 0-ohms/250k at that same position. The rest of the signal might be attenuated, but treble content is not.

Now, the thing to remember is that the bypass cap is not like a brick wall. The obstruction it poses to frequency content decreases gradually, as you go up the spectrum. The larger the cap value, the lower that gradual change begins. So people select cap values commensurate with what they want to preserve. I lean towards higher values, simply because I like scratchy Motown/Johnny "Guitar" Watson guitar tones. Having a high value, like 1500pf makes the volume pot function sort of like a bass rolloff by retaining so much of the mids between the 10 and 7 settings on the volume. A value like that can also be helpful for folks who have a HB in the bridge position but also want to do chicken-pickin now and then. I also find that it tends to enhance "pinky swells" by introducing not only more volume, but more "body" as well, when you quickly rotate from volume off to volume on. But again, that's my own taste, and isn't necessarily what I'd recommend to everyone.

Of course, if the intent is simply to retain roughly equivalent bandwidth between the fully on and 5 or 6 settings on the volume control, then more conservative approaches are required. What is often recommended is use of a 1000pf (.001uf) cap and a 150k fixed resistor between input and wiper lugs. It is described nicely here: Guitar Technology

I suppose another matter that comes up is whether the sorts of tonal adjustments and compensations applied to neck pickups are really appropriate for the bridge pickup, and vice versa. I can see where someone might want to have compensation for the bridge pickup, but not for the neck one; after all, few people select the bridge pickup for subtlety or background qualities, where they might turn the neck PU down for background rhythm strumming and perhaps appreciate the effect that loading has on softening the treble. Personally, I've been a staunch advocate for different tone caps for neck and bridge tone controls for some years now. But of course, if the guitar only has a single master volume control, then one needs to consider whether the compensation used strikes a suitable balance between what you need for the neck pickup, and what you need for the bridge. Use your judgment, and don't be afraid to experiment.

[jrfrond]

I believe PRS used to have a rolloff cap on a switch to simulate loading, calling it a "sweet switch". I never opened a PRS that had it to check it out, but it seemed like that is exactly what it did.

Never really liked the bright cap/resistor mod, but that's just me. It really needs careful tailoring to not sound "icepicky", and it always seems to be a fine line.

Personally, I think that "full fidelity" on a guitar is highly-overrated. It is for this reason that I've always modded my own Strats with a jumper on the switch to enable the tone control for the bridge pickup, because unloaded, the tone is just too brash to my ears.

[Mark Hammer]

.....and that's why I keep emphasizing personal preference in whatever one does with respect to compensating. Maybe it's my love for ice-picky tone and "scratchy" guitarists like Nile Rodgers or Randy Jacobs, or maybe its hearing loss from my teenage years working punch presses in machine shops, or simply age catching up, but what some folks just hate about compensated volume pots, and using 500k/1M pots with SC pickups, I love. Doesn't mean others have to, though.

The trouble is, Fender sure never made it particularly easy to "season to taste" on a Strat, did they? Not like a control cavity on a Tele that you can piddle with while the instrument remains strung up. I'm still waiting for those "mod-friendly" two-piece Strat pickguards, like they have on a Jaguar or Mustang. So I can well understand the OP's desire to know, in advance, what the "correct" component values are.