Single 250k vs two 500k pots

[AM]

Hi,
Not a stompbox but pickup installation related question. I'm changing my Tele's pickups from single coils to humbuckers. The guitar has stock 250k pots but the tone pot features a no-load pot. So when all the way up the tone pot is essentially out of the circuit. I'm thinking about keeping the stock pots and not change them to 500k as many humbucker guitars have. I read somewhere that a 250k single volume pot has the same effect on how the pickups sound as a 500k volume combined with a 500k tone pot. Is this correct?
Thank you

[Mark Hammer]

Sort of...though not exactly.

Ignoring a whole bunch of stuff, if a person had a 500k tone pot turned up to max treble (i.e., presenting a 500k path to ground....through a cap), and a 500k volume pot turned up to max vol, and it was the traditional arrangement of the tone pot wired to the input of the vol pot, then yes, a pair of parallel 500k resistances to ground IS equivalent to 250k to ground.

However, IF you move your volume pot away from max vol or your tone pot away from max treble, then it runs into something different.  Moreover, because the tone pot represents a 500k path to ground only for that frequency content that will pass through the cap, but not for content lower in frequency than that, it never really was "just" 500k to ground.

The received wisdom is that, when the pickup starts out with more top end, a lower resistance volume pot will help to "load down" the pickup in a helpful way to eat up some of the objectionable top end, and when the pickup does not have quite as much top end, a higher value voluem pot will not load quite as much and preserve more of the top end.

My view is that, while this is correct, provided the volume controls are left on full and never touched, once you move the volume pot down, even a bit, all loading/unloading considerations go out the window.  If you're the type of player who tends to leave the volume control up all the way except for when you want to lean the guitar against the amp, follow the received wisdom.  If you're the type of player who is frequently fiddling with your volume pot, just stick with whatever you have in there now, because changing it won't matter.

[AM]

Thanks Mark. I was a bit surprised when you said that if I use the volume knob a lot I should just leave the 250k pots there because it won't matter if I put 500k.
I do use the volume pot a lot. Especially for volume swells. I practically never use the tone pot. So I was thinking since I never use it and it has the no-load feature I could just throw the humbuckers there and leave the stock 250k volume pot and achieve pretty much what a pair of 500k vol/tone pots would have as an effect on the pickups at max settings. My concern is basically when I would lower the volume pot if the overall sound would be too dark comparing to what it would be if I would lower a 500k volume pot. 

[GGBB]

That's not entirely accurate.  With conventional wiring and both 500K tone and volume pots full up, it is the same for frequencies below the crossover point of the tone control (which is dependent on the pickups, amp input etc.).  Realistically no practical difference.  But when you start factoring in adjustments to the pots, it's no longer the same because you are dealing with a single series resistance voltage divider versus two parallel resistances with one of them being a voltage divider.  Someone more brainy than me might be able to explain the details a little more clearly than I.

Mark (brainier than I) beat me to it.

But that doesn't mean it's a bad thing or that it won't sound good - it might not be at all noticeable.  I use 250Ks on my humbuckers and I quite like them that way.  Les Pauls used to use 300K pots which is closer to 250K than 500K.

[Mark Hammer]

Thanks Mark. I was a bit surprised when you said that if I use the volume knob a lot I should just leave the 250k pots there because it won't matter if I put 500k.
I do use the volume pot a lot. Especially for volume swells. I practically never use the tone pot. So I was thinking since I never use it and it has the no-load feature I could just throw the humbuckers there and leave the stock 250k volume pot and achieve pretty much what a pair of 500k vol/tone pots would have as an effect on the pickups at max settings. My concern is basically when I would lower the volume pot if the overall sound would be too dark comparing to what it would be if I would lower a 500k volume pot. 

When you lower the volume, because the volume pot is a voltage divider, you are doing two things at once.  First, you are placing additional resistance in series with the pickup.  Second, you are placing a low resistance path from hot to ground.  If all you did was just change 500k to ground to, say, 346k to ground, you would still load the pickup down a little more, but you would not be sticking anything in series with it.  However, you are doing both whenever you turn the volume down.  It is that series resistance that kind of renders the pot value moot.

Fender's solution was to use a compensating cap, straddling the input lug and wiper of the volume pot, such that the cap would provide a zero-ohm path for higher frequencies...which is precisely the content you worry about losing when you load down the pickup.  While not a common solution, there is no law that say you can't compensate a 500k volume pot on an HB-based guitar.

[pappasmurfsharem]

Thanks Mark. I was a bit surprised when you said that if I use the volume knob a lot I should just leave the 250k pots there because it won't matter if I put 500k.
I do use the volume pot a lot. Especially for volume swells. I practically never use the tone pot. So I was thinking since I never use it and it has the no-load feature I could just throw the humbuckers there and leave the stock 250k volume pot and achieve pretty much what a pair of 500k vol/tone pots would have as an effect on the pickups at max settings. My concern is basically when I would lower the volume pot if the overall sound would be too dark comparing to what it would be if I would lower a 500k volume pot. 

When you lower the volume, because the volume pot is a voltage divider, you are doing two things at once.  First, you are placing additional resistance in series with the pickup.  Second, you are placing a low resistance path from hot to ground.  If all you did was just change 500k to ground to, say, 346k to ground, you would still load the pickup down a little more, but you would not be sticking anything in series with it.  However, you are doing both whenever you turn the volume down.  It is that series resistance that kind of renders the pot value moot.

Fender's solution was to use a compensating cap, straddling the input lug and wiper of the volume pot, such that the cap would provide a zero-ohm path for higher frequencies...which is precisely the content you worry about losing when you load down the pickup.  While not a common solution, there is no law that say you can't compensate a 500k volume pot on an HB-based guitar.

Pretty sure my Ibanez JS1000 has this or something similar. The volume pot is push pull and engages a high pass filter when pulled. Doesn't much of anything at full up, but when rolling off real low volumes it allows the guitar to still sing and chime.

[AM]

Thanks gents! Your input is much appreciated.
Mark your second post cleared everything for me. I'll leave the 250k there and see if I like it.

[ashcat_lt]

Moreover, because the tone pot represents a 500k path to ground only for that frequency content that will pass through the cap, but not for content lower in frequency than that, it never really was "just" 500k to ground.

Of course, for the frequnecies of interest in this situation the cap looks like a short, so it really pretty much is...  The "loading down" effect is mostly interaction with the inductance of the pickup coil.  For most of the rotation of the T pot you're hearing that RL low-pass happening.  It's not until you get way low on the knob that the cap starts to interact with the series resistance of the coil to make an RC lowpass, or more correctly I guess an RLC filter where you start to see the resonant peak start to poke up again.

Turning down the V pot tends to isolate the L behind the series section of the pot, so that it doesn't really respond to the "loading" of the reduced parallel resistance quite so much, but at the same time that series R works with the C in the cable as yet another RC low-pass, which tends to have a very similar effect.