BGWN: I suspect the way things work with those numbers seen on Gibson pots is that they are some kind of part number and instead of identifying a specific Kohm value, they may instead just simply indicate either the tone pot or volume pot of that day, that era. There was a time when they did use 300K volumes and 100K tones, 300Ks starting around July 1973 and later 100K tones. In having looked at various Gibson pots, here's what I noticed in terms of part numbers and values:

44071079 - long shaft "tone" pot, 100K audio in very late 70s through mid 1980s, 500K audio in 1990s up until today
44070034 - long shaft "volume" pot, 300K linear
44070028 - short shaft "volume" pot, 300K linear
44070035 - short shaft "tone" pot, 500K audio
44070500 - short shaft pots, 500K, used in recent Historics, the pots with the scary plastic insides

Les Paul Forum Member
I just ordered 6 CTS pots to upgrade my Y2K 59. I ordered 6 because I of the variances in resistance. Since I can only use 4 (and I'm assuming that I use the top 4 in the list), is there an optimum position for the pots?

BGWN
Yes I would use the two largest value pots for the volumes, and the next two largest for the tone controls. The largest value would likely be best used with the bridge pickup. I would also suggest that you review the thread from a little while back in the Tone Zone area titled "new insight into pots". There I describe how you can mod the pots to increase the value of the resistance, get any pot that measures well down in the 400K range up to 500K or maybe more.

Les Paul Forum Member
Ok, what about lowering the resistance? I have a couple of older cts and an old gibson that measure upwards of 600K. It's funny how these vary so much. I had an SG from the early 70s that had a pot actually measure 710K!

BGWN
You can achieve a lower net resistance, for the purpose of tweaking to get just the right amount of pickup loading, by using a resistor in parallel with the pot in question typically a volume pot. The math of resistances in parallel could be expressed such that the sum of the inverses of the resistances equals the inverse of the net resistance, did you follow that? In more symbolic algebra terms, using Rpot, Rextra, and Rnet: (1 / Rpot) + (1 / Rextra) = (1 / Rnet)

For example, if you had a 500K pot and stuck a 1Meg resistor in parallel with it, the net result would be 333K. A 600K pot with a 1Meg parallel resistor would produce a net 375K. I put a 1Meg audio pot in my R9 for the bridge volume pot, intended for using higher output pups, but I later added something like a 1.5 Meg resistor in parallel to get a lower net value around 600K when I switched to trying a more traditional pup such as an Antiquity.

Les Paul Forum Member
While you're crankin' out the goods... Could you explain why a guitar sounds brighter with no tone pot versus the same guitar with a tone pot set on 10? Is that enough loading to make the difference? Also, if you have two guitars setup exactly the same except one guitar has a 500K tone pot and the other has say a 250K tone pot (or whatever), would there be a difference in sound if the tone controls were set on 10 on both guitars? Why?

Also, does the resistor mod you mentioned above mess with the taper of the pot any? i.e. if you have two pots that both measure 500K, and one is a normal pot and the other is a pot with the "resistor" mod, would they both put out an equal amount of resistance at a setting of say 5 for example?

BGWN

In the past some have commented that their head aches after reading one of my explanations, that they needed an aspirin. As such you have all been warned. Okay here goes...

Let's start with your first paragraph, the no tone pot versus tone pot set on 10. First when you said "When on 10, a pot usually seems to measure around 1K to 3K ohms.", that does not exactly make any sense. A pot is a resistance with terminals or connections at either end of the resistance, plus a third middle terminal that goes to a wiper that makes contact somewhere along that resistive track. When on 10, full on, a pot should measure close to 0 between the the middle wiper contact and one end, while the full value of the pot between the wiper and the other end. Typically there will be some residual contact resistance even at full on, but it probably should be less than about 75 ohms. As such with a volume control the input to output wiper terminal connections should measure close to 0 (typically less than 75), while with a tone control the opposite sort of arrangement is used, the measurement would be the full value of the pot, 500K or whatever.

Okay, as to the "to tone pot or not to tone pot". First keep in mind how a capacitor behaves, the higher the frequency of a signal the lower the impedance or resistance of the cap. With the tone control set to minimum you have the tone capacitor in parallel with the pickup/volume pot, so the mid-higher end frequencies get "shorted" to signal ground. As you turn up the tone control you are introducing some resistance in series with the tone cap, which progressively reduces the effect of the tone cap. When you have the tone control on full the amount of resistance added in series with the tone cap is sufficient to make the tone cap's effect relatively neglegible. With a volume control you really are turning up the volume, turning up how much of the signal you are selecting. However with a tone control in a sense you are not literally turning up the tone rather it's a kind of reverse logic, turning down the tone you are increasing the removal of the higher frequencies while turning up the tone you are turning up the *elimination* of the removal of the high end.

Now with the tone control full on... If you consider what the situation would be for the higher frequencies, where the impedance of the cap is relatively small, effectively you still have what amounts to a 500K tone pot in parallel with the volume pot. As such the net loading on the pickup is two 500K resistances in parallel, thus only 250K. The point is that even with the tone control full on there is still a small loading effect on the pickup at the higher frequencies. If you then disconnect the tone pot/cap, the loading on the pickup becomes only that of the volume pot, 500K or whatever. This would better allow the natural responsiveness of the pickup to be realized. Somewhere on the Seymour Duncan web site they had some graphs of pickup output versus frequency response. The variable between each graph was the amount of loading applied the pickup, 100K, 250K, 500K, 1Meg, or an open circuit virtually no load. The results were that the upper mid response of the pickup was reduced by the excessive loading of the 100K and 250K pots, while the larger value pot/lower load allowed the upper response to be better seen. Note that it might be quite possible to go too far. Some people have tried using the lower output cleaner weaker pickups and found that without a tone control or with a 1Meg volume they start to sound too harsh, too brittle, not quite right. What they are probaby describing is the upper mid response of the pickup being allowed to become too pronounced for their tastes.

The loading effect is due in part to the idea that a guitar pickup is NOT a low impedance device able to cope well with any serious load. Let's digress and use the audio power amp for an analogy. An amp that may be fine for an 16 or 8 ohm load may get into some trouble if you try to drive a 4 or 2 ohm load. There is an internal "resistance" of the output stage of the power amp. Say it was 1 ohm. If driving a 16 ohm load then 16/17 of the power output would go to the load with 1/17 dropped across that internal 1 ohm resistance, if driving an 8 ohm load then 8/9 of the power gets used. However if you tried using a 4 ohm load, only 4/5 of the power gets to the speaker, 20% gets wasted in terms of heat in the amp. If you tried a 2 ohm load the situation gets worse. Generally speaking pro audio PA power amps that can handle 4 or 2 ohm loads have to have a serious output stage with many output power transistors in parallel to get the internal resistance of the amp down to a small fraction of an ohm.

The analogy applies to some extent with passive guitar pickups. A traditional PAF style pickup with 42 gauge wire having a total coil resistance of around 8K may be okay with those 300K pots Gibson has been using in the production LPs. If you wanted to keep the loading effect to a minimum you probably would want to have at least a 35 or 40 to 1 ratio between the value of the pot and the pickup coil resistance, just my rough rule of thumb. Once you start getting into the Gibson 498T/500T or the various stronger wound higher output Seymound Duncan models (JB, Duncan Custom, Custom Custom, Duncan Distortion), with windings in the 13K to 16K range or more, a case can be made that a 300K pot is an excessive load, too small of a pot, 500K is called for, and a 1Meg could even be justified. Part of the effect with pickups is also due to the very fine wire gauge used in the coils. AC power or higher power speaker cable will be up in the 18 / 16 / 14 gauge area, while pickup coil wire is way down in the 42, 43, or 44 gauge. You cannot get all that much current happening through a piece of 42 gauge wire before it would overheat and self destruct. The light gauge coil wire contributes to the pickup being sensitive to the pot loading effect.

Regarding pickups and coil wire, if you took a regular humbucking pickup and wound the bobbins crammed full with traditional 42 gauge wire, you could only get maybe a total of 9.5K of wire to fit. If a pickup measures over 10K, it would have to be using a lighter gauge wire, probably either 43 or 44. All other things being equal a pickup wound with lighter 43 or 44 gauge wire might exhibit a slight loss in response for the higher frequencies compared to 42 gauge wire. As a result most pickups that are wound somewhat on the strong side using 43 or 44 gauge wire also use at least an Alnico 5 strength magnet or an even stronger ceramic magnet. The Gibson 498T and 500T both use 43 gauge wire, and considering the typical resistance reading of a 500T the wire must really be crammed in there. The Duncan Distortion uses 44 gauge wire.

If you have swallowed all of this up until now, you probably could answer the questions in your second paragraph. If using a 500K versus 250K tone pot, the 500K pot would produce a slightly livelier or brighter tone. The reason would be that the 500K pot would be a lower load on the pickup than the 250K pot.

With the last question, let's compare say a 500K pot to a 1Meg pot with a 1Meg resistor connected across it to produce a net 500K resistance. Typically this concept would only apply to a volume control. In general the idea with volume pots is not the exact amount of resistance between the wiper and the end terminals, but rather an issue of RATIOS. A volume pot is used to pick off a portion of the signal, thus the full term potentiometer. You may also hear the electronics phraseology of voltage divider. If you had a 500K pot set such that the wiper to end terminals resistance was exactly half of the total, 250K, the output terminal would have 250K to ground while the input terminal would have 500K to ground, so the output would be half of the input signal voltage. Thus the resistive element of the pot with the adjustable wiper allows a portion of the signal to be picked off, based on the ratio of the resistances. If you had a 1Meg pot similarly set to have 500K from the wiper to each terminal, similarly you would have a voltage divider such that 500K out of 1Meg or half of the input signal would be at the pot output. The resistance values are different (double in this case) but the ouput/input ratios involved are the same, that's the idea at work with a volume pot. If we had an external 1Meg resistor connected across the pot, the pickup would "see" a net load of 500K, but the voltage divider function of the pot remains relatively unchanged.

By the way there are some assumptions being made with some of this, the downstream device in the signal chain would have to be a relatively high impedance to not interact excessively with a guitar volume pot and complicate matters. Tube preamp stages tend to be fairly high impedance beasts.

Les Paul Forum Member
To achieve the before mentioned 333k, would the 1meg resistor go across the outer lugs of the pot or between the signal and the pot? What if you modified a tone pot instead of a volume, would the math be the same or would the capacitor in series effect the formula? Would the p/up 'see' the same loading effect as it would with a volume pot?

Les Paul Forum Member
I hope I've got things down, and would like to ask a couple other questions if you don't mind.

1. Say a player has 500K tone and volume pots and they ALWAYS leave the tone control on 10 and just decide to disconnect and/or remove the tone control from the circuit to simplify things, BUT they still want the loading effect of the tone circuit on 10. Would it be correct to wire a 500K resistor in parallel with the volume pot (or switch over to a 250K volume pot)? Or to simulate that sound, would it be necessary to also put the cap in series with the resistor? From what you said, I don't think the cap has much effect when it is in series with 500K of resistance, so it probably wouldn't be necessary except for maybe the most esoteric ear.

2. What would be the difference in sound between a guitar with a 500K volume pot full on vs. a guitar with a 1meg volume pot full on? It seems that since the resistance would be essentially O on both when full on they would sound the same. The differences between the two pots would be noticed throughout the taper/input-output ratio. And the 1meg pot would get...darker?? before it is finally shorted to ground and silenced?? Since 1meg of resistance is more than 500K of resistance?

If I am not on the right track, would you so kindly try to smash the correct info into my thick skull?

BGWN
Let me try to respond to each question... Where I mentioned connecting a resistor in parallel with a pot, such as a 1Meg resistor in parallel with a 500K pot, I'm talking about connecting it "across" the resistive element of the pot. Typically with most pots, the three terminals line up and the middle terminal goes to the adjustable wiper. In a volume control application to connect an external resistor in parallel it would go between the outer two of the three pot terminals, in other words the two other than the middle wiper terminal. In terms of the signal connections, this would be between what is normally the input to the pot and signal ground.

With a tone control, if you really wanted to reduce the maximum value of the resistance, reduce the full on value, it would be best to connect the external resistor between the two pot terminals that are actually used. The idea still applies, if you had a 500K tone pot and stuck say a 2Meg resistor in parallel with that, that would produce a net maximum 400K resistance. I expect you still have all of that _in series_ with the tone cap going to the volume pot.

Note that putting a resistor across the volume pot increases the pickup loading flat right across the frequency spectrum. However adding a parallel resistance to the tone pot is more subtle as you still have the tone capacitor still in series with all of that. As such the loading effect of the tone control is not quite as significant or dramatic as the volume control, but it does play a part.

Les Paul Forum Member
Turns out the pots measure about 1 to 3 ohms when full on.

BGWN
Here goes, deep breathe... By the way, that is quite good, with some 500K pots you may see the full on resistance between the wiper and input terminals up around 75 to maybe 100 ohms. If I see that, I would try cleaning the pot wiper and resistive element, that often helps. For pots used as volume controls you want that as low as possible, below 50 ohms should be fine. I might guess the pots you were checking were fairly new, clean wiper contacts.

As to your question 1, no you may have missed the point. If you wanted to disconnect the tone control but retain the same behaviour and pickup loading, you would need to have the equivalent of what was originally there, a 500K resistor AND the tone capacitor (by the way the closest standard resistor values would be 470K or 510K). When you said "From what you said, I don't think the cap has much effect when it is in series with 500K of resistance, so it probably wouldn't be necessary", I think you missed a key point about the _frequency_specific_ pickup loading of the tone pot/cap. You have to visualize the state of the tone pot/cap combo at various frequencies. At lower frequencies you would have a 500K tone pot in series with a relative large cap impedance/resistance, so yes the whole thing is basically insignificant. At midrange frequencies you would have a 500K tone pot in series with some cap impedance, say maybe another 500K, so that would be a tone pot/cap of about 1Meg in parallel with the 500K volume pot (333K net load). At the highest frequencies you would have a 500K tone pot in series with a relatively low cap impedance approaching some small value, so that would be a tone pot/cap of about 500K in parallel with the 500K volume pot, 250K net load. You see now that you just can't disconnect the tone pot/cap and say it's the same as it being left set on 10 full on?? In some cases the difference is very subtle hardly noticeable, while in other cases it makes quite a difference.

Those who have been around here for a while have heard RICH rave about disconnecting the tone pot/cap when using the stronger pickups. That would leave JUST the 500K volume pot loading, so the loading would be 500K consistent across the frequency spectrum instead of the loading being progressively increased starting at some mid-upper frequency. Ah-Ha! If you have a pickup with a somewhat darker or mid rangy tone such as the SD Custom Custom, or some kind of "hot" PAF style pup wound up around 9K, if you use just a 500K volume pot you would likely get an enhanced higher end response. With the stronger pups they get some extra life, zing, crunch. I think the 498T in Gibson LP Standards and Customs wails much better with a 500K volume pot, instead of the stock 300K, and the tone control disconnected. I recommend any and all production LP Standard/Custom/Classic that you care about should get a 500K volume at least for the bridge pickup, and maybe the nail polish disconnecting tone pot mod, very highly recommended. Seriously, like they say about Amex, do not leave home without it!

As to your question 2, once again you seem to be missing the whole point of the pickup loading issue. Going from a 500K to 1Meg volume control with both full on might not make a noticeable difference depending on the pickups and amp, but the 1Meg pot would at least be a lower load. The difference is much more noticeable if going from those stock 300K volumes (or anything lower, 250K or God help us 100K volumes) up to 500K volumes. With a lot of pickup and amp combinations, after moving up to a 500K volume you are getting to the point where you don't have much more to gain from going higher. However, with the strongest pickups having ceramic magnets such as the 500T and probably the SD Duncan Custom and Duncan Distortion, you can get even more oooomph out of the tone if using those pickups with a 1Meg volume and a good tube amp. I believe RICH went as far with one guitar as using a 500T with a 1Meg volume AND disconnecting the tone pot, he maxed out!

However I should mention that there may be other noticeable side effects of going to a 1Meg volume pot. Depending on the amp first stage preamp, you may find the volume drops off a bit more quickly as you roll back the pot, and some find they lose some "sparkle" or top end as the adjust the pot to a lower mid setting. There are ways of dealing with that if necessary. The "treble bypass" or "treble bleed" mod involves putting a capacitor between the input and output terminals of the volume pot. A suitable value would be something between 470pf up to 820pf.

Les Paul Forum Member
It's funny this post came up, because just a few weeks ago I had to replace the bridge tone pot on my lester. The original Gibson pot in this 18 year old measured 388k, I assume it was supposed to be a 300k pot. But who knows, maybe it was a 500k that badly missed. Anyway I installed a CTS 500k (the vol. measures 528k) to replace this tone pot and the change was not to my liking. The CTS measures 510k. Rather than get a new 300k Gibson (yuk), this little mod seems like a better alternative to load the p/up more and lose a bit of the upper mids.

Les Paul Forum Member
I still say the simplest solution for the tone-pot-disconnect is just to put in a push/pull pot wired to disconnect the tone pot. Up: no tone pot. Down: Back to normal. (Or vice versa if you prefer, just wire it opposite.). At least this seems easier to me than opening up a pot for the nail polish trick. But then again I've never tried the nail polish trick so take that with a grain of salt. And thanks, BGWN for another tour-de-force in passive electronics mathematics. I count myself among those who understood most of it. I think... Seriously the formula for calculating net resistance will be of great use to me. I also think I'm going to slap a 1 meg pot in the R9 tonight to see how that brightens up the 500T.

BGWN
There was a time going back to the mid 80s or so when for a while Gibson commonly used 300K volumes and 100K tones (gulp)!. That might have worked for a fairly weak rather bright pickup, but I dunno... If with your setup, pickups and amp and all, you find the 500K vol/tone pots give you too much edge too much of something you don't want, yep you could stick with some better made CTS pots and add a parallel resistor to either the volume or tone pots to tweak the pickup loading to get the equivalent of your former setup.

I mentioned in my last tirade how RICH has at least one guitar, think it is an Explorer, with a 500T, 1 Meg volume pot, and no tone pot, maxed out pedal to the metal. That sucker outta bark. When he mentioned doing that I asked if had maybe misplaced his power paint stripper and thought he would try a sonic substitute. ;-)

Les Paul Forum Member
My '83 came factory with 500K volume and 100K tone pots. Sometime in the mid eighties I replaced the tone pots with what was available from Gibson at the time. I don't remember what value I was after, but my tones read in the 350K range, one a 338 and the one at the bridge that went bad a 388. They seem to be very good pots though, very smooth travel, brass threaded shafts and quite a bit heavier than the newer CTS. My p/ups are a '59 Duncan in the bridge at 8.2, and the stock Gibson 'PAF' in the neck at 7.7. The Gibson p/ups originally had little stickers on the mounting rings that read 'PAF'. yeah right. Anyway I think I will try the 1M resistor across the 500k tone pot outer lug and wiper. Did I read the math correctly, 1M with 500K = 333K? This has been a very enlightening thread , and BGWN's info as always has provided much insight. Mucho thanks.

BGWN
Glad I could help, good stuff. If you still have the original pots, they are likely CTS made. Look for the seven digit source-date code, if from 1983 the code would likely be 13783xx with the xx's indicating the week within 1983 that the pots were produced by CTS. There seemed to be a whole lot of weird and not so wonderful pots and pickups stuff happening at Gibson back in the earlier Nashville years, the very later 1970s through the mid later 1980s, until the new era management took over.

Les Paul Forum Member
Last night I slapped that 1 meg CTS pot in the R9 for the bridge pu (500T) and it's perfectly bright and chimy now. The taper is also far better for the 500T than the Classic Plus (with Alnico 5 mag) it replaced, so volume swells are much smoother. I was thinking of putting the Classic Plus back in but no need for that now. The 1 meg was originally in the Lucille for the neck position but the taper was all wrong for it as the neck pu is a Duncan 59 neck model. I yanked it, put in a CTS 500k and it's just fine. While I was at it, I put in a push/ pull to disconnect the tone. The difference is subtle as these pickups are of the traditional/vintage variety in terms of output, but it definitely adds a bit more sting to the bridge/neck and neck/middle (I had Lucille routed for a middle pickup). Anyway, thanks for the wealth of advice for us all.