Tweaking either a 1 meg pot to a 500k and a 500k to 250k
and
3 very common treble bleed modifications

by John Spina

Purpose of this Tutorial
Let's say you need a 500k pot for a project but you only have a 1 meg pot? What do you do?
It's Sunday and no one is open.. ;o)
Ok...What if you actually have a 500k pot but now you want to try a 250k value instead?
I'll show you how to very easily remedy these questions.
Notice the first picture shows a 500k CTS audio pot that reads almost perfectly 500k (This is getting pretty rare these days!) The meter shows .501 which is 501k actually. The second picture shows a 1 meg pot and notice it reads 1.095 which is a little over 1 meg.
We are going to change this 1 meg pot to be used as a 500k pot by placing the correct value resistor across both outside terminals of the 1 meg pot. In this case as you see in pictures above, that we would use a 1 meg resistor.
 
The picture to the right shows proper placement of the 1 meg resistor. I'm showing a 1/4 watt resistor which is fine or you can use a 1/2 watt but the 1/2 watt will take up a bit more room. When you solder the resistor onto the pot legs, be sure to use a heat sink and also try to place the resistor in such a way that it gives you plenty of room to solder your wires onto the terminals. I like to wrap the resistor wires below the terminal holes and at the bottom of the terminals so I still have plenty of area left within the terminal holes to solder my wires to.
Now that the the 1 meg resistor has been soldered across the 1 meg pot, we now have a reading of .524 or 524k. A pot must be within + or - of 20% and it is within those tolerances. If you wanted to get this reading exactly 500k or very close, you would have to mess with the resistor value you placed across the pot. The higher this resistance value, the more highs the pickups and the overall circuit will see. The lower this resistance, the less highs and the fuller or fatter the tone becomes. A Strat uses 250k for a beefer bright tone but 500k pots in a Strat are too bright and harsh to my ears with single coil pickups. But anything goes!
OK now onto bringing the 500k pot value down to 250k. I first tried using a 470k resistor but it brought the pot down to around 240k. I want at least 250k or higher on my pot. I always want the rated value of a pot or higher. If the pot reads high, I can knock it down some with a resistor, but if it reads too low, I can't do much of anything with it? The picture above to the left shows the 470k across a CTS 500K pot. The picture above to the right shows a reading of only 241k with the 470k resistor.
 
Next I tried using a 750k resistor across the 500k pot. The 750k resistor gives us a very versatile 300k reading. This is a good reading for the guy that has a Strat with a full sized bridge Humbucker and 2 vintage single coils in the neck and middle positions. The Humbucker likes to see the 500k value, but the single coils work better with 250k. 300k is a great middle of the road value for compromise overall in this scenario. These values can be tweaked until you find something that is perfect for your ears. 350k, 400k etc. just by tweaking these resistor values.
Notice the 750k resistor to the right gives us exactly 300k. This value was also used on a lot of later Gibson axes, but stick with 500k in your Gibsons... ;o)
The picture to the right shows me using two 1/4 watt 1 meg resistors in parallel. Resistors in parallel give you have the reading of both resistors together. Resistors in series doubles these values. Notice the pair of 1 meg resistors in parallel is giving us a 500k value.
This shows the 1 meg resistors in parallel placed across both outside legs of the 500k CTS pot and we now have a perfect reading of 250k on our original 500k pot. It only cost's a few pennies for some resistors you can get from Radio Shack. Putting a resistor across the pot and lowering the values does change the taper a bit. The taper is close but the resistor seems to slow the taper or make the taper more gradual than without the resistor. I don't find this as too much of a problem and if it drives me nuts, I'll get the actual value needed.. ;o)
Here are some useful readings I got during the creation of this info...This was with the 500k pot..
500K pot...220k and 330k in series gave me 263k
500k pot...330k and 330k in series gave me 286k
500k pot...220k and 220k in series gave me 233k
500k pot....1 meg and 1 meg in parallel gave me exactly 250k
Let's Talk About Treble Bleed Mods And The 3 Types I'm Showing
Purpose of the Treble Bleed Mods....To retain high end as you roll your volume control towards 0. This retains high end clarity and avoids the dark muddy tones. The volume and tone thins out naturally while you roll off volume but the highs and clarity stay...
 
The Picture to the right shows a resistor and cap value in series (top of picture is the Kinman mod) and parallel (bottom of the picture is the Duncan Mod). The reason for having a resistor with the cap is as follows. The cap itself controls how much of the guitar's circuit puts highs to ground. The cap value also changes the frequencies to a small extent. Smaller caps allow more highs to remain in the circuit but makes the tone thinner as you roll off volume. If the cap value is too high, then as you roll down volume, you actually have a brighter tone lower on the volume than you did with the volume on 10.
The trick is to use whatever cap value is transparent. My favorite values are 680pf, 820pf and .001 or 1000pf. I use these values in my Humbucker guitars with 500k pots. In my Strat's I Like using either Kinman's mod of using a 130k resistor in series with a .0012 cap or Seymour Duncan's mod of using a 100k resistor in parallel with a .002 cap. Lately I prefer the Duncan mod more. The resistor with the cap controls how fast the cap is allowed to either send or not send highs to ground. To some extent, the resistor also changes the pot taper and it's resistance? Not sure on this as I've not done a lot of research on it, I'm also told that the series components have less effect on the taper of the pot and that the series resistor is a more gradual effect on the cap. You'll have to let your ears decide on this one. Both mods work great and are transparent though.
This Picture shows the correct placement of the parallel components of 100k resistor and the .002 cap. Notice you'll always place the components on the 2 terminals away from the terminal that is grounded to the pot case for it to work.
This picture shows the Kinman mod of putting a .0012 cap in series with a 130k resistor. Both of these mods are for 250k pot values. Make your connections tight and neat and use a heat sink while soldering and heat shrink tubing anywhere you feel you might have components touching places. I have the components placed purposely so you can see where they mount on the pot.
This picture is probably the most popular treble bleed mod and was used on older Telecasters to retain high end and over all bright snappy Tele tones. The Tele had a .001 across it's volume control. Some Tele's actually used a 1 meg pot also. We are talking bright. On my Les Paul with Duncan Humbuckers in both neck and bridge positions I have found I like just a ceramic 820pf cap across the bridge volume control and a .001(1000pf) across the neck volume control. I Like .015 mfd caps across my tone pots and I use CTS 500K pots. I Only use this treble bleed mod on my 500k dual Humbucker Gibson guitars.
You can see how with a few simple and overlooked mods, that you can really tweak your guitar around. You can tweak your tone for brighter, darker, and less mud while you volume down using these easy ideas. Enjoy!

 

 


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