2 meg pot for les paul?

[lowell]

I modded my lp w 1meg linear pots, a 270k across middle and ground lugs, and a 220pf cap across top and middle.

It works great now with my overdrive channel. It's far easier to turn down my volume and clean up the sound. Only drawback is that with the volume all the way up there's still only <270k load on the pickups.

Ideally i'd use a 2meg linear pot with a 470k resistor...just can't find any long shaft 2megs for the job. If I have no luck here I may take the pot apart and increase its value by scratching some of the element off.

[David Schwab]

If you have a 270K resistor, then it's not really a 1 Meg pot anymore. The problem with using large value pots like that is when it's on 10, you have less load on the pickups. But when you turn it half way down, you have more load on the pickup than you would with a 500K pot. The reason for this is the potentiometer works like a voltage divider. On 10, you have zero resistance between the pickup and the amp, and 1M to ground. When you turn it half way down, you now have 500K between the pickup and the amp, and 500K to ground.

On a 500K pot you would have less series resistance. So the 1M pot can get muddier when you turn it down.

So with your use a resistor, you are still loading the pickups more than with a 500K pot on full, and when you turn it down you have more series resistance. The reason it doesn't sound muddy is the cap.

I would just use 500K pots with a 220pF cap. I like to use a 180pF cap.

[lowell]

David,
Yes I am aware of the above conditions. I did this because I use an overdrive amp and 500k audio pots just don't cut it... they don't have the right logarithm, which I believe would be 30%. With 500k audio pots the volume doesn't reduce until around 1.5 on the control knob. This is tough because Les Pauls need the long shaft pots which limits my choices.

As of now I have the 1 megs in there and it's definitely better on the overdrive channel. I also have a 220pf bright cap.

[David Schwab]

I prefer linear taper pots for volume controls. Give them a try.

[pdf64]

'With 500k audio pots the volume doesn't reduce until around 1.5 on the control knob'

That seems more like a linear taper, ie when used with overdrive, a linear taper guitar vol control only has much effect in the 0-10% rotation range.
With a clean system, linear works best, especially if balancing pickups to each other.
As the system gets more overdriven, an audio type taper is needed.
As a guide, I suggest you try 20 or 30% taper for hot country gain levels, 10% for heavy rock.
Weber sell 20% taper pots.
Most other audio taper pots are 10% taper, eg CTS.
I also can't follow your rationale for 1M pots - most likely there was a taper problem with the 500k pots you tried.

[lowell]

My rationale for the 1M pots:

If you have a linear pot that you want to make a specific LOG taper, as I'm sure you already know, you place a resistor across the ground and center terminal. I know that a parallel resistor of about 1/4th to 1/5th the value of the pot will achieve this. However in the case of impedance I do not want to put a 500k pot w/ a 150k Rp on it - too much loading of the pickup. When the volume is all the way up it'll be <150k. So I chose the 1meg/270k combo. I also have a Cp of 220pf from top to center terminals.

I'll look into the Weber pots. Why do you suggest 30% for country and 10% for heavy rock? I'd think Heavy rock would have more gain thus requiring a high taper%.

[lowell]

I just had a thought. Why not use a 500k REVERSE log? If the volume turns down at 1.5 on the control with a regular audio pot, then it'd be 8.5 w/ reverse right? I can then fine tune it w/ a Rp from the top to center lugs, AND not mess w/ impedance when the pot is on 10. Maybe I'm way off here.

1 more Q:
What % taper is a 1meg with a 270k Rp from center to ground?

[David Schwab]

AND not mess w/ impedance when the pot is on 10.

As I pointed out, with a 1 meg pot you have MORE loading when you turn the pot down than when you turn down a 500K pot, but less when it's on 10.

[David Schwab]

'With 500k audio pots the volume doesn't reduce until around 1.5 on the control knob'

That seems more like a linear taper, ie when used with overdrive, a linear taper guitar vol control only has much effect in the 0-10% rotation range.

No, thats audio taper. It's slow until you get to the last 10%. it has nothing to do with overdrive. With linear, when you turn the know half way, you have reduce your level by half. Audio taper is only needed for doing smooth fades. And even then, many mixers use linear. When they use audio taper faders you can see the numbers getting closer together as you approach 10.

Look at the log taper on this chart. And notice that most log (audio) taper pots aren't really log taper, but a composite of two linear tapers (commercial log).



Some good tricks here:

Potentiometers (Beginners' Guide to Pots)

[lowell]

The pickups are connected to the top of the pot, so in general, stock wiring, the pickup loading doesn't change throughout the pot's rotation. (ignoring the input impedance of the pedal or amplifier)

It does change when a resistor is added in parallel.

Maybe we're saying the same thing in different words. ?

[David Schwab]

The pickups are connected to the top of the pot, so in general, stock wiring, the pickup loading doesn't change throughout the pot's rotation.

Yes it does, that's why you lose highs when you turn down the volume.

(ignoring the input impedance of the pedal or amplifier)
It does change when a resistor is added in parallel.

It also changes when you have a resistor in series. You have to look at it this way; when the pot is on 10, you have 1M between the pickup and ground, and zero ohms between the pickup and amp. Now let's assume it's a linear pot, since that's easier to deal with for this example. If you turn the pot half way down, you now have 500K between the pickup and ground; more loading, and you have 500K between the pickup and the amp. That also increasing the impedance. The PRS Santana models use series resistance to darken up the tone. You can also add a resistor between the pickup's common end and ground, and that will also dull the tone.

What you will find with 1M pots is they are brighter on 10, but get duller than 500K pots when you turn them down. Of course a treble bleed cap more-or-less fixes it.

I feel your pain though. I had been doing similar things with blend pots on basses because I didn't like the taper. All the blending action was around the first 5-10% of the rotation from center.

Just keep trying things, or maybe different brand pots.

[Chuck H]

No disrespect to what anyone is saying is intended.

I don't see any problem with what lowell is doing. So what if the series resistance is higher when the pot is being turned down. That's why he's turning the pot down. He wants to reduce signal. The "bright" cap is there so the tone won't become muddy. If lowell wants to experiment with wierd pot/component arrangements and he's aware of the final loading effect of the ground resistance I don't think it's a bad thing at all. However I do side the other posters in that this method is sort of unruly and difficult to fine tune. I also think lowell simply hasn't tried the right pot yet.

I play high gain and do use my volume control. The smaller the taper % on a log pot the slower the adjustment. So if you want maximum adjustment controling high gain you need a small taper % log pot. I'm using a 30% taper now and I only have clean tones up to 1 on the volume control. I'm use to it so I haven't troubled to change it out. But a 10% taper would allow me to get to around 3 before I run out of "clean". A wider comfort zone to land in when I'm twisting on the knob. So lowell, just in case you haven't tried the right taper yet maybe go ahead and try a 500k 10% taper pot and see if it does what you want. This would be much simpler than what your doing now and it should work fine.

For high gain the "bright" circuit across the top and ctr of my guitar volume control is a little different from what most people use. I have a 150k resistor in series with a 220pf cap. Trust me. If you are using a high clipping content give this a try.

HTH

Chuck

EDIT: I am using a frankenstrat with a humbucker in the bridge and I switch to my singles for clean tones. But I have used the same rig with a 'Paul with stock pots and though it's a little more touchy you can get clean with the two pickups in parallel.

EDIT2: Mouser carries Bourns "guitar" pots. They are 10% taper pots with shaft options. They are full size pots (not 16mm) so I don't know if they will fit in your LP control cavity.

[lowell]

David,
Technically there is still the full pot value between the pickup and ground, regardless of where the center lug sits. It's my understanding that the series resistance when the pot is turned down is what creates the high-end rolloff. Doesn't this series resistance increase the Zout, interacting with the Zin of the amplifier thus rolling off highs?

[David Schwab]

David,
Technically there is still the full pot value between the pickup and ground, regardless of where the center lug sits. It's my understanding that the series resistance when the pot is turned down is what creates the high-end rolloff. Doesn't this series resistance increase the Zout, interacting with the Zin of the amplifier thus rolling off highs?

Yes, that's right. There's two ways to wire up a volume control, the Les Paul way, and the Jazz bass way. I mostly do the Jazz bass way so turning down one doesn't cut off both pickups.

But either way you are increasing the impedance and you lose high end. And even wired up like the Gibson way you lose high end. You lose more high end with a 1Meg pot when it's turned down because of the series resistance. You are talking about a passive volume control. You really can't separate the input impedance from the output impedance. It's all interrelated. So is the capacitance of your patch cord.

The only way to get a nice even volume sweep and not lose tone is with an active buffer.

[David Schwab]

No disrespect to what anyone is saying is intended.

I don't see any problem with what lowell is doing. So what if the series resistance is higher when the pot is being turned down. That's why he's turning the pot down. He wants to reduce signal. The "bright" cap is there so the tone won't become muddy. If lowell wants to experiment with wierd pot/component arrangements and he's aware of the final loading effect of the ground resistance I don't think it's a bad thing at all. However I do side the other posters in that this method is sort of unruly and difficult to fine tune. I also think lowell simply hasn't tried the right pot yet.

Right, I said in my last post "Just keep trying things, or maybe different brand pots." I've done all this before and used to use 1 and 2 Meg pots.

A wider comfort zone to land in when I'm twisting on the knob. So lowell, just in case you haven't tried the right taper yet maybe go ahead and try a 500k 10% taper pot and see if it does what you want. This would be much simpler than what your doing now and it should work fine.

Which is what I was saying....

For high gain the "bright" circuit across the top and ctr of my guitar volume control is a little different from what most people use. I have a 150k resistor in series with a 220pf cap. Trust me. If you are using a high clipping content give this a try.

I do it without the resistor usually, but both work well. depends on how bright you want it. PRS also doesn't use the resistor.. not that I care for PRS guitars, but I noticed that one day.

EDIT2: Mouser carries Bourns "guitar" pots. They are 10% taper pots with shaft options. They are full size pots (not 16mm) so I don't know if they will fit in your LP control cavity.

Those are very nice pots. I just started carrying all the Bourns stuff. The blend pots are really good also. I just wish they had metric solid posts so I could use them with Hipshot knobs.

I don't see why full size pots wouldn't fit into a LP. That's what they always used.