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Thread: 1 meg pots

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    Ultimate Tone Member Natman's Avatar
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    Default 1 meg pots

    Hi all, I wanted to get an idea for how useful 1 meg pots are for adding (retaining) highs on dark pickups. Do you use them? Do they add output? Are they more noisy? Thanks

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    Showmasterologist Robert Delahunt's Avatar
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    Default Re: 1 meg pots

    Reprinted from Seymour Duncan's Tech Tips

    Quote Originally Posted by Seymour Duncan
    We often get calls from people asking what value of potentiometer that they should be using for the volume controls on their guitars. As a general rule of thumb, for single coil pickups we recommend 250k audio taper pots, and for humbuckers we generally recommend 500k audio taper pots. The most basic reason for these recommendations is that it allows a smooth swell in volume from zero to full out. The purpose of this article is to show you what effect changing the value of the pot can have on your pickup's tone. Let's start with the pickup itself: a single coil pickup like our SSL-1 Vintage for Stratocaster. The SSL-1 has a DC Resistance of approximately 6.5k and a resonant peak (the pickup's voice, or sweet spot) of about 10kHz. The characteristic of an SSL-1 (and other single coil pickups) is such that when a note is plucked, the tendency is for the tonal spectrum to leap towards the peak frequency, giving that characteristic "sparkle" in the attack. The amount of "sparkle" can range from minor to overkill depending on what value of potentiometer you use to "load" the pickup's circuit with. In figure 1 you can see the peak characteristics of an SSL-1 with different values of volume pots attached to it. The top curve indicates virtually no load, the second curve down indicates a 1meg pot, the third down is a 500k pot, the fourth is a 250k pot and the bottom curve represents a 100k pot. As you can see, the peak doesn't shift in frequency, but it does shift in amplitude. The difference between a no load state and the load induced by a 100k pot is 19dB (a significant difference)! In figure 2, we show the same settings as they relate to one of our SH-8b Invader™ pickups. You'll notice that in a high output pickup, the difference is not as great. As you reduce the amplitude of a pickup's peak frequency, the surrounding frequencies come into play more and more. This can give a more pleasing balance of frequencies, and is part of the reason for the guitar manufacturer's selection of the volume control's value. What does this mean to you? It means that if you like a pickup's basic character (its peak), you can further shape the tone by increasing or decreasing value of the pot in your guitar. Have fun in your tonal quests!

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    Ultimate Tone Member Natman's Avatar
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    Default Re: 1 meg pots

    Awesome -that's very helpful! FWIW, I have 2 soapbars wound to 12k neck and 18k bridge (I know!) and I wanted to see if I could keep the response of something like a vintage wind by retaining as much highs as I can. Even 2 meg pots are a possibility. I am aiming for really big output without mud.

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    Showmasterologist Robert Delahunt's Avatar
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    Default Re: 1 meg pots

    Quote Originally Posted by Natman View Post
    Awesome -that's very helpful! FWIW, I have 2 soapbars wound to 12k neck and 18k bridge (I know!) and I wanted to see if I could keep the response of something like a vintage wind by retaining as much highs as I can. Even 2 meg pots are a possibility. I am aiming for really big output without mud.
    Well it depends on the amp and other things. I wouldn't go above 1 Meg. Why are you changing pots? Do you need to reduce the amount of bass or highs or something?
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    Ultimate Tone Member Natman's Avatar
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    Default Re: 1 meg pots

    The guitar they're meant for isn't done yet, but I'm anticipating a lack of highs. I could go buy new soapbars, but I already have these so I figured I would try to make them work. There's alot of wire on these bobbins!

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    Default Re: 1 meg pots

    Quote Originally Posted by Natman View Post
    The guitar they're meant for isn't done yet, but I'm anticipating a lack of highs. I could go buy new soapbars, but I already have these so I figured I would try to make them work. There's alot of wire on these bobbins!
    You're anticipating a lot of highs? Well sometimes people use 250k pots to reduce the highs, so I guess you could try 1 meg to increase them, but in reality it's our perception of highs because pots determine the amplitude, not really the frequency.

    You could EQ the amp for the guitar....
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    Default Re: 1 meg pots

    From personal experience, the 1000K pots gave me a brighter and "hi-fi" sound in a bad way (shrill). I don't remember the 1000K pots adding more output or generating more noise.

    I prefer changing caps instead of pots. The lower value caps (.015uf) provide a more organic sparkle sound than the 1000K pots.

    This is what sounds best to my ears

    For paf-level humbucker - I like 500K pots with .015uf cap in the neck, .022uf cap in the bridge.

    For old Fender Widerange (not the reissue crap) - I like 1000K pots with .015 cap

    Anyway, switching caps and pots are easy and inexpensive. I say go for it and report back with your findings.

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    Ultimate Tone Slacker MattPete's Avatar
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    Default Re: 1 meg pots

    A change in caps won't do squat with the tone pot wide open.
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    Default Re: 1 meg pots

    Quote Originally Posted by MattPete View Post
    A change in caps won't do squat with the tone pot wide open.
    This might be true in theory, but I posted under the assumption that adjustment knobs on guitars are there for one reason - to be adjusted!
    Last edited by Kokopelli; 07-19-2007 at 11:59 AM.

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    Default Re: 1 meg pots

    Quote Originally Posted by MattPete View Post
    A change in caps won't do squat with the tone pot wide open.
    Quote Originally Posted by Kokopelli View Post
    This might be true in theory, but I posted under the assumption that adjustment knobs on guitars are there for one reason - to be adjusted!
    Yep. I remember before I started using them, people said my tone sucked but my treble response was excellent. Now I use them and they like my tone.

    Still, again, I agree: the tone pots are there to be used. Now if you prefer the sound of the tone pot not even wired in, get some fender no load tone pots (they have a detent that if you roll them to 10, you go over the detent and the tone knob is literally off). Still, they're useful: never know when you need to play some Slash / "Woman Tone" type stuff. It's all preference.
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    Default Re: 1 meg pots

    You don't necessarily need to use the 1 meg on the volume you can use it on the tone instead. I have used 1 meg for tone because it opens up the frequency range with dark pickups and guitars. I did it with a Dimarzio Megadrive on a swamp ash body. A good rule of thumb is if you are increasing the pot also double the capacitor rating to keep the same tonal curve. So if you change from a 250k pot with a .022 capacitor, go to a 500k pot on a .045 capacitor to keep the same tonal range.
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    Default Re: 1 meg pots

    TR and Koko, good advice.

    MattPete, it will make a difference, but most people haven't trained their ears to hear it. (And frankly, I don't blame them!)

    idsnowdog has the best idea, assuming you use "modern wiring". However, the cap value and the pot value do not interact as he expects in his "rule of thumb". As TR noted, the pot value changes the amplitude only, and has virtually no effect on the frequency. It's a Zobel filter, not an RC filter.

    I have a "resonance control" on one of my guitars. It changes the value of the volume pot from 500K to 1,000K (1 M). JB in the bridge and Phat Cat in the neck. I was hoping to increase pinch harmonics on leads, smooth things out for rhythm. Yes, it's slightly... ever so slightly... brighter on 1 Meg than 500K but it's not worth taking up a hole in the guitar. It's not "icepicky", however, with those winds, despite it being a very bright guitar. YMMV, of course.

    One problem with high resonant peaks is you need a really clean pick attack to avoid sounding like Joni Mitchell. The other downside of 1 Meg pots is they will cause more treble rolloff when turned down, simply because 10% of 1 M is twice 10% of 500K, so you have a resistor of twice the size in line with the cable capacitance.

    Myself, I'd start with 500K pots and .015 caps. Obviously, you need to put them in to finish the guitar. But I'd be prepared to do some experimenting and change things.

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    Default Re: 1 meg pots

    let's be practical :
    start with standard recommended pot and cap values, then go from there

    to be more specific, you could tell us what body, pickups, control scheme you're planning

    you're likely to get what you want with 500K pot and a lower value cap (if necessary)

    the good news is that pots are $5, and caps are $1.
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    Default Re: 1 meg pots

    Quote Originally Posted by MattPete View Post
    A change in caps won't do squat with the tone pot wide open.
    Not true. The cap still bleeds off some treble even on 10. Less so on a 1 meg vs. 500k vs. in turn 250k, but it still bleeds. The only way to "stop the bleeding" is to cut the cap off the volume pot lug.
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