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Thread: Wiring a Rheostat for my guitar

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    Tone Member heem6's Avatar
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    Default Wiring a Rheostat for my guitar

    I had this idea for a new guitar I'm putting together.

    Instead of a selector switch, I would like to wire a potentiometer to "choose" between two humbucking pickups. Dial all the way to the left and it would be the bridge pickup, all the way to the right and it's all the neck pickup. But if it does work, you'd have much more variety in how much or little of each pickup gets put in the mix. I never use the tone control, so it would be wired up to that pot.

    Forum members, can you tell me if this would work, or am I completely out in left field on this one?

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    Ultimate Tone Slacker RW James's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    I was actually considering the same thing. My guitar has two volume pots and two tone pots. I thought of turning one volume into a master volume and the other into a "balance" pot - or perhaps "pan" would be a better term.

    You would probably need a linear pot to make it work.

    The thing that stopped me was the fact that you could never turn them both up all the way. I'm not sure if that is a real problem - but it crossed my mind.
    Rick
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    Ultimate Tone Slacker ParameterMan's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    You want something like this.

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    Ultimate Tone Slacker RW James's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    Quote Originally Posted by ParameterMan View Post
    You want something like this.
    Very nice! That would be perfect.
    Rick
    (the original Rick James!)

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    Ultimate Tone Slacker ParameterMan's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    My plan is to take a dual humbucker guitar with two volume controls, and swap 'em over to master volume and blend. I'm tired of juggling two knobs when trying to change volume and keep the pickup balance the same.

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    CheapGuitarologist ArtieToo's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    Quote Originally Posted by ParameterMan View Post
    My plan is to take a dual humbucker guitar with two volume controls, and swap 'em over to master volume and blend. I'm tired of juggling two knobs when trying to change volume and keep the pickup balance the same.
    Thats fine as long as you understand the consequences of total pickup loading. Lets say you choose the 500k blend pot. Since you won't be using a selector switch, both pups will "see" both pots in parallel all the time. Thats a 250k load to start with. Now, lets say you add a 500k master volume. That drops the total load to 166k.

    That will result in a noticable output and high-end loss. Make sure thats what you want.

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    Tone Member heem6's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    Yeah, this is what I was envisioning!

    If I used a 1mg Pot for the Master Volume, and the 500k Pot for the "Blend," the net effect would be like having a single 500k Volume pot, right? ( There would be no tone control in the circuit. )

    As I believe RW James said, would I be faced with not having either pickup on full at any time? I would hope that having the knob turned all the way in one direction would cancel out one of the pickups and only allow the other to come through.

    Thanks for the link and the information, everyone!

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    Ultimate Tone Slacker RW James's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    Quote Originally Posted by ParameterMan View Post
    You want something like this.
    Quote Originally Posted by ArtieToo View Post
    Thats fine as long as you understand the consequences of total pickup loading. Lets say you choose the 500k blend pot. Since you won't be using a selector switch, both pups will "see" both pots in parallel all the time. Thats a 250k load to start with. Now, lets say you add a 500k master volume. That drops the total load to 166k.

    That will result in a noticable output and high-end loss. Make sure thats what you want.
    I'm just trying to understand how this would work. My thinking would be to have the leads from each pickup connected to each side of the blend pot (linked above) - then output from the blend pot to the master volume. Wouldn't that be in series? Not parallel?

    And as I understand the way the blend pot works, if you are in the middle position, the load is zero. So if the you used 500k pots all the way around, the most you should ever see from one pickup would be 1 meg. But if you were in the middle position, it would only go to 500k.

    Am I missing something here?
    Rick
    (the original Rick James!)

    Sing unto Him a new song; play skillfully with a LOUD noise. Psalm 33:3
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    Tone Member heem6's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    Here's the wiring diagram from Stew-Mac.


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    Ultimate Tone Slacker RW James's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    Isn't that in series?
    Rick
    (the original Rick James!)

    Sing unto Him a new song; play skillfully with a LOUD noise. Psalm 33:3
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    Tone Member heem6's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    I honestly don't know enough about wiring or electronics to tell whether it's series or parallel. Maybe Artie or one of the others can chime in...

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    Ultimate Tone Slacker ParameterMan's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    Quote Originally Posted by ArtieToo View Post
    Thats fine as long as you understand the consequences of total pickup loading. Lets say you choose the 500k blend pot. Since you won't be using a selector switch, both pups will "see" both pots in parallel all the time. Thats a 250k load to start with. Now, lets say you add a 500k master volume. That drops the total load to 166k.

    That will result in a noticeable output and high-end loss. Make sure thats what you want.
    Sure I'd be using a selector. All I want is to stack both volumes on one knob. That way, my neck-to-bridge balance can be the same at any volume level. A blend knob is a lousy replacement for a 3-way switch.

    I can see if I'm using passive pickups I'll probably need a 1k MV. Thanks for pointing that out.

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    Ultimate Tone Slacker ParameterMan's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    Parallel. It's two volume pots strapped back to back and wired opposite of each other. Both pots also cover the whole 500k in half the travel and are full volume from there on out. See my drawing:
    Attached Images Attached Images  

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    CheapGuitarologist ArtieToo's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    Quote Originally Posted by heem6 View Post
    If I used a 1mg Pot for the Master Volume, and the 500k Pot for the "Blend," the net effect would be like having a single 500k Volume pot, right?
    No.

    Quote Originally Posted by RW James View Post
    I'm just trying to understand how this would work. My thinking would be to have the leads from each pickup connected to each side of the blend pot (linked above) - then output from the blend pot to the master volume. Wouldn't that be in series? Not parallel?
    No.

    Quote Originally Posted by RW James View Post
    And as I understand the way the blend pot works, if you are in the middle position, the load is zero. So if the you used 500k pots all the way around, the most you should ever see from one pickup would be 1 meg. But if you were in the middle position, it would only go to 500k.

    Am I missing something here?
    No, yes.

    A blend pot, (rated at 500k), will be two 500k pots in parallel, for a total resistance of 250k. Add another 500k in parallel, (as in a master volume), and you have 166k. Make that master 1 meg instead, and you have 200k.

    Look at this diagram:



    The top shows the blend pot in blue. The bottom shows the same thing, but simplified a bit to make it easier to see that all three pots are in parallel. The rule is: any time you have resistors in parallel, the total resistance is always less than the smallest resistor.

    Think of it like this: lets say you have a 100 ohm resistor. The "100" is a rating of how much current is "resisted", or blocked. If you add another resistor in parallel, you've allowed some current to bypass that electrical dam, thus lowering the total resistance. Some current sneeks by your 100 ohm.

    So . . . a 500k blend pot with a 1 meg master volume will be seen as a constant 200k load. Thats not bad per se, as long as you understand the sonic implications of a 200k load.

    Make sense?

    Artie

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    CheapGuitarologist ArtieToo's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    Look at ParameterMan's drawing. Note, on the right, that even when "A" is taken out of the circuit, "B" is still connected to the top of both resistors. "B" will still "see" the parallel load of two 500k pots, for a total of 250k. Add in the 1 meg master volume, (in parallel), and you have a total of 200k.

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    Tone Member heem6's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    Thanks for all the info, Artie.

    I'm having to rethink this, because I like guitars that run as wide open as possible, and 200k probably isn't what I'm looking for. Is there any other way you can think of wiring this to accomplish the same thing but without throwing the resistance down that low? Maybe someone makes a 1mg blend pot?

    Question - It's clear why the two "stacked" pots comprising the blend pot would read as 250k, but I thought the 1mg pot transferred all of the signal that came into it. Evidently that's not correct. You're saying it will take an additional 50k out out of the signal.

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    Ultimate Tone Slacker RW James's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    I'm sorry, but I still do not understand why this is parallel. To me, parallel is when the path from A to B goes through both resistors simultaneously - series is when they go through sequentially. But I am willing to learn.

    Here are my diagrams as I understand it. First, the standard setup (simplified without tone controls or 3 way switch (assume the switch is set to the middle position)):

    As I see it, when the pots are all the way up, the path bypasses the resistors completely and you have full volume. When the neck pot is up and the bridge pot is down, the bridge resistor has no effect on the neck volume at all. Now even though they are drawn next to each other, electrically they are neither parallel nor series.

    Here is how I understand the blend pot works.

    In the middle position (the blue line) both pickups are full volume since the path doesn't go through any resistors until it gets to the master pot. And if the master pot were all the way up, then that resistor would be bypassed as well.
    In the red position, the bridge pickup would still be full volume, but the neck would be all the way down. Trace the signal from the bridge pickup and you will see it goes through no resistors - however, the neck pickup signal goes through the full resistor of the blend pot.
    Similarly in the green position, the neck pickup should be full volume and the bridge should be full off.

    Now, the master volume pot, looks like it is in series to me - that is, the signal must first go through the blend pot, THEN go through the master pot. Sequentially, NOT simultaneously.

    What am I missing here?

    By the way, this is how Stew-Mac says it works if I understand their little write up.
    Rick
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    Ultimate Tone Slacker ParameterMan's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    You've got it exactly right. What's confusing you is that current always flows through the 500k pots to ground. It would take a much higher value to completely block it- maybe 10M or more, I'm not sure exactly. Maybe Artie would know.

    So in that case, all three pots are shunting signal to ground simultaneously and in parallel.

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    Ultimate Tone Slacker ParameterMan's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    So at this point, my wheels always start turning: you should never need to pan more than 50%, because that would make the selector redundant. Why not add 500k resistors between the pan pots and ground? That should roughly simulate being able to turn a 1M pot halfway. How about even more resistance? I find with two humbuckers the sweet spots are found when the pickups are almost the same level. I never really get the pickup's levels more than two or three points away from each other, and then keep losing that sound when I turn the overall volume up or down, because it's virtually impossible to turn both knobs the exact same amount. So I don't need too much range. How about disconnecting the ground altogether? I'm not sure how much volume drop would result from 500k of pure series resistance, though.

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    Ultimate Tone Slacker RW James's Avatar
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    Default Re: Wiring a Rheostat for my guitar

    Quote Originally Posted by ParameterMan View Post
    So at this point, my wheels always start turning: you should never need to pan more than 50%, because that would make the selector redundant.
    Actually, I was thinking that if I did this, I would change the selector switch to a split coil switch. Center - no split, down - bridge split, up - neck split.

    I'm not really sure I want to do go with the blend pot - I was just thinking of it. It came from the same frustration you had mentioned "juggling two knobs when trying to change volume " which is still a noble cause.
    Rick
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