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Creating a "blend switch"? A rotary switch that acts like a stepped blend?

Discussion in 'Pickups & Electronics [BG]' started by fourstringbliss, Feb 25, 2014.

  1. fourstringbliss

    fourstringbliss Supporting Member

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    I have a blend knob on my bass, but to my ears they always sound like a switch. I don't hear a real difference at the in between settings, so it's either neck, middle, or bridge. I was debating replacing it with an actual switch when a fellow TB'er suggested a "blend switch".

    Here's what he suggested:

    There is another option. A blend switch. I've wired these several times for myself and for customers. A 2 pole, 5 or 6 throw rotary switch is ideal. Typically you'd have it arranged like a blend control with bridge solo, then clockwise through 3 or 4 different blends and then neck solo. It works much like an MN blend with the earth lifted, but of course there's no tweaking, you just switch straight to the blend you want. You can even have trim pots instead of fixed resistors.

    But I've also had a few variations on this. My favourite, in a customer's warwick thumb years ago, was a 3 pole, 4 throw switch that had resistors to set two favourite blends, neck pickup solo, then both on full with no resistors. She could flick straight to four nice usable different sounds that were all the same volume.


    I PM'd him about it and haven't gotten a response (no problem, people are busy), so I put it to you - how would I do this?

    I ordered a two pole, six position rotary switch. I figure pole one will be neck and two will be bridge. Position one will be neck only, three will be both, and six will be bridge only, with wires running from those lugs to a single one that will go to the volume.

    What about the other positions? How do I wire resistors to simulate 100% neck with 75% or 50% bridge, etc.? I don't know that much about how resistors work. What value of resistors do I need?

    Thanks for any help you can give me!
  2. BlueTalon

    BlueTalon Happy cynic Supporting Member

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    Disclosures:
    Endorsing Artist: Turnstyle Switch
    My first suggestion would be to edit your post so that the quoted portion is not yellow font. That is impossible to read.

    Regarding the rest of your post, it sounds like a good idea. Superior IMO to a regular pickup selector switch.
  3. fourstringbliss

    fourstringbliss Supporting Member

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    Doh! My screen has blue, so the lettering shows up yellow. It wouldn't show up on a white screen... :rollno:

    Is that better?
  4. ngh

    ngh

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    i'm gonna give this a bump because i would like to do this too
  5. line6man

    line6man

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    I got your PM, but haven't had a chance to respond until now.

    This concept comes up every now and then, and I've done a few diagrams for it. Here is one for a six position switch, with a master volume and tone. If you intend for some positions to be "all or nothing," use shunts, rather than unused trimmer pots.
    [​IMG]

    The problem is the concern for practicality. It can be difficult for some players to pick the right settings for the various presets to be usable in all playing situations. Between that, and the complexity of wiring many trimmer pots, it's rather uncommon to see this.
  6. fourstringbliss

    fourstringbliss Supporting Member

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    Thanks for responding!

    Can it be done without the trimmer pots? I'm really just looking for a few settings between full neck, both, and full bridge. How would I do this just using resistors? How could I simulate in between blend settings with fixed resistors?
  7. line6man

    line6man

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    You can use resistors, but it will be tough to choose values.

    FWIW, it might be best to only use one resistor per pickup, per position. There is no need to have resistors to ground, since you can use the switch to solo the pickups when you need it, so you just need resistors between the pickups and the output. Additionally, without resistance to ground, you will only need two poles of switching, rather than four.
  8. walterw

    walterw Supportive Fender Gold Supporting Member

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    trouble is you'd need the trimmer pots to find just where that "sweet spot" is before replacing them with equivalent resistors!

    what you're trying to do is find the resistor value that gets you that sound where one pickup just begins to change from being "loaded" by the other pickup being brought in.

    a jazz really only has 5 sounds (skipping the tone knob): neck, neck loaded by the bridge, both, bridge loaded by the neck (all-important), and bridge.

    i tried this a while ago, with a 3-way rotary dialed in with resistors for the middle three, "mostly neck/both pickups full/mostly bridge"; it seemed like the magic spot for the blend changed depending on what the bass was plugged into, due to different impedances or whatever.

    ultimately, a blend pot just works better.
  9. fourstringbliss

    fourstringbliss Supporting Member

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    The rotary switch that I bought has two poles and six positions. The pickups are humbuckers and I have them connected to a 500k volume and 500k blend. What resistor values would you suggest for simulate pickup blending between full on settings? How would you wire them?
  10. fourstringbliss

    fourstringbliss Supporting Member

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    So, would I be looking at something like this?

    [​IMG]

    All the way forward is just neck. 2nd position is full neck and bridge through a resistor. 3rd position is full neck and bridge. Positions 4 and 5 would be full bridge and neck through resistors. 6th position would be just bridge. all leads connect to one wire that would go to the volume pot.
  11. RobbieK

    RobbieK

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    Sorry mate, yeah I've been away.

    [​IMG]

    OK, this is the sort of thing I had in mind. The switch is drawn as a rotary switch viewed from the bottom. So full anti-clockwise has the bridge solo, in the third position, both coils on full, and fully clockwise is the neck pickup solo. IOW, positions 1,3 and 5 are just as a normal three-way pickup selector switch is.

    As you can see, positions 2 and 4 have one coil on full plus the other coil summed through a series resistor. This is pretty much how an mn blend pot (with the earth not connected) works.

    To choose resistors, either temporarily wire an mn pot, find the blend you like, then disconnect and measure with a multimeter. Or temp wire a 100k linear pot instead of the resistor and tweak till it floats your boat, then disconnect, measure.

    I just noticed you've bought a 6 pos switch. No matter, the concept is obviously adaptable for the extra position. You just have to choose another blend and measure...
  12. JustForSport

    JustForSport

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    Maybe a different (resistance) value blend pot will work better.
    A volume pot that is the wrong value for the setup will act more like a switch than a gradual taper.
    Maybe someone here can suggest a better one if more is known about your bass- types of pickups, existing pot values, etc.
  13. fourstringbliss

    fourstringbliss Supporting Member

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    Excellent! Super easy switch to put together. I might search around for a 5 position switch, but all the 5 position switches I could find were all 4 pole and I'm concerned they might not fit in my control cavity. I might just leave the 6th position empty for a kill switch setting.

    I'm using a 500k blend as it is, so 50% blend would theoretically be 250k, right? Maybe a 100k resistor would be that place where one pickup is just starting to be loaded by the other pickup coming in? I could try and fiddle with a pot to find the "right spot" but that sound is going to change depending on what I plug my bass into. I might just get a couple of 100k, 150k, 200k, and 250k resistors and plug-n-play to find the right ones. I could wire up the switch except for the resistors and then hook a pair of resistors in to see how they sound.
  14. Jazz Ad

    Jazz Ad Mi la ré sol Gold Supporting Member

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    I don't understand how this would be more practical than a regular blend or a simple 3 position switch if it's your thing.
  15. fourstringbliss

    fourstringbliss Supporting Member

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    A blend pot always seems to act like a 3-way switch to my ears. I think this might give me 5 easily switchable, predictable sounds, rather than fiddling with a blend. Plus, I can factor in a kill switch on one of the settings.
  16. Wagz

    Wagz

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    One other thing to consider is that most standard 2-pole 6-position switches will disconnect in between positions. This will lead to popping if you move the switch while playing.

    If you're going to "set it and forget it", this won't be a problem.
  17. fourstringbliss

    fourstringbliss Supporting Member

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    The one I ordered is a make-before-break one, so there won't be a pop.
  18. Jazz Ad

    Jazz Ad Mi la ré sol Gold Supporting Member

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    My point being, if you don't head the difference with a blend you won't hear it with a switch.
  19. fourstringbliss

    fourstringbliss Supporting Member

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    Entirely possible. It's not that I don't hear it, I mainly don't like fiddling with it to get a particular sound. The lure of the blend switch for me is being able to quickly switch to particular predictable sounds. The idea of a kill switch aspect is growing on me too.
  20. BruceWane

    BruceWane

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    Before going to all this trouble, you might try ungrounding your blend pot, or replacing it with a "known good thing".

    There's been LOTS of discussion here regarding blend circuits because they often operate just as you describe yours.

    But if you read some of the past discussions here, you'll find that they can work much better - often at no cost (removing grounding from your existing blend pot) or at very low cost (replacing your existing blend pot with a $5.00 Bourns 500K M/N taper blend pot, ungrounded - this is the "known good thing").

    Like I said, lots of threads regarding this, but you can get all the information you need from this thread , and the thread linked within that one.

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