using a blend knob with 2 capacitors?

[Tallwood13]

I'm sure it's been done a million times but I can't find a diagram on it so I figure you guys can help me out. Pretty much I want to be able to go between two different types of capacitors for different tones or at least offer something special on a pickguard I plan to wire up for a project guitar.

I could use say for example a push pull or splurge and buy a varitone but it's more the less a better understanding of what blend does. I know 0 = 100% of one say for example bass pickup and 0% = 100% of the other pickup but how this would work with tone capacitors today interested me in the subject.

Anyways let me know what you guys think

[ItsaBass]

Re: using a blend knob with 2 capacitors?

It would work, but you would have to dedicate an entire pot to it. That is, it couldn't operate as a standard tone control as well. It would be a separate pot that either: 1) selected the capacitance value that a standard, separate tone control used, or 2) selected a capacitance value that affected the entire output signal.

To make it make some sort of sense, you'd probably prefer a blend pot that has a center detente. Capacitors in parallel have their values added. So, one side of the pot's sweep (0) would have the value of the cap you wired onto that side of the pot. The other side (10) would have the value of your other cap. The middle (5 on a linear taper pot) would have the capacitance of both caps added together. As you can see, that's kind of confusing, so I think the center detente would help to clarify it a bit in ones mind.

I did the same sort of thing on my most recent Esquire build, but I used a Gibson-style 3-way switch instead of a blend pot. I have a .0011 uF cap on one side, and a .0022 cap on the other. In the middle position (where I normally leave it), I get a theoretical .0033 uF. (I have not measured the actual capacitance values of those caps.) It's three slightly different sounds from which to choose when in the front switch position.

[jon the art guy]

Re: using a blend knob with 2 capacitors?

I could have sworn I've seen a PCB for this at a guitar electronics site. I'll link out tomorrow when I get up.

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[Tallwood13]

Re: using a blend knob with 2 capacitors?

I could have sworn I've seen a PCB for this at a guitar electronics site. I'll link out tomorrow when I get up.

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thanks that is appreciated. If anything I'll have a better understanding of the blending pot. I figure i'd experiment with other things such as diodes for an "underdrive" effect tonefiend talked about but we'll see.

[jon the art guy]

Re: using a blend knob with 2 capacitors?

thanks that is appreciated. If anything I'll have a better understanding of the blending pot. I figure i'd experiment with other things such as diodes for an "underdrive" effect tonefiend talked about but we'll see.

I have failed. Sorry. The PCB I remember is this:

http://www.guitarelectronics.com/product/PMT-VTREB/

It's a treble bleed circuit for volume.

Itsabass's idea is the best I can think of for the situation though. If you're making a 4 pot guitar, there's plenty of ways to economize controls to suit. I'm going to probably be doing a Master vol/Master tone/ two spin-splits on an Epiphone pretty soon. If you had 4 pots, two masters, a varitone and a tone blend knob maybe?

The link I provided is a pretty good place to pick up oddball pots with detents, push pulls, etc.

[Liko]

Re: using a blend knob with 2 capacitors?

One other idea, similar to the Varitone but with a fully variable blend, would be a variable or trimmable capacitor. They're like a potentiometer, but adjusting them varies capacitance, not resistance. I'd love to play around with one of these, but the trick's been finding the right size (about the same as a standard guitar pot) and capacitance range; most of what I've seen has been in the low picofarad range, for building tunable band-pass circuits for radios. For audio tone circuits, you need one in the 10-50 nanofarad range.