Two independant volume pots for two pickups. No switch. How can I do it?

[Phil Gerke]

Hey guys,

So I'm stumped on how to wire this up. I want to be able to basically mix the signal of two pickups together using seperate volume controls for each (probably tone controls for each in there as well, tied to corresponding volume pot). Simply wiring them to the same output just does not work as it puts them together in a parallel circuit and everything gets crazy at that point. I think I read somewhere that you can do this with an active setup, but not passive. Does that make sense? It kind of does I suppose, I mean mixers do it.

Is a blend pot my only work around?

To sweeten the deal, one pickup is 250k and the other is 500k. How does that interact when sent to the same blend?

Anyway I'd love to hear some ideas from you all.

Thanks so much!
Phil

[Elias Graves]

Re: Two independant volume pots for two pickups. No switch. How can I do it?

Find a Jazz Bass diagram. That's exactly what you're describing. Two volumes, one tone, no switch.



Just sub the 500k pot where you need it and use the tone cap of your choice. Should work.

[astrozombie]

Re: Two independant volume pots for two pickups. No switch. How can I do it?

I don't think there's a difference between using a 250k pot for one and 500k pot for the other... except that one will sound "darker" and "brighter" respectively.

[Phil Gerke]

Re: Two independant volume pots for two pickups. No switch. How can I do it?

I tried doing basically the Jazz setup and it put everything in parallel including that 250k pot which dulled stuff too much. Honestly I don't understand why the Jbass approach works for the bass but not for my setup. My research is kind of leading me towards needing to use an active circuit to get done what I want. I was entertaining a blend pot, but I'm not sure just yet if I'm okay with that. Its a weird project. I think I have made up my mind to abandon the initial independent volume idea.

[uOpt]

Re: Two independant volume pots for two pickups. No switch. How can I do it?

I mentioned this several time before, so here it goes again.

While some bassists (especially those with two vintage style single coils) can get away with it it usually isn't a good idea for guitars.

To make this work you need to connect the pots backwards, otherwise turning one all the way down would kill both. But if you connect them backwards there is a much increased resistance load on the pickup (much more than a forward connected pot in the same position) and that kills the (amplitude of the) resonance peak. It's fine as long as it is either one pickup only or both full on, but any position in between has this problem.

I'm not saying it must be horrible, but I'm pretty sure that e.g. with two PAFs that would be insatisfactory as they rely on a good resonance peak.

[Phil Gerke]

Re: Two independant volume pots for two pickups. No switch. How can I do it?

I mentioned this several time before, so here it goes again.

While some bassists (especially those with two vintage style single coils) can get away with it it usually isn't a good idea for guitars.

To make this work you need to connect the pots backwards, otherwise turning one all the way down would kill both. But if you connect them backwards there is a much increased resistance load on the pickup (much more than a forward connected pot in the same position) and that kills the (amplitude of the) resonance peak. It's fine as long as it is either one pickup only or both full on, but any position in between has this problem.

I'm not saying it must be horrible, but I'm pretty sure that e.g. with two PAFs that would be insatisfactory as they rely on a good resonance peak.

uOpt,

Thanks for this insight, I think I'm picking up what you are putting down. Can you explain what you mean by connecting them backwards? Help me out here, my understanding that as soon as you connect the positives from the two pickups you are effectively putting them in parallel and there is not really a backwards (or forwards for that matter). What am I missing here? Can we reference the Jbass diagram above?

Thanks so much! I'm still learning the finer points of wiring, got the basics down its just when I try to realize my imagination it gets tricky...

[ArtieToo]

Re: Two independant volume pots for two pickups. No switch. How can I do it?

Hey Phil; I've actually come up with a way to accomplish this. I've already built and wired one prototype and it works. But it needs a little "tweak" before its ready for prime time. The problem now is locating the right pot. Bourns makes it, but nobody sells it.
I need this Bourns part #: PDB182-GTR01-105B0

The number after the "GTR" could be 01/02/03/04 and the designator after "105" could be either A2 or B0. You can Google those part numbers and you'll find the "104" version all day long. But not the 105 version. (1 meg)

[uOpt]

Re: Two independant volume pots for two pickups. No switch. How can I do it?

uOpt,

Thanks for this insight, I think I'm picking up what you are putting down. Can you explain what you mean by connecting them backwards? Help me out here, my understanding that as soon as you connect the positives from the two pickups you are effectively putting them in parallel and there is not really a backwards (or forwards for that matter). What am I missing here? Can we reference the Jbass diagram above?

Thanks so much! I'm still learning the finer points of wiring, got the basics down its just when I try to realize my imagination it gets tricky...

A guitar pickup is a low pass filter made up from it's capacitance, inductance and resistance. That is a second order LPF with a resonance peak at the cutoff frequency. Most most (not all) guitar and pass playing the peak is critical because it gives life and character to the pickup. It's not that you need as much amplitude on the peak as possible, it needs to be just right. Likewise, the frequency of the peak (which is the same as the cutoff frequency) need to be just right, high or low isn't necessarily better.

The passive pickup is high impedance and essentially defenseless against further load from capacitance and resistance. A load capacitance comes from the guitar cable, lowering the frequency of the peak (and the LPF cutoff) because it is simply added to the pickup's own capacitance. A load resistance is the volume pot (and the amp's input impedance). Less load is not better. You pickup has been made so that it sounds just right with a typical cable, and we all know that pots between 500 and 250 Kohm sound better (give the best amplitude of the peak) in most situations.

So, normally you connect the volume pot "forward", which means the pickup goes on the outer lug and the output goes on the slider. The disadvantage is that if you turn down one pot entirely all output is off. So you can't use it for blending pots if you don't have a switch. To do blending you have to connect "backwards" which is pickup goes to the slider and output is on the outer lug.

Now, at pot positions that are between full open and full closed there is a huge difference in resistance load.

Let's say you turn down the pot to 1/10th value, which really means 1/2 volume so it isn't that much. Your pot has 500 Kohm. So in the forward configuration you load your pickup with 450 Kohm load, but the backwards configuration has 50 Kohm load at the same pot position.

The load lowers the amplitude of the resonance peak, and while all is well with full open and full closed backwards pots any position in between will kill the resonance peak very quickly (leaving the pickup just as a low pass filter with no resonance).

Some guitar and bass situations can live with that better than others. Vintage single coil class pickups in parallel with each other have the cutoff frequency very high and then you don't really need a high amplitude resonance peak. The Jazz bass is an example.

[uOpt]

Re: Two independant volume pots for two pickups. No switch. How can I do it?

Random image of 2nd order low pass filter with resonance peak





There is more theory here but usual disclaimer, this author goes overboard with dismissing factors he can't compute:

http://buildyourguitar.com/resources/lemme/

[jimijames]

Re: Two independant volume pots for two pickups. No switch. How can I do it?

Hey guys,

So I'm stumped on how to wire this up. I want to be able to basically mix the signal of two pickups together using seperate volume controls for each (probably tone controls for each in there as well, tied to corresponding volume pot). Simply wiring them to the same output just does not work as it puts them together in a parallel circuit and everything gets crazy at that point. I think I read somewhere that you can do this with an active setup, but not passive. Does that make sense? It kind of does I suppose, I mean mixers do it.

Is a blend pot my only work around?

To sweeten the deal, one pickup is 250k and the other is 500k. How does that interact when sent to the same blend?

Anyway I'd love to hear some ideas from you all.

Thanks so much!
Phil

Well a potentiometer is just three lugs, and as you roll it up and down it bleeds off signal from the middle lug to the side lug. I don't know if that makes a lot of sense but get a multimeter up to one and you'll see what I mean.

Usually when you have two pickups on at the same time they're running in parallel anyway. That's the case with the gibson les paul, fender strat, tele, etc. Usually running two separate pickups in series is something you wire a push-pull for. Even in the diagram above the pickups are in parallel. If you really want them in series you have to wire it to where the neck pickup actually feeds into the bridge pickup rather than have them share a common terminus.

That being said a blend pot is a cool idea. You just wire up the 'hot' from each pickup to one of the lugs and then the third lug to the output jack.

It wouldn't be difficult at all to wire up two pickups in parallel where you control each with the volume pot. If you wanted to wire them in series like that you could do it as well, but whichever pickup was last in the circuit would have sort of a master volume - if you turned it down all the way you wouldn't be getting the signal from the first pickup in the series. That's not a feature you can work around either - when you're in series the entire circuit has to be closed or you aren't going to get any signal.

At least, that's my understanding of it. If it were me, I'd go for the two volume/parallel wiring which is super simple and would work really well.

edit: I see your question has been answered a lot better than I could have done. I'm also gonna go out on a limb here and say that if artietoo has come up with a solution I'm wrong about series wiring not being amenable to two volume pot configurations.

But hey, that's why I should lurk more and talk less. We live and we learn.

[Phil Gerke]

Re: Two independant volume pots for two pickups. No switch. How can I do it?

A guitar pickup is a low pass filter made up from it's capacitance, inductance and resistance............

uOpt,

Sorry it took me a while to get back here. What a great bit of info I really appreciate it! The Lemme article link was insightful as well. This has all really helped broaden and reinforce my understanding of the impact of loading down signals, as well as capacitance and inductance.

So I did some experimenting, I wired up the pots "backwards" and while it did function as it should have, i really did not care for the results. Combined with the fact that i have some switching for parallel and coil cutting it just turned into a mess Fortunately this is exactly what this guitar is for, experimenting. Maybe this would work better with single coils, but in my situation it just created a lot of un interesting sounds. At the same time is was very interesting from an education stand point. I think I'll leave this wiring to J basses.

Thanks a lot guys!

[uOpt]

Re: Two independant volume pots for two pickups. No switch. How can I do it?

uOpt,

Sorry it took me a while to get back here. What a great bit of info I really appreciate it! The Lemme article link was insightful as well. This has all really helped broaden and reinforce my understanding of the impact of loading down signals, as well as capacitance and inductance.

So I did some experimenting, I wired up the pots "backwards" and while it did function as it should have, i really did not care for the results. Combined with the fact that i have some switching for parallel and coil cutting it just turned into a mess Fortunately this is exactly what this guitar is for, experimenting. Maybe this would work better with single coils, but in my situation it just created a lot of un interesting sounds. At the same time is was very interesting from an education stand point. I think I'll leave this wiring to J basses.

Thanks a lot guys!

You are welcome.

I'm tempted to just order the new English edition of Lemme's book, not that I can't read his German.

It is too bad that Elektor publishing has decided to first make the effort for the translation and then price it according to a German Technical Book scheme, or whatever it is that makes a music book arrive at $45, which will put a pretty effective stop on both their revenue and on how US guitarists manage their guitars bleh