Single/Paralell/Series with a Pot

[jhng]

Ok, here's the idea:




What do folks reckon? My hope is that the way the relative impedance of each pup varies, and the way the voltage splitting works, will result in a smooth and useful transition from just Pup 1, to both Pups in paralell at the halfway point, to both Pups in series at the other extreme.

Not sure about (a) the value of the fixed resistor;
and (b) whether having such high resistances in the circuit will screw up the tone or effect the way the guitar interacts with the amp.

This is the overall circuit I was thinking about incorporating it into:




The switch is a Tele-style threeway. Positions are B, B/N (parallel), and N. B and N pups each have their own dedicated "tone" control wired for "single, parallel with Middle, or series with Middle" (neither is active in position 2).

Hastings

P.S. JohnH- I had a look at your Tonemonster2 mod: Simply brilliant!

[UnklMickey]

Hastings,

i suspect 125k is very much the wrong value.

it's too big when the pups are in parallel.

it's also a bit too small when they are in series.


so what to do?

i hijacked your drawing, and made this change. it won't help much with your application, but in a 2 pup arrangement it might work well.

i haven't tested it, but it makes sense on paper. using a single control, ganged pot, both sections rotate from the same shaft. when you rotate to the parallel config, the right half of the pot will be at it's lowest resistance. when you go to series the right half will be at 250k.

as i am writing this, i'm also thinking that the pot would work better if it is logarithmic. with the slow part of the taper on the left. that way there would be much less than 125k in series with pup 1 when the pot is in the middle.




no promises, but i think it's a step in the right direction.



unk

[RandomHero]

Implement this drawing in a H/S/H guitar with three knobs a push-pull pot on the volume knob and you've got a whole new kind of tone monster...

I personally would use the push-pull as a neck on switch, and apply the ganged pots each to one of my 'buckers. That would be some -flavor-!

[JohnH]

I think Unk is right. A pup feeding through a 125k resistor (with a total impedance of say 130k ) cant compete with another pup directly connected in parallel, which only has say 5k resistance .

In fact, adding a resistor in series with one pup, is a good way of fading that pup down in a parallel combo.

Unks version keeps both pups seeing the same load and is symmetrical. I think whether it is a good idea or not would depend how the pups perform with 250k of load, which I suppose is a common value for pots on Sc pickups. The risk in feeding signals past various resistors is that they loose their 'edge' (Bono would be sad)

With Unks version, what would happen at a mid position? Say for a linear pot. If you imagine the 250k pots as two 125k resistors and consider each pup in turn. I imagine one pup as a voltage source and the other as a low resistance, work out the contribution from each, then add them. The result is, about 2/3 of the signal from each pup. added together, you get 4/3.

In a parallel combo you get the average of the two pups, ie 1/2 of each, so total = 1. In a series combo, you add 100% of each so total = 2. So this mid position is indeed between series and parallel. Don't know what it would sound like though.

Hastings - thanks for kind words on TM2

John

[jhng]

Thanks guys. My understanding of how pups interact with loads is a bit dodgy so your comments are most illuminating.

However, I'm not sure I've communicated the intended functionality properly. I think I need to clarify the thinking!

The Pups are only in parallel when the pot is turned HALFWAY down. I.e. impedance for EACH pup is 125K plus (say) 7k.

At one extreme Pup1 is 7k and pup 2 is 7k+125k. I hope you only hear Pup1.

At t'other extreme the pups are in series (with 125k in paralell with pup1 and 250k in paralell with pup2). I'm pretty confident that this series element will work.

In view of John's comments on feeding signals through resistors maybe a value of 50k for the fixed resistor. Then the pups would be in parallel when the pot is twiddled to about 8.

Hastings