Oddball Potentiometer questions

[bldypsnt]

I made up a wiring diagram for my '72 Bluesbird (LP Style layout) where instead in the neck and tail positions the volume is directly on a master volume, but in the middle position the pickups go through a blend pot (balance controller first). To make this work I have each pickup going to a tone pot (never seen this done before, but see no reason why it would not work) and then there are leads to the toggle switch AND through the balance controller to the toggle. I'm using a SG custom toggle, which acts like an on/on/on switch. So I'm wondering if with the P/U always leading to the blend pot (though the signal is not going out to the master volume) whether or not the blend pot is going to constantly be bleeding signal off to ground. The way I understand it (and I'm an idiot when it comes to wiring) is that it's really no different than a tone pot without a resistor at that point, which should do squat. I'd like to make sure before I go soldering everything together though. I'd rather not have to fool with the balance knob when switching.

[bldypsnt]

Ack, I meant "capacitor"....a tone pot without a capacitor *hitting myself*

[JohnH]

bldypsnt - Welcome to GN2

It would be easier to help if you could post a diagram of your wiring. To do this, you place it somewhere on the internet, then add a link to it here.

John

[bldypsnt]

Gotcha, here's a link.
i45.photobucket.com/albums/f60/bldypsnt/72BluesbirdDiagram.jpg

[JohnH]

bldypsnt

Ok, your diagram is clear enough. BTW, if you put the link between image tags, it will appear in the thread. (IMG and /IMG, inside square brackets)

It was just as well you came here, since I think there are several problems with the wiring design, and I can't see an easy fix to get fully to what you want, which I assume is to have the blend control mix the pups, but only be active in the middle position of the on-on-on?

So whats OK?

The phase switch is OK.
The idea of switched caps on the tone controls is fine, and the way you have it on the neck should work. I'm not following the bridge version of it though, which is wired to three instead of two pot lugs

Problems

The usual way to wire a blend pot will make it provide full output in the middle (detent) position for both pups, and one pup diminishes as you turn it left or right. It does this by having half of each track with 500k resistance, and the other half almost zero resistance, and the zero part is on opposite sides for the two seperate tracks of the dual pot. If this is inserted in the circuit after each pup, then the pups are reduced by it in all positions of the selector toggle

What you have is an unusual idea, but as far as i can see, with the blend in mid position, both pups are shorted together through the low resistance parts of the blend pot, so you get N and M in all toggle positions, and with the blend at one end, it will always be shunting the respective pup.

Why does the bridge setting send the signal through part of the tone pot?

Finally, the master volume is odd, wth only two lugs connected

I would also ask, if you have a classic guitar from 1972, do you really want to change it? Even a simple and well executed retrofit can reduce its value.

John

[bldypsnt]

Forgive me because I'm going to be working in reverse of your message, John.

The guitar is in the process of a cosmetic overhaul as it is to rectify a previous owner's VERY shoddy refinish, so there really is no harm that can come of rewiring her. I have saved the original harness in case I want to refit it.

Here is a revised version of my diagram. I made the original a bit hastily and botched the master volume ground and the bridge pup to 3-way switch connection at the bridge tone pot in the process.


I'm not completely clear on what you're saying regarding the blend pot. What I gather is that having the blend pot wired in at all times (even when it's not being used to balance) will reduce volume because it IS constantly grounding some signal. I can accept this so long as there's a fairly constant volume.

I'm trying to see what you're saying about the belnd pot and shorting out the pickups. I made the drawing on the assumption that one of the pots that was stacked was inverted, which explains the 'x' wiring on the pot. I'll have to get a multimeter and check, but if the pots are not mounted oppositely, then I can see that a " I I " (<----ascii art) wiring layout on the blend pot would be right.

I wanted to isolate the balance altogether in the neck and bridge positions, but the trick has been wiring the 3-way switch. If I could use a diode (not sure what rating or how this would affect sound) I could probably make it work this way. For lack of technical knowledge I just split the lead from each pup to go to both the master volume and balance simultaneously at all times. Thanks for the help you've given so far, John. I'm a steam-plant mechanic, not an electrician. So any and all help goes a loooong way

Ray

[ChrisK]

These might help you;
guitarnuts2.proboards45.com/index.cgi?board=schem&action=display&thread=1158705194

My post here will give some insight into blend pots (your analysis is essentially correct);
guitarnuts2.proboards45.com/index.cgi?board=schem&action=display&thread=1145315219

as will this;
www.stewmac.com/freeinfo/i-4137.html

[JohnH]

Bldypsnt - the second diagram appears to be the same as the first.

I had a think about what you are proposing. I reckon that to get the blender out of circuit, so it doesn't affect the single pup settings, will need more switch poles. There are 4 pole on-on-on switches which might do it. I havent seen one myself , but like this:

www.guitarelectronics.com/product/SWT36

It's like two DPDT on-on-on's, side by side on one switch. Lets think about that for a day or so. Anyone with a bright idea please post!

John

[JohnH]

Further to the above, this I think could work, using a 4 pole on-on-on toggle:



You'd put the pups directly wired to the tone controls, one with a phase switch, and connected to this switching where shown, and also to ground. The output goes to the outer lug of a normal volume pot. I'm showing the switch in the central position, where the blender works. In the up or down postions, one or other pup is directly to output, and the blender gets cut out as required.

cheers
John

[bldypsnt]

Yes, I think you are right. A twin dpdt (on/on/on) could work just fine. I like my switchcraft switch though... so after much thought I came up with a different approach. Rather than switch to and from the blend pot, why not have it going all the time? Just switch what pickup is going to which leads (neck or bridge to just one blend pot input or both). The output should be constant. Your thoughts?

[sumgai]

bldyspnt,

First, I don't believe I've had the pleasure..... to these here forums! Sorry I was out of the office when you called the first time, almost two months ago.

Your most recent diagram suffers from a revisional error - you now show the Master Volume's wiper as being connected to the output of the Blend pot, it is no longer on the switch. This results in the Blend pot never being bypassed, it'll always be in the circuit! In fact, when you switch to Neck or Bridge only, both sections of the Blend pot are now in the circuit - twist the knob either way, and the volume goes down. The DP3T switch is, for all intents and purposes, null and void.

BTW, John.... bldypsnt's DP3T switch is the classic Gibson pickup selector switch. Your suggestion is the best solution, wiring-wise, but there's quite a bit of difference when it comes to operating the two items, I'm sure you'll agree. ;D

Which brings up the next possible solution.... bldyspnt, are you willing to subject your switch to some surgery? With the addition of some leaves, I believe we can make this work, but not in it's current incarnation, sorry to say.

And as you'll get to know, I'm the Board's resident perverse sob that always has to go out of his way to do things differently. The following will make John and unklmickey howl, but try this, just for an intellectual exercise...... I can accomplish your goal, with your switch, if you're willing to accept hanging Hots.¹ ;D See if you can arrive at that solution too. And more so than usual, I have a cure for that particular ill.

HTH


sumgai

1. A hanging Hot is where one lead of a pickup is connected to the output, and the other lead is ungrounded. Acts a bit like an antenna, increases the chances of picking up hum.

[bldypsnt]

Alright, here's the latest and (hopefully) final revision. I stopped trying to be clever with the wiring. Instead I modified my pickup switch. When the switch is not in the center position, the inputs, combined output, and ground lead are all isolated. I tested the switch with a multimeter and it seems to work just fine.

As for the last attempt. I tend not to agree with Sumgai's evaluattion. Having both pots of the balancer on at all times I don't think would decrease volume when turning the pot. The resistances in the pots when I tested it add up to around 500kohms when wired this way, but I do tend to think that since half the signal is sent to ground, when either pickup is selected alone the volume would be significantly lower since there is less total input current...it's academic at this point.

So I took your suggestion Sumgai and did surgery on the switch. I have a spare Switchcraft around here, but adding leaves didn't look like it was going to make it work the way I wanted it to. So I cut some strips from a popsickle stick. I glue two strips together, then glued one end to the inside of one of the long leafs. On the other end I drilled two holes and put two cut-off nails through and glued them in place. Then I built up some solder on the nail heads and soldered a wire to each nail. For the other contact side I took one stipr and wrapped two thin strips of copper foil around with the same spacing I used for the nails. This wood piece is glued to the outside of the other long leaf for spacing considerations. Then I soldered leads to the foil and made a solder buildup on the inside portion. I filed the solder buildup a little to make sure both contacts touch where they should at the same time. It doesn't look pretty, but from the wiring standpoint I think it's the best way using what I have. So thank you all again, and please let me know if you still see anything wrong.

[sumgai]

HOLY BATS, SMOKEMAN!!!!

Now that's what I call 'taking the ball and running with it'. No muss, no fuss, no excuses, just straigthforward logic applied to the task, and out comes a beauty of a solution.

bld, no further analysis is necessary, your circuit will work as designed (given proper implementation, of course).

Sir, you are truly a Guitar Nut of the First Order!


sumgai

[JohnH]

Clever stuff - well done!

Just one suggestion would be that for a single master volume, it is better to put the switch to the outer lug and take output from the centre lug of the volume pot.

John