Behind the Bridge (BTB) Pickup Wiring Help - Jazzmaster

[benjaminr]

Hi there!

This is my first post and first project. I have never wired a guitar before, so I was hoping someone could either verify that my proposed schematic will work, or if it won't. If it won't, maybe a few tips would be helpful. Here goes...

I just dreamed up this wiring schematic for a BTB (behind the bridge) pickup set up on a Jazzmaster and was wondering if I could bounce it off a few of you. Disclaimer: I have no idea what I'm doing and I know I'm not treading new ground.

The idea is that when the upper SPST switch is in the 'down' or 'off' position, the rhythm and lead pickups function normally using the master volume and tone controls. In the 'up' or 'on' position, the rhythm and lead pickups still function normally with their own dedicated volume and tone controls, and the BTB pickup is engaged with dedicated volume and tone controls as well. This way, I can either get only the BTB pickup to function by rolling down the lead volume of the normal circuit, or I can blend all three pickups by adjusting each of their respective volumes and tones.

I know that was long-winded, but this is my first attempt at something like this, and based upon my marginal knowledge of switching and circuits, this schematic *appears* like it would work as described above. Lastly, I'm not sure, but I *think* my upper volume and control pots are wired correctly...

One of these is both circuits independently wired, and the other is for the BTB pickup independently wired and the normal circuit wired for master.

Any help at all would be super appreciated!!

[newey]

benjaminr-

Hello and welcome to G-Nutz2!

I don't know anything about behind the bridge pickups, other than that Sonic Youth used one at some point. And I'm at work, so no chance to vet your diagram at present. But I suspect that you'll need to replace the SPST switch in order to be able to switch between the two "modes" as you propose.

But I'll give someone else a chance to weigh in here . . .

[benjaminr]

Thanks for the warm welcome!

I'm new to this concept as well, but I've heard some pretty cool overtones and resonance from these kinds of set ups. Really though, where the pickup is positioned shouldn't affect the circuitry, provided it functions as desired. I'm open to any type of switching in order to make this work properly, though the simpler the better.

• Essentially, one "mode" is the normal bridge and neck pickup that can be switched via the three-way toggle and controlled by the normal volume and tone pots. This mode functions as if the BTB pickup is not even there.
  

• The other "mode" is the first mode functioning as it normally would, just along with the additional pickukp that is controlled by it's own volume and tone pots (the upper roller pots) without affecting the volume or tone of the other pickups.

Again, I really appreciate any help.

Cheers!

EDIT*

I think I'm getting closer.  I've changed the schematic to have the BTB pickup in parallel with the tone pot and the output of the upper circuit feeding the lower volume pot output and switched the pickup before the ton pot.  I think this would work, though I'm not sure if I would get dedicated volume/tone controls for each set of pickups.  Can anyone confirm?  Thanks!

[newey]

OK, I've had a chance to look at this a bit more. Several comments. . .

First, you threw me with the reference to a SPST "rhythm switch". While I've never had one apart, Fender's OEM diagrams here show this switch as a DPDT. Are you replacing the stock switch with a SPST? Or is your wiring already non-stock?

Your diagram seems OK, although I'm not clear on what seems to be a resistor wire in series with the blue wire, and labelled "80-220K". If you took that out, I think the diagram would do what you want it to. However, I think you will want the volume control for the BTB pickup to be wired "forwards" (IOW, with the "hot" from the switch going to the CW lug, the wiper going to the output.) It will work as shown, but the BTB pickup won't be fully "off" even with its volume all the way down.

But that's my take, let's get a confirmation before you start wiring anything. I could be wrong . . .

[benjaminr]

Didn't mean to throw you off! Yes, I am ditching the DPDT in favor of a simpler SPST (same switchcraft housing and same fit, just two lugs).

Also, the resistor is there because I have been told that without it, when both modes are functioning, either tone control will actually act as a master tone--I'd like to retain an individual tone and volume adjustment for each mode. Also, I was told that the value of the resister will affect volume output, hence 80-220k. I'd like to try 80k and see if I can retain individual tone control and not lose too much output.

As far as the wiring of the pots for the BTB pickup... Can you be a but more layman friendly (I.e. which lug is CW, IOW, wiper, etc.)? I do apologize and appreciate your patience, but I'm a complete newb.

Thanks for all of your help so far!!!

EDIT

A simple google search could have saved me the embarrassment. Wiper is center. Duh.

[newey]

Also, the resistor is there because I have been told that without it, when both modes are functioning, either tone control will actually act as a master tone--I'd like to retain an individual tone and volume adjustment for each mode. Also, I was told that the value of the resister will affect volume output, hence 80-220k. I'd like to try 80k and see if I can retain individual tone control and not lose too much output.

I'm not so sure about that. I think the resistor isn't going to do anything as far as the tone pots are concerned. It will cut your output.

When both "modes" are active, you will have both tone controls (and the vols, too) connected in parallel. They will interact, just like on a Les Paul, to a certain extent. I don't know of any good way around that.

There's no need to change out the switch for a SPST if you haven't already purchased a new one. If the old switch is functioning fine, you can use it the same way to do the job.

[benjaminr]

Thanks for the info.  I suppose I'll just live with some individual tone control loss (a BTB pickup's tone *probably* isn't going to be that important anyway).  However, does this mean that when the BTB "mode" is off, the upper controls will *still* affect the normal "mode" as the controls are wired together?

[ashcatlt]

The first two diagrams were exactly fine. They are functionally identical except that when the "Master" one has the normal V all the way down the whole thing goes silent.

A series resistor after the BTB's T control will tend to isolate it from the other two pickups, but you'd need yet another resistor to isolate the other T from the BTB, and there will be broadband attenuation and high frequency loss thanks to cable capacitance. Turning down either V pot accomplishes the same thing...

[newey]

This may help with your questions about potentiometers:

guitarnuts2.proboards.com/thread/6612/potentiometer-orientation

ashcatlt, who is much better at this sort of thing than I am, confirms that your diagrams are OK so you should be good to go.

I suppose I'll just live with some individual tone control loss (a BTB pickup's tone *probably* isn't going to be that important anyway). However, does this mean that when the BTB "mode" is off, the upper controls will *still* affect the normal "mode" as the controls are wired together?

No, because the switch takes those controls out of the circuit when the BTB pickup is switched off. It's only when both the BTB and one or both of the other pickups is active that you'd have the interaction. Again, this is no different than on an LP, so if you've ever played one, or a similar guitar, you may have noticed the interaction.

But thousands of LP players either don't know, or aren't really bothered by it. Many may never use their tone controls, or never use both pickups together. IOW, it's not that big a deal. And having the dual tones does allow you to "preset" the tones for the different pickups to a certain extent, and so can be valuable to have despite the interplay of the pots.

[benjaminr]

Thank you both so very much!  

I think I'll probably go with the third diagram, as it has only one connection to the output rather than two, though functionally it would be no different.  Also, I think having them wired in this way (as suggested) will keep the load on the circuit relatively close when switching between modes.  I'll be using the third diagram without any resistors--this will at the very least be an excellent starting point to move forward with.

Cheers!

EDIT*

Any more thoughts on whether or not I should rewire the upper volume pot to reflect the comments above?  (hot from switch to CW lug, output from wiper)

[ashcatlt]

I guess I'd probably rather have the controls on the far side of the switch so that they are removed from circuit when switched out, but I guess that's a matter of taste. Just be aware that with the third diagram, the position of both T controls will affect the output at all times.

Note also that there's no reason you have to actually run that second wire all the way to the jack in the first two diagrams. They could go the appropriate V pot lug same same.

I think you should leave that BTB's V pot wired "backwards" as drawn just to avoid confusion. Especially if you've got it on this side of the switch and with the "Master" arrangement of the other V control. You don't really need two kill switches, do you?

OTOH, since there is a switch for the BTB, I wonder if it wouldn't be nice to go back to the "backwards" wiring (what you called "Independent") for the N/B section so that you have to opportunity to get the BTB alone if desired.

At a certain point one wonders why we don't make that BTB switch also an ON-ON-ON...then what about series/parallel options...phase...

And like I said, any resistors you add will be essentially redundant to the V pots.

[benjaminr]

Thank you...

It would be nice to get the BTB on it's own from time to time, however I also was told that wiring that circuit in this way "notably changes the taper of the control as you roll back, and attenuates the high end in a way that can't be recovered with a treble bleed circuit."  I'm not interested in sacrificing the normal tone of my guitar if wiring it in this way causes tonal degradation.  However, it seems that what I've been told so far has not mattered all that much for this application.

[newey]

ash said:

I guess I'd probably rather have the controls on the far side of the switch so that they are removed from circuit when switched out, but I guess that's a matter of taste. Just be aware that with the third diagram, the position of both T controls will affect the output at all times.

Yeah, just to clarify, using either of the first two diagrams takes the pots out of the circuit when the switch is "off", but the third diagram, with the controls after the switch, doesn't do so. So I agree with ash, use either of the first two diagrams.

My prior statement may have confused the issue more, by not specifying which diagram I was referencing.

Since the BTB will probably be used more sparingly than the original pickups, why have its controls loading the circuit when not in use?

[JohnH]

I'd be interested to know what it is that a behind-the-bridge pickup, picks up?

[benjaminr]

It adds some nice ghost-like overtones and an interesting resonance to your sound, but honestly it's more useful for experimental sounds. Here are a few pretty cool videos of what you can expect:

mmguitarbar.tumblr.com/tagged/deepseadiver

[gitpiddler]

Mar 25, 2014 21:12:28 GMT -5 JohnH said:

I'd be interested to know what it is that a behind-the-bridge pickup, picks up?

The harp sounds between bridge and tailpiece.
Kinda like the start of 'Runnin w Devil'. The p'up screwed into the wood and hitting it behind the bridge-of the Korina Explorer, which he later cut into a V.