Guitar mod idea; does this work?

[jakeac5253]

I've got an idea for a guitar mod and I'd like to know if this will work. Here are the details:

Fender Strat HSS with Fender USA 5 way switch and 500k volume, 250k tones. Wired with no tones on Bridge pickup, middle and neck tones.

I'd like for the Bridge humbucker to see the 500k pot as it is, but I'd like for the middle and neck pickups to act as if there were a 250k volume pot instead. Here is my Idea:

Wire the switch normally, but strap a 500k resistor across the switch contacts for the middle and neck pickups individually (two resistors total). According to my calculations, it works. What do you think? How about positions 2 and 4, will they sound natural or will the effect be lost in those positions?

[trevorus]

If you use a 500K to drop the apparent load the middle and neck pickup see, just remember, in position 4 (or is it 2?), your humbucker will see a 250K volume as well. Might sound fine.

[jakeac5253]

If you use a 500K to drop the apparent load the middle and neck pickup see, just remember, in position 4 (or is it 2?), your humbucker will see a 250K volume as well. Might sound fine.

Thanks for the response. Why is that?

[trevorus]

Think of it electrically. When you have the bridge and middle (which has that 250K resistor hooked to it), it is now connected to both. I actually did something very similar in an HS tele with a Duncan Broadcaster bridge pickup and an Antiquity neck 'bucker, to alter the bridge pickup to be a litte smoother, and the neck a little brighter.

[jakeac5253]

I think that would work. I want the bridge pickup alone to be hot and tight, but when I think about the times I am going to use the second position I think that it being a bit warmer could be a good thing.

[Mark Hammer]

You do realize that all of this 250k/500k/1M fetish is only meaningful when the volume pot is maxed? Turn down any of them from 10 to 7 or 6, and you have significant loading, unless you have a treble-bypass cap or something similar in the volume circuit.

Is the use of a 500k pot producing undesirable tone for you at the moment? Is the urge to create an effective 250k load because you think it will sound better, based on what you've heard, or becase you've tried it and like it?

[jakeac5253]

Well I am still awaiting parts to arrive so that I can build the guitar, but I do prefer the tone of singles through a 250k pot and not a 500k pot and would like to emulate both within the context of the same guitar. My Bridge humbucker selected alone needs to see the 500k volume and straight to output, there is no question about that. The Middle and Neck singles I would like to have individual tone knobs and would like to simulate them seeing a 250k load and not a 500k load if at all possible.

My original idea was that I would put the ~500k resistor across the + and - pickup leads to act as a load but then I thought of two things that I didn't like about that. First is that there is still an initial loading of 500k on the pickups, and second that I'm not sure if either pickup could effectively be turned completely 'off' when there is a resistor constantly loading it. I got advice from someone who said to have the resistor go from the - lead of the pickup to the pot ground network. This made more sense and I was considering doing that. The only thing I am worried about now is that when the neck and middle pickups were selected the load would drop to below 250 I believe (not sure on this). Although this could create a cool, creamy tonality all its own for all I know and I'll never know until I try.

Knowing my goals and thought process throughout the build, what would you suggest I do? I do have a few volume mods lying around in my parts drawer, but I would rather go 'au naturale' with this guitar if at all possible. If you need more information, please don't hesitate to ask.

[jakeac5253]

OK so I went ahead with the mod as planned and I have a small problem, probably pot related, what do you think. Here is a quick rundown/recap:

Pickups:
Bridge - Duncan Custom
Middle - DiMarzio SDS-1
Neck - DiMarzio Area 58

Electronics:
Switch - Fender USA 5 way
Volume - CTS 500k Audio
Mid Tone - CTS 250k Lin
Neck Tone - CTS 250k Lin

Misc:
470k 1/4w resistors wired from Mid and Neck pickup to volume pot ground.
Tone Caps - .047 Ceramic Disc 1 per Tone pot.

Wiring configuration: Strat Standard for HSS config, but Tones were wired like a Les paul using one wire soldered to the switch contact with the pickup's hot lead. I did this so that both Mid and Neck tones would be completely isolated from one another, but I may change this if need arises.

Here's a problem that I have. The Tone knobs seem to hold 80% of the sweep between 0 and 2 and the remaining 20% disbursed over the rest of the sweep. Do you think that this is due to the resistors being placed across the pickup causing conflict? Or that I should have used Audio Tone pots instead?

[Gtr_tech]

Use audio taper for *all* the pots. If you don't....you'll get the behavior you are experiencing. And get rid of the gnd wire connecting all the pots together on the back. Use the vol pot to gnd all the p-ups to and run the jack gnd and string gnd to that. The foil shielding you have will ground the tone pot casings and then theres a single gnd path. Lessens the occurance of gnd loop induced noise. Its called "star grounding" if you want to research it.

[jakeac5253]

Use audio taper for *all* the pots. If you don't....you'll get the behavior you are experiencing. And get rid of the gnd wire connecting all the pots together on the back. Use the vol pot to gnd all the p-ups to and run the jack gnd and string gnd to that. The foil shielding you have will ground the tone pot casings and then theres a single gnd path. Lessens the occurance of gnd loop induced noise. Its called "star grounding" if you want to research it.

Yes, that's true, I didn't think of that at the time, but that one green wire does violate the Star Ground concept. Thanks for the advice, which would you prefer to do if this was your guitar? Get rid of the wire which bridges the Mid and Neck tone pots and instead run a wire from the Mid to Vol pot to complete the Star Ground? Or should I pull the two green wires completely from the circuit?

[Gtr_tech]

As long as the foil connects to the pot casings (check for continuity with yer meter to verify) you don't need the wire connecting them. Choose a single point to gnd everything to....which is usually the vol pot.

[jakeac5253]

As long as the foil connects to the pot casings (check for continuity with yer meter to verify) you don't need the wire connecting them. Choose a single point to gnd everything to....which is usually the vol pot.

Thanks again. Now that I am thinking about it, in order for the continuity reading to mean anything, I would first have to unsolder the green connections right? (Glad I color coded it because it's really helping things )

[jakeac5253]

Alright so I removed the green wires completely and found that all pots are connected via the foil shield. Good news. Here is the bad news. The noise that I was experiencing with the Humbucker engaged which I wrongly accused as being ground loop based, remains. The humbucker produces a cycling kind of white noise, I can make a recording of it if need be. The pickup also sounds pretty light in the bass for a bridgebucker and that's worrying me as well. I think the problems may be related, but I can't be sure. The meter shows continuity between volume pot ground and all points where it needs to be grounded to i.e. output jack, string ground (tailpiece), and the screw ground in the back of the cavity.

As I said previously, the pickup is a Seymour Duncan Custom and is wired standard as a non-splitting humbucker. The black lead is soldered to the first switch contact, the red and white leads are twisted soldered insulated and taped to the bundle, and the green and bare wire are soldered to the back of the volume pot. I don't have the common's bridged on the switch because I am not using the other side of the switch for anything, is this alright?

[David Schwab]

As long as the foil connects to the pot casings (check for continuity with yer meter to verify) you don't need the wire connecting them. Choose a single point to gnd everything to....which is usually the vol pot.

That's a poor way to wire things up. You are relying on a mechanical connection to establish ground. If the connection becomes lose or oxidized, there goes your ground.

All the backs of the pots should be wired together. You do not need a single ground point. This is a based on the myth that you can have a ground loop in a guitar, which you can't, because it only has a single ground at the output jack. The fact that his noise didn't go away shows this.

Ground wires do not lead to ground. Ground wires ARE ground.

[David Schwab]

Alright so I removed the green wires completely and found that all pots are connected via the foil shield. Good news. Here is the bad news. The noise that I was experiencing with the Humbucker engaged which I wrongly accused as being ground loop based, remains. The humbucker produces a cycling kind of white noise, I can make a recording of it if need be. The pickup also sounds pretty light in the bass for a bridgebucker and that's worrying me as well.

It sounds like the humbucker has it's two coils out of phase (in phase actually). You have it wired up correctly though, but just to see, swap the green and red wires and see if it doesn't get quiet and sounds fuller.

Also make sure the base plate has continuity to ground via the bar wire.

How is your volume pot wired? I don't see a connection to the center lug.