Switching between 250k and 500k Pots with P-Rails

[CamH132]

I have a guitar that i've just installed a single coil in the neck and a p-rails in the bridge with a standard 3-way pickup switch, a 3-way dpdt switch to switch between the 3 p-rails options and 500k master volume and tone pots. My issue is that the neck single coil and the p90 coil in the p-rails currently sound too bright with the 500k pots. I would usually just change to 250k pots but i'm worried that might dull the p-rails humbucker too much.

I'm planning on putting a 510k resistor in parallel with the neck single coil and am wondering if it's somehow possible do the same thing to the p90 side of the p-rails - but have it wired up on the dpdt switch so that the resistor only comes into the circuit when the p90 option is selected by itself?

Alternatively, am i able to just install another mini switch which gives me the option to switch in a 510k resistor in parallel with the volume knob to effectively switch between having a 500k and 250k volume knob?

Cheers

 

[Liko]

Re: Switching between 250k and 500k Pots with P-Rails

I did something similar to this with my own P-rails, except I did it on the tone circuits. Get yourself a DPDT pot, a 500K resistor and two tone caps (22nF and 47nF). One side of the switch will control which tone cap is used, the other will switch the parallel resisor in or out of the circuit. The net result, in one DPDT position you have a Gibson-spec 500K/47nF tone circuit that works well for the humbucker modes, in the other a Fender-spec 250K/22nF circuit that works well for the rails. Either works well for the P-90s, the Fender tone circuit gives you a more Tele-ish tone while the Gibson circuit is classic Goldtop.

This same arrangement, only sans tone caps, would work just fine for the volume pot too, you just wire in the resistor to the switch and you change the value of the pot from 500k to 250k. I didn't go this far on my own P-Rails axe because you can always back off a bright guitar with the tone controls, and I wanted a neck-on switch for that DPDT (it's an HSH Strat so I wanted neck+bridge and NMB modes).

Best I have on my phone at the moment is a photo, lemme find the wiring diagram again...

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[CamH132]

Re: Switching between 250k and 500k Pots with P-Rails

The switchable tone circuits sounds like it might be pretty close to what I'm looking for. What would be the difference between switching the tone pot from 500k to 250k rather than the volume?

Would it maybe be a better idea to wire up the DPDT switch so that it switches both pots to 250k? I'm currently getting a lot more tone roll off with the 500K/47nF combo than I'd like so I'm not sure if there's really any point to having the tone cap switchable to 22nF - unless it affects the resonant frequency when both knobs are at 10 (which I think is where my main issue currently lies)?

Did you have any issues with the taper of your tone pot once installing the switchable tone circuit?

 

[Liko]

Re: Switching between 250k and 500k Pots with P-Rails

It's subtle especially with the pot value change counteracting it, but the smaller cap value does raise the resonant peak. The rails just don't sound quite like a Strat until I pop the pots up.

As for taper issues, not too bad.

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[GuitarDoc]

Re: Switching between 250k and 500k Pots with P-Rails

You say the P-90 coil of the P-Rail sounds bright? Are you sure that it is the P-90 coil and not the rail coil you are listening to? My experience with many P-Rails in many different guitars is that the P-90 coil NEVER sounded too bright. The rail coil is a different story however, and the reason I ended up putting an A8 mag next to the rail (to beef it up so it could somewhat keep up with the P-90).

 

[CamH132]

Re: Switching between 250k and 500k Pots with P-Rails

I have tested the wiring of the 3 way switch by physically tapping on the coils with an allen key while switching between them and can confirm that it is the P90 side that I'm finding too bright. I don't use the rail coil very often, but I've found that while it doesn't have as much output as the P90 coil, the brightness hasn't been an issue - which i had just attributed to the fact that it's positioned slightly further away from the bridge. (Which now that I think about it is a little bit odd considering I'm finding the neck single coil way too bright at the moment)

Any of my other guitars which have a bridge P90 also use 250k pots - so it may be that I am just used to that sound and am not a fan of the little bit extra that you get with the 500k pots. When I find some time over the next couple of days I'm going to temporarily wire up parallel 510k resistors over the pots and see if that fixes the issue.

 

[GuitarDoc]

Re: Switching between 250k and 500k Pots with P-Rails

Oh, so you have the P-Rail mounted with the P-90 coil next to the bridge. That explains a lot.

When the P-Rails first came out, I did a LOT of experimenting with them. I tried them in different mounting positions/orientation (both neck and bridge models), and just about every magnet combination possible (you know that there are 2 mags in the P-Rail, right). I found that for the greatest versatility in tones using all four tonal possibilities of the P-Rail (and using a Triple Shot mounting ring to access these 4 tones easily), the bridge pup needs to be mounted with the rail coil closest to the bridge. Of course, in comparison to the P-90 coil, the rail coil sounded weak and bright/thin in this orientation. So I put an A8 mag next to the rail coil to beef it up in tone and output, and kept the A5 mag next to the P-90 coil to keep the highs as present as possible. I definitely kept the 500k pots with this pup. In typical humbucker mode (series), the P-Rail is a very heavy sounding pup. 250k pots would only make it sound muddy.

 

[Liko]

Re: Switching between 250k and 500k Pots with P-Rails

Oh, so you have the P-Rail mounted with the P-90 coil next to the bridge. That explains a lot.

When the P-Rails first came out, I did a LOT of experimenting with them. I tried them in different mounting positions/orientation (both neck and bridge models), and just about every magnet combination possible (you know that there are 2 mags in the P-Rail, right). I found that for the greatest versatility in tones using all four tonal possibilities of the P-Rail (and using a Triple Shot mounting ring to access these 4 tones easily), the bridge pup needs to be mounted with the rail coil closest to the bridge. Of course, in comparison to the P-90 coil, the rail coil sounded weak and bright/thin in this orientation. So I put an A8 mag next to the rail coil to beef it up in tone and output, and kept the A5 mag next to the P-90 coil to keep the highs as present as possible. I definitely kept the 500k pots with this pup. In typical humbucker mode (series), the P-Rail is a very heavy sounding pup. 250k pots would only make it sound muddy.

I considered this layout on my HSH P-Rail build, but as of when I put it together I decided P-90 down. It made the switching scheme I have for the P-Rails work exactly the same for the bridge as for the neck (which I did flip for better neck-mid quack), it gives me the same polarity in the outermost positions, so if I tap the middle Classic Stack I get hum-cancelling behavior in the quackiest combos, and the extra beef of the P-90 is just what I wanted for a "Texas Hot" setup when I set it up as an SC Strat.

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