Alan Holdsworth wiring adaptation

[nerd]

Hi there.

I'm changing pickups in one of my older PRS guitars to 59/09. This is the wiring diagram I'm using.



In a nutshell - this is a McCarty wiring diagram with partial splits with resistors on Push-Push tone knob. Nothing overly complicated but...

...I came across Alan Holdsworth wiring as seen below



Further description here:

m.facebook.com/groups/allanh/permalink/1469991359790503/

What got me thinking is a resistor that keeps minimum of 12k resistance above ground when the tone pot is down to zero. 12k is around 5% of 250k tone pot value so if my math is correct I should be aiming for around 25k resistor to do it with Humbackers and 500k tone pot in my guitar.

Thing is - the tone pot in Allan's wiring is done differently than it's made in my McCarty so here's the question:

Will I archive same thing by cutting ground connection on outside lug, existing tone pot ground reference and placing resistor from there to ground?

Thanks

[Yogi B]

Jul 16, 2021 9:48:25 GMT -5 nerd said:

What got me thinking is a resistor that keeps minimum of 12k resistance above ground when the tone pot is down to zero. 12k is around 5% of 250k tone pot value so if my math is correct I should be aiming for around 25k resistor to do it with Humbuckers and 500k tone pot in my guitar.

It doesn't quite work like that, not with a tone pot.

When a tone pot is turned all the way to zero, no matter the total resistance of the pot, the portion of it that is in series with the tone capacitor is zero. So if the sound you're after with the tone pot on zero is that of the tone cap in series with 12k, the resistor will still need to be 12k.

Put another way, with a 250k pot the 12k resistor changes the range of the tone control from the standard 10 - 0 to about 10.1 - 3. Adding a 25k resistor with a 500k gives the same range relative to the 500k pot, 10.1 - 3. However "3" on a 500k tone pot sounds about the same as "5" on a 250k.

Thing is - the tone pot in Allan's wiring is done differently than it's made in my McCarty so here's the question:

Will I archive same thing by cutting ground connection on outside lug, existing tone pot ground reference and placing resistor from there to ground?

Essentially, yes. However in the original diagram, the outer lug isn't just grounding the tone cap, it's also grounding the (presumably?) bridge humbucker and providing a ground path from the case of volume pot to the chassis of the switch, the case of the tone pot, and the partial coil splits. Cavity shielding (if present) should be doing this too, and if the only reason was to ground the case of the tone pot for the purposes of shielding, then I'd say that'd be good enough — but since you've got the coil splits too, a proper solid connection would be preferable.

So yes, while you can replace the wire connecting lug 1 of the tone pot to its case with the resistor — you'll also need to move the other three leads currently connected to that lug:

• The white wire of the bridge pickup could be moved to go directly to the case of the tone pot, but if it were me I'd probably have it join the black wire from the neck pickup over on the volume pot (such that wires with similar functions are grouped in the same place);
• The ground wire from the case of the volume pot & the wire to the switch's chassis should both be moved, you could connect both directly to the case of the tone pot — alternatively you could connect the volume's case directly to the switch then connect the switch the tone pot, as that'd be one less wire that you'd need to solder to the case of the tone pot.

[nerd]

Thank you very much.

I couldn't dream of better answer to my question