Can a resistor in series with a pickup turn a 500k volume pot to 250K?
- Thread starter glenn
- Start date
chris m.
Doctor of Teleocity
No. Not possible.
If I'm following what you are asking, no, you would attach a 500K (probably in reality a 470K or 520K) between the switch lug and ground. Say, if you want your bridge pickup to see an equivalent of 250K, put a 500K from the bridge pickup lug to ground. In the Bridge position the pickup would see 250K, in the neck position it would see 500K, and in the middle it would see, well... something in the middle.
A resistor in parallel with the pot can change (lower) the apparent value, and for a 500k pot a 470k resistor is about right.
1/Rt = 1/R1 + 1/R2 = 1/500k + 1/470k > Rt = 242k
This trick is typically used to make single coils "see" ~250k when teamed up with a humbucker.
Attach the resistor to the hot lug of the switch corresponding to the pickup you want to see 250 and the other end to ground. With a superswitch you can isolate the resistor to specific positions a lot better than with a standard switch.
1/Rt = 1/R1 + 1/R2 = 1/500k + 1/470k > Rt = 242k
This trick is typically used to make single coils "see" ~250k when teamed up with a humbucker.
Attach the resistor to the hot lug of the switch corresponding to the pickup you want to see 250 and the other end to ground. With a superswitch you can isolate the resistor to specific positions a lot better than with a standard switch.
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chris m.
Doctor of Teleocity
Yes, parallel works; series does not.
Thanks so much for straightening me out on this, guys -- it's greatly appreciated. Obviously, I'm really inexperienced when it comes to resistors, and with that in mind, I have a question: When you say to connect one end of the resistor to the hot lug, do you mean the toggle switch? The reason I ask is because I just tried that with the other end connected to ground, and it cut off the pickup. Obviously, I'm doing something wrong, but I can't figure out what.
The lug where the pickup you want to effect is connected. You want a 470K resistor (yellow - violet- yellow - silver (or gold)), or a 520K (green - red - yellow - silver (or gold)).
That effects both pickups, not just one as the OP wants.
editorjuno
Tele-Afflicted
Excellent, straightforward advice -- and don't let the math intimidate you, because there are handy on-line calculators that will do that for you: Parallel Resistance Calculator
R1 * R2 / (R1 + R2)
Yes I use a 249 or 270k. Fender has a diagram for this using a 270k resistor on a Tele with a neck Humbucker and Tele Bridge using two 500k pots. Adding the 270k resistor to the Tele Bridge which makes the bridge see the circuit as apprx 250k pots.
editorjuno
Tele-Afflicted
"249k" may well be the actual, measured value of a resistor -- e.g. a 270k part with 20% tolerance that measures on the low side of that tolerance -- but good luck finding one with that nominal/marked value, because AFAIK they don't exist commercially (other than as a custom precision part). A 270k fixed resistor across the outer terminals of a 500k volume pot would not result in "apprx 250k" -- the math says that the resulting de facto value of the pot would be about 175k, which may work well for a particular guitar but is on low side compared to what a typical Tele bridge pickup expects to "see." As for the tone pot, it only figures in as a load above the high-pass frequency determined by the tone cap's effect on the circuit, and its effect on the overall load also depends on the position of the tone knob -- for the lower frequencies that comprise the bulk of the signal, for all intents and purposes that cap takes the tone pot out of the circuit.
bradpdx
Friend of Leo's
This will be a whole lot easier if you just swap out the 500K pots for 250Ks. You can add parallel resistors (as discussed) but the results will not be quite the same, especially with regards to taper.
editorjuno
Tele-Afflicted
That would defeat the OP's purpose, which was to have his neck humbucker "see" 500k and his bridge single-coil "see" 250k. In my experience, the change to a volume pot's taper when switching in a parallel resistor is noticeable, but tolerable -- a bit different, but perfectly usable. In fact, even a linear pot can work pretty well as a guitar's volume control, and in fact there have been quite a few production guitars with a linear volume pot and an audio taper tone pot.
Mreilander
Tele-Holic
^this. It will only be the proper overall resistance when the pot is turned all the way up. It will significantly change the taper of your pot(s) for anything that is not full bore.
editorjuno
Tele-Afflicted
An electric guitar's volume control is wired as a voltage divider and therefore always presents its nominal "proper overall resistance," to the pickups, regardless of the position of the volume knob or whether a parallel fixed resistor is involved. Its resistance varies as per the de facto taper on the output side of the circuit (center terminal of the pot and signal ground) connected to the jack, not the input (outside terminals of the pot, one of them grounded) side that connects to the pickups via the selector switch.
Big-Tele
Tele-Meister
I might try the 470k resister idea. What type of resister would you use?
Big-Tele
Tele-Meister
Looks like I can get a 510K metal film 1/2 watt resister that will give 252K. just about spot on.
Any 1/4 watt approx 500k is fine. 1/2 watt, too, just overkill. There's near zero voltage to worry about.
http://www.electronics2000.co.uk/calc/series-parallel-resistor-calculator.php
http://www.electronics2000.co.uk/calc/series-parallel-resistor-calculator.php
