Mismatched potentiometer values

[boldarrowoftime]

I'm currently in the process of my first DIY project and could use some advice. I've got an old Peavey Falcon (Strat type, SSS, 1 vol, 1 tone) that I'm overhauling. I'm replacing most of the electronics and while I'm at it, adding a rotary switch that will act as an on/off, phase, and parallel/series switch for the bridge. I'm going to be putting this switch in the position of the volume pot, so I'm going to be using a concentric pot as a master volume and master tone.

I've read that it's best to use 500k pots when adding series switching to counteract the loss of highs, but I'm hesitant that it'll become too bright in parallel. My choice of concentric pot is 250/500k or 500/500k. Am I correct in thinking that 250/500k combination would sound about half way between a pair of 250k's and a pair of 500k's in terms of brightness? And if so which should I use for the volume and which the tone? Are there any advantages to using matched values that I may lose with the 250/500K?

This is both my first project and first post on this board, so, uh, hello and sorry if this is really basic stuff.

[farren]

I can't help you much, but 500k and 500k gives you 250k, and 500k and 250k gives you 167k (though obviously your pots may well test far below advertised resistance.) Additionally they'll be in parallel with your amp's input resistor, which is probably 1M. I can't say 500/250k would be halfway in between 500/500k and 250/250k because the perceived difference in the loss of high frequencies isn't necessarily linear, but you will certainly notice.

Personally, I would go with the higher pot values (though I am a humbucker guy.) Passively, you can easily take away highs, but you can't generate greater brightness and presence. Best to err on the side of brightness, IMO. Depending on your wiring decisions, you may be able to put resistors in certain places to simulate a different load in certain switch positions (such as parallel) to tame brightness. Someone who actually knows what they are doing can help you if that interests you

As for any issues with mismatched pot values, I can't think of one. Perhaps if you wanted, say, a bridge tone control and neck tone control that respond in near identical faction. In any case, you violate no rules by mixing and matching.

I'm new here as well and am likely as basic as anyone here, but welcome

[newey]

bold arrow-

Hello and Welcome to G-Nutz2!

farren said:

Passively, you can easily take away highs, but you can't generate greater brightness and presence.

True.

And:

Depending on your wiring decisions, you may be able to put resistors in certain places to simulate a different load in certain switch positions (such as parallel) to tame brightness.

A resistor will cut output, not just brightness. To tame some brightness, a capacitor would be the component of choice.

Or, you can just turn down your tone control . . .

boldarrow, you may be overthinking this a bit. I don't think that 500K pots all around will make your single coils too bright.

On a regular Strat, in position 2, you have all three 250K pots in parallel which knocks the combined resistance way down- but position 2 is not noticeably "darker" than position 4, where only 2 pots are in circuit. The same is true on the other end of the scale with higher resistances.

We're largely in a realm of personal taste here.

As farren notes, matched values are not an issue, it's the overall resistance that matters. The higher the pot value, the less variation you get as you turn it down- there's less "sweep" for adjustment. If you were to use a pot with a value of, say 3MΩ for a volume, it would operate more like an on/off switch- all or nothing. But as between 250K and 500K, the difference in sweep as you turn it down isn't likely to be noticeable.

[farren]

Mar 26, 2013 6:40:14 GMT -5 newey said:

A resistor will cut output, not just brightness. To tame some brightness, a capacitor would be the component of choice.

Ahh, so my scheme to learn from someone else's thread worked!

[newey]

farren-

I thought your goal was to knock back the output so as to correct for a pickup mismatch (one "hot" pickup), not a lack of brightness? Apologies if I was wrong about that in your thread.

[sumgai]

newey,

Lack of brightness in his thread, lack of brightness in his head... meh, what's the difference?   So long as we cure at least one of those 'lacks', then our work here is done. ;D




sumgai

[farren]

Mar 26, 2013 16:02:52 GMT -5 newey said:

farren-

I thought your goal was to knock back the output so as to correct for a pickup mismatch (one "hot" pickup), not a lack of brightness? Apologies if I was wrong about that in your thread.

That is my goal in my more recent thread (Norton bridge + X2N neck combo), but I'm primarily concerned with dimming parallel brightness in the 5-way thread. I'm now considering different cap values to use instead of resistors, though I wouldn't mind "pull for resistor/cap" reducing a little bit of brightness and output. I believe that any output that is cut with a resistor will disproportionately be from the high end of the spectrum, though specifically targeting highs with a cap may be a better idea... I'm sure I'll end up testing several solutions, though. As for my thread, though, I brought up the resistor rather than cap, so it was my fault

Mar 26, 2013 17:47:35 GMT -5 sumgai said:

Lack of brightness in his thread, lack of brightness in his head... meh, what's the difference?   So long as we cure at least one of those 'lacks', then our work here is done. ;D

Ouch.

[ashcatlt]

Mar 26, 2013 17:54:53 GMT -5 farren said:

I believe that any output that is cut with a resistor will disproportionately be from the high end of the spectrum...

Yes, way disproportionately. The resistor will have to start to get close to the value of the pickup's internal resistance before you start to notice much broadband volume reduction. By that point you'll be getting little more than luke warm mud out of the thing. Of course, since treble content often fools us into thinking a sound is closer and/or louder, there may be a loss of "percieved" volume, but technically...

[newey]

farren-

First of all, listen to ashcatlt, he's the moderator of this here turf for a reason.

As far as using a cap to trim the highs, nothing new there, Leo's original Esquire wiring in the '50's featured a cap-bleed position on the three-way switch for a "fixed bassy tone", as the description went.

I've used a three-way toggle to do this on my travel guitar, using a .022µf cap with the P90-ish pickup. It gives a "tone control at about 1" tone.

I would suggest first modeling this with different cap sizes. You would need to know your pickup's inductance to do so in a meaningful way, however- and this information is often unavailable unless you can beg/borrow an LCR meter.

In addition to a modeling of it, a cap-substitution box can be set up external to the guitar to test various cap values. You don't even really need a substitution box, you can just test one after another in a serial fashion. But the box allows for, if not strictly an "A/B comparison", at least an "A, then pretty quickly B" comparison.

The Alpha and Omega to this discussion was provided by the late ChrisK with his article on Pickup Coil Response Tuning, which references an article by Helmut Lemme on the subject.

Lemme's article gets to be pretty heavy slogging for those (like me) who lack any detailed electronics knowledge. I certainly don't pretend to understand all of it. But one important take-away was that, by judicious choice of cap values, not-so-significant frequencies could be attenuated, while more sonically useful frequencies could be enhanced. The idea was that, because we hear certain frequencies differentially, one could "tune" the frequency response of a given pickup so as to optimize a certain "sweet spot".

Anyway, if you really want to explore the theory of all of this, Lemme's work will keep you busy for awhile . . .

[ashcatlt]

Absolutely go grab JohnH's GuitarFreak spreadsheet from our Reference Section. You can change the pickup capacitance value to simulate adding a parallel cap, and just change the V pot value to show what happens when you add the parallel resistor.

I believe that what you'll find is that the resistor damps down the resonant peak at the high end without changing the cutoff point, while the capacitor moves the peak without much changing its amplitude.

But that won't really tell you how it sounds. You can test these components outside of the guitar. As long as you leave the V pot on 10, the order of the components don't matter. Use some alligator clips and try it out!

[farren]

I'm continually astounded by the technical information dispensed here when other forums are chiefly concerned with which pickup supposedly complements which fingerboard wood... Looks like I have a bit of reading to do Thanks again!

[sumgai]

farren,

Mar 27, 2013 13:20:37 GMT -5 farren said:

Looks like I have a bit of reading to do

You better pack a pair of pajamas and a toothbrush, 'cause it's gonna be at least an overnight job! ;D

Welcome aboard!




sumgai

[farren]

Thanks!

Having read over many of his materials by now (a cursory glance, admittedly--I'll have a deeper reading when I'm done with the fret and finish work I'm still wrapping up for some of my guitars before I drop in new electronics), may I ask if he is "late" because he left this board never to return when one of his designs was hijacked with no credit initially given, or if something else happened after he left? Not really my business but I'm curious as to if "late" was tongue-in-cheek or more serious. A loss regardless, clearly.

Speaking of hijacking, sorry for stealing your thread, boldarrowoftime. Hopefully your concerns were answered and some of the bonus material was helpful as well

[JohnH]

Thats OK. Chrisk was a key and very clever member of this forum, and sadly, he passed away a few years ago. But we remember him fondly and refer to his posts often.

[farren]

Ahh :/ I suspected it may have been in jest because I read his last several posts after which he took a break from the forum. Sad that the break became permanent for a different reason... But enough of that.

[newey]

Farren-

Here's the relevant thread:

R.I.P. ChrisK

After reading that again, I think I'll go back and sticky it. Sad to let it drop so far down in the coffee shop. The third anniversary of his death was last month.

Chris knew for several years prior to his death that he had terminal brain cancer, and he had undergone several surgeries which were designed only to buy him some time. He had told me about it, in confidence, sometime prior to his leaving the Board, in connection with some legal advice I gave him.

I have always wondered whether his frustration, and ultimate departure from here, in Sept. 2009 were in some way related to his medical problems, since he died less than 6 months later. But, we'll really never know, and I prefer to remember the good times.

So, it wasn't in jest that I said "late". I usually insert that when I'm referring to one of Chris' diagrams or posts, if only to head off inquiries over why Chris can't personally help folks with his diagrams.

But we do miss him indeed.

EDIT: Fixed Link

[farren]

Ahh I'd looked for a bit before but missed that. I always have this expectation that a deceased member will have an edited signature or title or something to denote something has happened, but sometimes those things are left alone out of respect. His karma rating was probably indicative of that, but I wasn't sure... With all those highly regarded posts perhaps it was earned

After reading that thread and the article posted within it, he sounds like exactly the kind of technical-minded musician that is so often missing from most online communities. Knowing his prognosis was terminal for a while, I can only assume someone in such a situation will at some point reflect on the very much finite nature of time as it relates to the short scale of the human experience and re-evaluate how they spend their free hours. Considering how much he'd already contributed to this place and the lasting legacy his posts here have established, one could hardly argue against what may have been a reprioritization of values in the endgame.

By the way, chop off the '&page=' or add a '1' to the end of that link as it currently returns an error. Stickying it would definitely be wise.