Guitar tone control secrets...

[Steve A.]

Chuck H. made a post on a recent thread regarding a passive mid boost/cut control that enlightened me to hidden features of the traditional treble cut tone control on guitars. It always seemed to me that turning down the tone control on a guitar just cut back on the treble, making the sound very muddy when set to 0. Handy to use if your amp settings were too bright but I'd rather adjust the tone at the amp and leave the guitar tone controls set to 10.

Yes, passive can only attenuate sound, so itīs reasonable to use them in attenuating some "ugly" frequency. When trying to "boost" anything, it only means "attenuate everything else".

Well, not exactly... there is a circumstance in this [mid boost/cut] circuit's implementation that wasn't considered in your response. And that's the resonant peak frequency. It's the reason the "tone control all the way down" tone works for neck humbuckers. It cuts treble, yes, but it also lowers the resonant peak of the overall circuit and there is an actual boost to other midrange frequencies. Remember that the pickup is an inductive element.

The only time I ever noticed that was with the .015uF "Eric Clapton woman tone" cap used with a SD '59 neck pickup... turned down to 0 it had a definite "Sunshine of Your Love" sound to it. But other than that I have never noticed anything but muddiness when turning a guitar tone control all of the way down.

It so happens that when I read Chuck's post the guitar I have been playing lately has been a PRS SE Custom Semi-Hollow fitted with TV Jones Classic and Classic Plus pickups. "Hot damn... doing that opens up all sorts of new sounds!" Turning the tone control down to 0 and then raising it a little produced a much fuller sound with lots of lower mids. And it had similar results on the bridge pickup as well.

After tripping out on that for several days I decided to try that trick with a 2016 LP Tribute with Burstbucker Pros and there was nothing but muddiness as I turned down the tone controls. No hidden magic in there at all!

Chuck's post mentioned inductance so I thought I better check the specs. The TV Jones Classic and Classic Plus pickups have, respectively, a DC resistance and impedance of 4.8K/1.83H & 7.8K/2.83H. The Burstbucker Pros have a DC resistance around 8K but I could not find the inductance, only I did find an article mentioned that PAF style humbuckers generally have an inductance between 3.2H and 4.6H.

I tried the same experiment with a Gretsch G5438 Electromatic Jet with Black Top Filter’Tron™ humbuckers and the results were similar to the TV Jones 1959 filter'tron copies. BTW that Gretsch has a wide pallet of tones with the two non-interactive volume controls which allow for a full range of blends in the middle position between 100% neck and 100% bridge. I am starting to appreciate why Gretsch has had so many fans over the years...

FWIW the G5438 uses a .047uF tone cap as I recall when I peaked inside the control compartment. Since neither volume control can mute the output completely there is a master volume control to which I really should add a cap to retain highs as it is turned down (I think that Gretsch is using a .047uF on the master volume controls on the newer models... the G5438 without the Bigsby has been discontinued which makes it an even better deal. I took home 4 different Gretschs before deciding to keep that one. It has a chambered body which makes it light and resonant.)

Steve A.

P.S. So what is the formula for determining the resonant peak frequency of a pickup with respect to the measured values of the tone control circuit?

[Tone Meister]

Another consideration is value of the tone pot itself. The taper of the rolloff is affected slightly between values as well as the knee frequency. For single coils, I typically use .022 for the bridge, sometimes .033 but never larger. Almost always the pots will be the standard 250K.

BUT, with humbuckers, using a 250K tone pot instead of a 500K or 1MEG, the taper will be more gradual, which I prefer, and the knee frequency shifts slightly. Depending on the humbucker, I'll mix and match the tone pot value with the tone cap value to get the amount of treble cut and taper that suits me. As a variable, the inductance does seem to be a significant contributor, IME. I have a Strat with the TV Jones Classic/Classic Plus and that guitar has a 500K volume pot and a 250 tone pots with a .022 tone cap for the bridge and a .015 for the neck. To me, the filter and taper are perfect.

[Mark Hammer]

I use a trick I got from Craig Anderton - a bidirectional tone control. I use a 1meg linear pot, wit the wiper tied to the Volume pot input, and each of the outside lugs tied to a different value treble-bleed cap to ground. One goes to something in the 15-22nf vicinity, and the other goes to something in the 3n3 to 6n8 vicinity.

Why 1meg? Because when the pot is set to mid-point, it is essentially two 500k resistances to ground in parallel. Less than 1meg in this configuration, and you're bleeding treble from the get go. Rotate the pot from the mid-point in one direction and you get the traditional "dulling". Rotate it the other way and you get two things: first it kind of sands off the edges, while keeping mid-range bite, and second, it shifts the resonant frequency down a bit, but not too much. Great for making a single coil sound vaguely HB-ish. The other nice thing is that since it "compresses" the full range of adjustment into half the pot's rotation, that makes it easier to do "pinky wah", assuming your pinky can reach the knob from a playing position. Naturally, this works best on a master-tone control guitar. The only caveat is that I can't seem to find an inexpensive 1meg linear with a centre-detente.

[bbsailor]

I use a trick I got from Craig Anderton - a bidirectional tone control. I use a 1meg linear pot, wit the wiper tied to the Volume pot input, and each of the outside lugs tied to a different value treble-bleed cap to ground. One goes to something in the 15-22nf vicinity, and the other goes to something in the 3n3 to 6n8 vicinity.

Why 1meg? Because when the pot is set to mid-point, it is essentially two 500k resistances to ground in parallel. Less than 1meg in this configuration, and you're bleeding treble from the get go. Rotate the pot from the mid-point in one direction and you get the traditional "dulling". Rotate it the other way and you get two things: first it kind of sands off the edges, while keeping mid-range bite, and second, it shifts the resonant frequency down a bit, but not too much. Great for making a single coil sound vaguely HB-ish. The other nice thing is that since it "compresses" the full range of adjustment into half the pot's rotation, that makes it easier to do "pinky wah", assuming your pinky can reach the knob from a playing position. Naturally, this works best on a master-tone control guitar. The only caveat is that I can't seem to find an inexpensive 1meg linear with a centre-detente.

Mark,

There is another way to get dual sounds with much more common parts. Obtain a 500 K pot with a push-pull switch and then switch between the two capacitor values.

Joseph J. Rogowski

[rjb]

There is another way to get dual sounds with much more common parts. Obtain a 500 K pot with a push-pull switch and then switch between the two capacitor values.

Of course Mark's method doesn't require a center-detent pot. Just use a knob with a pointer. Or "earball" the center position.

-rb

[Leo_Gnardo]

Or "earball" the center position.

Yusss! .... deserves a thumbsup

[Steve A.]

Thanks! After reading all of your suggestions so far I took the liberty of renaming the thread to accommodate multiple secrets...

FWIW I normally prefer linear taper volume pots because I like the added precision when turning down from 10... I have never once had a vocalist yell at me to turn up my guitar! It worked out great with PRS SE guitars which usually come with single linear taper tone and audio taper volume pots as I could just swap them around. (I very rarely turned down the tone controls on my guitars until last week so the taper was not exactly very critical to me.)

When wanting to increase the value of a tone cap for a too bright bridge pickup adding a .01uF cap to a stock .022uF cap can work and blending different types of caps can have interesting results. And on a guitar with a single tone control you can add a cap in series with a 270k or 510k resistor directly to the selector switch to cut the brightness in the bridge and blend positions.

Interesting but true... my 1937 Rickenbacher Silver Hawaiian lap steel has a single pot — a volume control wired as a two terminal variable resistor. You'd think that the lack of a tone control would create problems but as you'd turn it up from 0 the sound got progressively brighter so the single control served both functions to some extent, at least with the horseshoe magnet pickup. (I had the hots for a bakelite Rickenbacher like David Lindley's so I stuffed the hollow metal body with red and white shop rags from Harbor Freight and Ace Hardware until I got the desired tone cutting down on the hollow resonance which took a little mechanical "recalibration" removing excess rags.)

For your daily fix of eye candy...




Steve A.


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[Steve A.]

Of course Mark's method doesn't require a center-detent pot. Just use a knob with a pointer. Or "earball" the center position.

-rb

If you have a spare Fender TBX control around it has a center detent with one gang 250k and the other 1M. I read about rewiring one for treble cut in one direction and bass cut in the other but had trouble locating the actual circuit diagram... anybody here have it?

Here is the TBX rewire for passive pickups that Doc came up with at AMPAGE back in 2001. (The stock wiring has an 82k resistor to ground from 0 to 5 designed for the mid boost board but kills highs with passive pickups.) I had come up with a similar drawing but Doc found that the control worked more smoothly with the 220k resistor he added between the two gangs so he gets the credit for the mod while I was just the damned librarian...

Just kidding... Doc was a major contributor at AMPAGE. One thing I learned from him was when cutting nut slots deeper make sure that they slope down towards the headstock a bit to avoid the sitar or banjo effect. I talked to him maybe 10 years ago at which time he had no internet other than at the public library...



http://www.blueguitar.org/new/schem/_gtr/tbx_mod.zip

Steve A.

[rjb]

...I stuffed the hollow metal body with red and white shop rags from Harbor Freight and Ace Hardware until I got the desired tone....

So that's my problem! I was using blue shop towels!

-rb

[Mark Hammer]

True. I find that shrinking the arc of rotation by half brings its own conveniences which, understandably may not hold the appeal to others that they hold to me. And while I am aware how much folks like the idea of push-pull pots, after trying to live with one on my Parker guitar, I find them disruptive That said, for those instances where one would rather not sink another hole into a guitar or clutter up the control area, push-pull pots are a godsend. The bidirectional control doesn't require any cosmetic changes to the instrument either. Six of one; half dozen of the other, eh?

[Steve A.]

So that's my problem! I was using blue shop towels!

-rb

Seriously, the density of the red and white shop towels were quite different. And while it was really easy to shove the towels up the hollow neck it was a real bear to pull the excess ones out!

Steve A.

[Steve A.]

True. I find that shrinking the arc of rotation by half brings its own conveniences which, understandably may not hold the appeal to others that they hold to me. And while I am aware how much folks like the idea of push-pull pots, after trying to live with one on my Parker guitar, I find them disruptive That said, for those instances where one would rather not sink another hole into a guitar or clutter up the control area, push-pull pots are a godsend. The bidirectional control doesn't require any cosmetic changes to the instrument either. Six of one; half dozen of the other, eh?

Well, Mark, have you looked into push-push pots? They are much easier to operate. A Parker Fly?!? I didn't realize that anyone still played them... I don't like ss frets - to my ears they click. Jescar EVO is the gold standard for me...

Steve A.

[bbsailor]

All you members tinkering with tone control look at this.
The Electronic Goldmine has a sale now until June 21 for dual audio taper 500 K ohm pots for $2.99 for a package of 4 pieces. Part number G22886.

Audio taper resents a 10/90 percent split at half rotation and a 50/50 percent split at about 70 percent rotation. Since dual capacitors may have a value difference of about 4 or 5 to 1, you may be able to creatively use these dual pots to achieve some interesting tone control variations different from traditional methods.

Joseph J. Rogowski