The Fender TBX:
A Cool 2-Band Tone Control

You can TELL it's Photoshopped! There's no TBX!

You can TELL it’s Photoshopped! There’s no TBX!

Thanks again to everyone who chimed in on the “What your favorite mod?” discussion. I got tons of great ideas from your comments.

Like this one, which I’ve been meaning to explore for ages: the Fender TBX tone control circuit, which appears in several Custom Shop instruments, notably the Clapton signature Strats. Like the G&L PTB circuit I’m so apeshit about, it’s a 2-band passive tone control — but one that sounds very different.

The PTB is a two-knob circuit that lets you siphon off highs, lows, or both. I’m agog at how well it works with humbuckers — you can get so many cool sounds by rolling off lows on the way to a fuzz, as heard here.

But TBX (it stand for “treble bass expander”) is a one-knob circuit, tbough that single knob rotates two stacked pots. The control has a center detente. Set here, it’s like a regular tone control, wide-open. Turn it counter-clockwise and highs vanish, per usual. (You could “tune” the roll-off frequency with various capacitors, though I went with the stock .022uF.) But when you rotate clockwise, the absence of lows makes glassy highs erupt.

The dual pot cut highs or lows.

The dual pot cut highs or lows.

Technically, it’s not a boost, but it sure feels like one. Dirk Wacker, my now-colleague at Premier Guitar, dissects the circuit far more capably than I can here. (And he goes way beyond in this subsequent article on TBX mods. Man, I have some catching up to do!) He makes a good case for replacing the stock resistor with another value, but I went with the original 82K to establish a point of reference. I’ll try his mod when I restring, and I’ll update you here.)

BTW, you need the Fender TBX kit for this project — it uses highly customized pots to work its magic, and a standard stacked pot won’t do. But it’s cheap: You can find the TBX kit, with the pot, hardware, and passive components, online for about $15.

I put it into the mongrel strat I’ve been using as my digital synth/looping guitar. I’d been using a Stellartone Tone Styler, a cool Vari-Tone variant that switches between multiple capacitors. I dig it, but it’s the old model which clicks, rather than fades, from setting to setting, and it requires a powerful twist of the wrist to go from maximum to minumum, which I do every time I grab an EBow. Since I hadn’t gotten around to replacing it with the smooth-action version, I figured I’d try the TBX.

And I’m glad I did. It’s a super-easy install, at least to the extent that any job that requires removing both strings and pickguard can be easy.And here’s how it sounds:

I’m going to keep this one around for awhile. You’re hearing it through an analog rig, obviously, but I want to find out whether that extra shot of highs does anything meaningful when playing digitally. I’d also like to experiment with different cap and resistor values.

And now I can’t help wondering whether this would sound cool with humbuckers. Anyone have any experience with that?

27 comments to The Fender TBX:
A Cool 2-Band Tone Control

  • Willverine

    I gave the Wacker passive mod a try in the Epiphone Les Paul bass (loaded with Hagstrom bass humbuckers) just because…meh…might try them in some of my other guitars…so many mods so little solder…

  • thomas4th

    Very cool. I’d like to hear it with humbuckers as well – you’d think the bass cut option would be very useful with them. I have an idea floating in my head for a twin-humbucker guitar with a TBX for each pickup and a phase switch (I’d use a master volume, but you could easily use it in a Les Paul-type wiring; might be control overload with the Pagey Phase 2 wiring!); I’m interested to see what kind of effect the treble or bass cuts would have on the pickups’ interactions out of phase. Like you, I enjoy weird spiky/squawky guitar sounds. They catch the ear and have a ton of personality – the kind of sounds that can really make a tune pop. 🙂 I bet cutting the low end on the neck pickup would be pretty useful for funk/reggae-type chord stabs.

    An odd place I’ve seen the TBX pop up is on Duff McKagan’s signature Precision Bass. Unusual to see a bass cut control on a bass guitar (at least a passive one, anyway).

    And hey, that’s a pretty slick Guild (?) bass hiding in the corner there! I can’t recall having seen it before.

    • joe

      Yes — there’s something missing in my studio: I moved the piano out, so you can see some of the other guitar. That bass is a ’60s Guild Starfire that I keep strung with tape-wounds for a faux-upright sound. I once got to hear it alongside Justin Meldal-Johnsen’s reissue Guild Starfire — and the reissue sounded way better.:)

  • George Anthony Harvey

    I have an early ’90s American Standard Strat that came stock with the TBX (bridge pickup only) that’s almost always in center-detent position. I never appreciated the subtle nuances before, but now I have some fresh ears. So, thanks.

  • Bryan

    Hey Joe! Great blog post. I have an early 1990s dual humbucker guitar with a factory-installed TBX control. Mine has a .022uF cap and 82k resistor, plus a 4.7M ohm resistor wired in parallel with the capacitor. I believe that Fender installed this second resistor on their TBX-equipped basses, too.

    Wired this way, there is no apparent bass cut when the knob is turned clockwise past the detent, at least to my ears. It sounds more like a treble-mid boost. Now I’m tempted to mod the circuit to provide more of a bass rolloff effect.

    Speaking of bass rolloff, have you tried the Bass Contour circuit used by Reverend Guitars?

  • Oinkus

    Still have one in my box of stuff tobeused,only experience I have is with one I gave to a friend. He loves it in his Stellacaster. I still have 2 builds in the works and both have humbuckers, so it is possible it could make the call. What I really would like to try that with is some P 90s ?

  • Hernan

    Hello Joe, great tone and playing as usual. What are the chords that you are playing at the beginning?

    I think I had this circuit in a Telecaster in the ’90s, but I was completely clueless as to its inner workings. I think I just used to leave it parked on the center detente. :shake:

    • joe

      Hiya Hernan — I’m tuned to dropped-D, like I am 80% of the time. When I tune that way, I use a lot of “D shaped” barre chords, rather an E- or A-shaped ones. So the progression is sort of E/D/G/A, with a lot added notes, just based on open strings and pull-offs. Maybe you could call it E7/D6/G(#11)/Aadd9?

  • My only encounter with the TBX was in a couple of American Standard Strats friends had over 20 years ago. Didn’t like it then, but my ears and methods are quite different now. The vid definitely makes me consider revisiting.

    Could be fun in an Esquire with the switch repurposed for a coil-tapped bridge pickup like some of the ones Duncan and Don Mare offer.

    • joe

      I’ve had Esquires on the brain lately. I’ve never owned one — I’m not even sure I’ve ever played one! (Seymour Duncan owns Jeff Beck’s Yardbirds Esquire, though I’ve only seen pictures of it.) But I’m real curious about what you could do with a single pickup and some tricky wiring….

      • bear

        Same boat on Esquires–fascinated but no encounters. For a parts build, the obvious bonus is you only need to fund one good pickup to get going and you get all sorts of fun wiring experiments. (Just two screws to remove and you don’t even have to loosen the strings–must be why Tele and Esquire players seem to do more wiring mods than players of other guitars.)

  • Sebastian Enriquez

    Joe, what happened to your piano?!

    Cool mod; maybe I’ll try it in my Booster-Strat,just to hear how it sounds.

  • Freddie Lentzell

    You say you need “highly customised pots” for this, but the fact that the kit is so cheap started me thinking. If I’m not missing something, what we have is a dual ganged pot 1M + 250 K. You probably won’t find that at Radio Shack (I’m extrapolating, there’s no Radio Shack in Spain), BUT if you put a 330K resistor across one of the halves of a 1M dual pot, what you get is a 250K pot along with the original 1M, that is, the higly customised pot.
    I might be wrong, but if the pot has no other special characteristic (antilog or something, I haven’t found enough info yet), this a very old trick and very useful here.
    By the way, before I forget again, how can I change my avatar for posting?

    • Freddie Lentzell

      Well no, it seems I was wrong. The 250K side (treble cut) does nothing from mid position onwards, whereas the 1M (bass cut) does nothing until it reaches the mid position. A highly customised pot it is, then. Live and learn.

      • joe

        I probably would have tried the same thing, had I not read the Dirk Wacker column I linked to in the post. He does a good job of explaining why the pot is so unique.

  • Well I dunno, I have had one of these (yes with the Fender pot) in one of my self built Tele’s and I have always been totally underwhelmed by it. Mine seems to work much like a normal tone control. I don’t normally screw up guitar control wiring jobs and if I remember rightly I double checked it when I was initially not impressed.

    I guess I’ll have to check the circuit diagram and the wiring and the pot to see if I screwed it up. Or maybe I’m just not listening for the right thing.

  • Roger

    I have been in the proccess of moving my studio lately so I don’t have access to this guitar, but here is a pic of a inexpensive Squier I was using to test the TBX out. I do looping stuff as well, and I find that cutting the lows is very useful when layering multiple loops. Anyway, I had this little breadboard that I stuck on the guitar so I could try different caps out. Really, I can’t wait to get my gear back up and running so I can play around with it.

  • Anyone know if Godin’s HDR/High Definition Revoicer circuit is similar to the treble-expander part of the TBX, but with a fixed value? It would make sense on the level of switching on an active-ish sounding boost and enhanced high-end detail in a passive circuit.

  • James

    I’m nearly finished building my Baritone guitar (waiting for the finish to cure) that I’m putting not one, but 2 TBX circuits. It has a “dirty fingers” humbucker in the neck and a 500t in the bridge. Each pickup is split and each coil is run to its own volume. From there each pair will be sent to the TBX. I’m hoping to be able to pull off playing a guitar and bass at the same time by simply flipping the switch between each pickup into my looper.

    But in the mean time I started wondering what effect the TBX would have in a wah-wah pedal. Any thoughts? Ever done this?

    • joe

      Wow, James — sound super-cool. I’ve never tried that particular arrangement. I’d love to hear some audio when you’re done. Now have I ever tried combining the TBX with away. I await your report. 🙂

      I’m aways fiddling with the guitar/bass/looper. For me it’s sometimes as simple as tuning low and playing bass with a soft, bare-finger using the neck pickup.

  • davo

    Ive had this circuit in my P90 equipped PRS for over a year and I have to say this modded TBS circuit is MADE for P90’s.

    It can truly cover the spectrum from humbucker territory into classic fender cleans. Slight mods to the circuit (I used a capacitor socket to swap values) can adjust the frequency of the bass cut as well as the frequency and sweep of the standard tone settings.

    Its a massive upgrade for just a few bucks.

  • davo

    Yes, TBX. As you noted, Dirk Wacker mentioned it a bit.
    It more than any other mod Ive tried allows a good p90 to cover most electric territory, and it does it with only one pot, while also maintaining a traditional tone contol fxn (no load, even) but adds much more at the same time.

    The other p90 mod I have found exceedingly useful is switchable standard/50’s wiring. It allows those great standard p90 tones (that get a bit dark if you turn your volume down to clean up-but that overdrive an amp so well), but also allows more presence and cleans up with more clarity when set to 50’s.

    I install the switch as a push/pull volume pot. Its actually quite nice to have both options-the difference is significant. I do it to my teles as well.

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