After reading lots of differing & conflicting explanations of how the Fender TBX tone control works, I decided to take apart my Strat & find out. This is a '94 Strat Plus with Lace sensors. I don't know if there are variations of the TBX. I desoldered the resistor & cap so that I could get accuarate measurements.

So, here's the deal. It looks like a double stack pot with 1 shaft (not dual concentric), but the pots are NOT standard pots by any definition. There is a detent position at the center of the pots' rotation. Fender only uses pins 2 & 3 of the pots (the wiper & the terminal on the clockwise end of the pot). I think it's best to think of these pots as 3 separate functions - 0-5 on the knob, the detent postion in the middle, and 5-10 on the knob.

Measuring between pins 2 & 3, the bottom pot (with the shaft up) is a standard 250K audio taper pot from 0-5 on the knob (CCW end to just before the detent position). At the detent position, it goes open (like a no load tone pot). From 5-10 on the knob (the detent position to the CW end), it remains open & out of the circuit.

Measuring between pins 2 & 3, the top pot (with the shaft up) is a 0 ohm connection from 0-5 on the knob (basically a solid wire connecting the pins). At the detent, it remains 0 ohms. After the detent from 5-10 on the knob, it is a 1M ohm linear pot.

I've made 3 schematics of the 3 phases of the tone control.

0-5 on the knob before the detent, it looks like a standard Fender tone control circuit with an 82k resistor added to ground:






At the detent position, the standard tone control is removed from the circuit due to the bottom pot going open at the detent, but the 82K resistor to ground (in parallel with the pickup(s)) stays:






5-10 on the knob after the detent, the 1M linear pot comes into the circuit in series with that 82k resistor. As you turn the knob, the added resistance reduces the effect of that resistor's load on the pickup(s) until at 1M, it has almost no effect. I found that removinging the TBX control (with a switch) did provide a little more brightness than even the full CW setting of the TBX, though.





I find that I usually like the TBX set at just beyond the detent (6 on the knob), so I might try increasing that 82K resistor a little.

Here's a pic of the TBX layout.

I made a video of this:

http://www.youtube.com/watch?v=gFcr1ckSlDE

That is a wonderful analysis! Thanks for posting it.

My original posts show the 1M pot as a linear taper pot. It's more of a custom log taper.

What's cool about the TBX pot is that it is (almost) perfectly setup to be wired for treble cut, no load, and bass cut with one knob. I don't know why Fender never wired it that way. I've put the modded TBX in two 2 humbucker guitars and it works really well to thin the humbuckers when you want to.

I don't know if I've ever posted that mod on this forum.

Here's the wiring diagram to modify the TBX pot setup so that you can get both treble cut and bass cut with a no load position in the center.

I just installed a TBX tone control in my MIM P-bass, as an experiment.

The Precision Elite I (1983) had a TBX tone control together with a preamp. But that gives to much high frequencies.

What I hear so far, is that the MIM P with TBX has more precence (5 -10).

Because I installed it in a bass, I am not going to try the modification Phostenix/

Tomorrow I will use the bass in a live situation and let you know if/how it worked.

Suggest you check out archives in Premier Guitar magazine as well. They did a piece on the TBX this year. Interestingly enough, on another thread currently running, Chromeface reitterates that Clapton had the TBX pulled from his stage guitars and replaced it with a conventional tone pot, having considered the TBX tone 'too mushy'.

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"Another day in paradise!"

I've read that before. There are quite a few statements that I disagree with in it, including the idea that (wired the way fender typically wires it) the TBX control is a bass cut circuit from the center detent to full clockwise. The TBX is also NOT a no load tone control the way Fender typically wires it. There is that 82K resistor loading your pickup(s) in the center detent position. The 2nd half of travel doesn't give you actual bass cut, but increases the resistance that is loading the pickup(s) until it is over 1M at the full clockwise position. So, the TBX approaches no load at fully CW, but it is never a true high pass filter that cuts bass frequencies.



The above quote is simply not true of either my 1994 TBX control or the new ones I've recently purcahsed. I would describe it as a modified 1 Meg log pot. My youtube video explains this more fully.

And, when people start suggesting that I should get NOS carbon comp resistors to reduce noise, I stop listening to them.


These types of articles are why I finally took a couple of them apart to find out how they really work & came up with the mod to get real bass cut from the 2nd half of the control. I do like the way he wired the modified version that gets treble & bass cut capabilities, though.

BTW, I made a followup video when I checked the TBX control from my 94 Strat.

http://www.youtube.com/watch?v=E1rbDOcRp50

After all is said and done, are you of the opinion that your reworking of the circuit yields more bang for the buck, so to speak, than just swapping it out for a standard tone pot?

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"Another day in paradise!"

Thanks for this post, my brother...this is the kind of stuff I was talking about in my (too) lengthy "Remember When" thread.

Very cool info--how to mod what was originally itself a mod...

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Good Vibes To Y'all!



Screamin' Armadillos
Texas Roadhouse Music
Guitar/Slide Guitar/Harp/Vocals

+1

Dude, That's awesome and your vids are great! 50 points to you sir!

Andy

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Pending Greatness

If you already have a TBX & you want it to be a little brighter at the mid-point, you can increase that 82K resistor that loads the pups. Some people go up to the 150K-180K range and some people go up to 220K so that the center detent position is similar to a standard tone pot turned all the way up. Then, from center to fully clockwise it goes progressively no load. At fully CW, it's not actually no load, but it's close enough (1.22M ohms in parallel with the pickup(s)).

Using the 220K resistor instead of the stock 82K is usually referred to as the Doc Mod - http://www.fenderforum.com/forum.html?d ... 9&offset=0
With their mod, Doc & Steve Ahola were looking to brighten up the mid point & still maintain a smooth transistion to "no load". They didn't like the change to no load that you get with a Fender Delta No Load pot.

I actually don't mind the jump in brightness with you flip a no load pot up full, so I would go with a no load pot if all I wanted was full brightness from my pickups.

What I was trying to acheive with a TBX control was to actually have bass cut from center to fully CW. I find this incredibly useful with humbuckers to thin them out when I want (especially the neck) without splitting them & losing their hum cancelling capabilities. I've got it in 2 HH guitars now & I love it.

The other use I had in mind is for Strats & Tele with pickups in series. Some people think the Tele pups in series tone is too fat & pickups in series on a Strat tends to be kinda muddy - especially Neck & Middle in series. I will be putting a modded TBX in my Strat soon with my Strat-X wiring setup that has all 3 in-series options, so we'll see how well the Modded TBX works for that.

It's also great for lo-fi tones.

Thanks guys. I hope to make some demo videos soon so that people can hear some of this stuff. I'm also working on a website to store the library of drawings I've got....

very interesting post, muchos gracias!

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