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Versatile Telecaster Controls
By Sid of Stone Marmot
Nov. 28, 2008
My Telecaster is a 1990 American Standard that originally had the TBX tone control. A lot of people don't like this tone control. I myself never really minded it since I rarely use my tone controls on my guitars. But, on examining the way the TBX control itself works, I discovered you can do something with it that you can't do with almost any other control.
All the passive tone controls, that is, tone controls that don't have active electronics that require batteries or some other power source, I have ever seen on a guitar vary the tone by cutting the highs. But sometimes it would be nice to cut the bass. With proper wiring of the TBX tone control, you can use one control to cut the highs and cut the bass, though not at the same time.
I don't know if all TBX controls work the same, but mine works as follows: The lower potentiometer varies from 0 Ohms full counterclockwise (CCW) to about 250 kohms just short of the midpoint, which has an indent you can feel, beyond which it is open circuit. This means that, if wired correctly, it can work like a standard Tele tone control except it provides the full standard Tele tone control range in half the tone control travel and beyond that point it is open circuit, meaning the tone control circuit is no longer loading the pickups, giving you a little more highs. The top potentiometer is approximately zero Ohms from full CCW to the midpoint (mine actually varies from 0 to 1.7k, which is negligible for what I'll discuss later), beyond which it varies from approximately 0 to 1 Megohms.
Figure 1 shows the schematic for how I modified my Telecaster, with the exception that I used a five position Stratocaster switch instead of a four position switch (S2a and S2b in the schematic) in place of the standard three position Telecaster pickup selector switch. I used the Strat switch only because I had one in my parts drawer. A four position switch is better as two of the positions on my Strat switch are redundant. In a future article on this blog I'll show how to use a Strat switch for those who may be interested.
Figure 1 - Schematic For Telecaster With Versatile Controls Built Around TBX Tone Control
As you can see from the schematic, this circuit gives you four pickup selections: The standard three Tele selections, bridge, neck, or both pickups in parallel, and a fourth selection, both pickups in series. This has been discussed in many places and instructions for this mod are included with the Fender 4-way pickup selector switch (model no. 099-2250-000). Figure 2 shows a drawing of the back view of the switch to indicate how I define the terminal numbers. It doesn't matter if the metal side of the switch is up or down in this drawing as the switch is symmetric. If you want your pickup selection positions to be similar to a standard Tele, your switch should be mounted so that S2a-1 and S2b-1 are closest to the volume control.
Figure 2 - Pinout Designations For Fender 4-Way Pickup Selector Switch
The schematic also shows a second switch is added, a standard double pole-double throw (DPDT) toggle switch. This second switch reverses the phase of the pickups when both are selected, which has also been discussed and done many times before. This requires the only modification you have to make to the control mounting plate: A small hole, usually ¼ inch diameter, to mount the switch. Figure 3 shows how I added mine between my volume and tone controls. For mine, in phase is when the switch handle is in towards the pickups, out of phase is when the switch is out away from the pickups. You don't need to add this switch if you don't want this feature or are reluctant to modify your mounting plate (though replacement Tele control mounting plates are readily available and fairly inexpensive). Just wire the neck pickup as if the switch were always in the “In phase” (no. 2) position.
Figure 3 - My Telecaster Controls Showing The Added Phase Switch
I bypassed the volume control R1 with a 510 pF capacitor C3. For most guitars, some highs are lost as you turn down the volume control. C3 is supposed to compensate for this effect. You can leave this cap out if you don't care for this feature. You can also adjust the value of this cap to better compensate for your tastes, with a larger value giving more highs and a smaller value less highs. Some people also put a resistor in series with this cap to smooth out this compensation as the volume is reduced. 100K to 150k are typical values used for this series resistor, if used. Again, adjust to taste. Again, all this has been done and discussed many times before.
Now we come to the unique portion of this schematic, the tone control R2. The bottom half of R2, R2b, with C1 looks like your standard Tele tone control circuit. But since it is a TBX control, it varies the tone for only the bottom half (full CCW to middle) of the tone control travel, beyond which it is open circuit and disconnected from the rest of the electronics. The big difference is C2, which is in series between the pickups and the volume control, and the top half of the TBX tone control, R2a, which is across C2. C2, in conjunction with the impedance of the pickups and R1, filters out the bass. But for the lower half of the tone control range, R2a is effectively zero Ohms, shorting out C2. So C2 has no effect for the lower half of the control range. But beyond the midpoint of the tone control range, R2a starts getting bigger, with less signal going around C2 and more through C2, cutting more and more bass as the control is turned up to full clockwise. Of course, the value of C2 can be adjusted to taste.
This is effectively the same as the bridge pickup on many Rickenbacker guitars, which have a similar capacitor in series with that pickup. This is one reason for the characteristic bright jangly sound of a Rick (but only one reason. If you really want to sound like a Rick, get a Rick. I did.) But on the Ricks, there is no potentiometer shunting the cap, so the bass is cut all the time for that pickup. Here it is adjustable.
Figure 4 shows the back side of the control plate with this mod. Remember that I have a 5-way Strat switch in my Tele, not the 4-way switch. Note that the TBX tone control is rather tall. I measure mine as 1.0 inches from the bottom of the control plate to the bottom of the tone control. If you are putting this mod in an instrument that doesn't already have a TBX tone control, make sure you have enough room. Also note that all these parts do make it a rather tight fit for the Tele control cavity.
Figure 4 - Back View Of My Modified Telecaster Controls
To my knowledge, this can only be done with a single control with the Fender TBX tone controls. I suspect these TBX controls are custom made for Fender. I can't see much other commercial use for controls with such unusual characteristics.
You can use two separate controls for R2a and R2b. But if you adjust both at the same time, you will be filtering the lower and higher extremes of the frequency spectrum, leaving a strong midrange hump. To my ears that sounds terrible, but others may think otherwise. You also need room for the extra tone control.
This circuit can also be adapted to most any other guitar, including Ricks. I've only tried it on my Tele, since it came with a TBX tone control. Strats with TBX tone controls would also be good candidates for this mod. Fender did, and may still, sell the TBX controls as separate parts. If anyone tries this mod with another instrument, let all of us know. Especially, give us a link to your mods in the comments.
Some may question why do this, since you can usually better adjust the tone at the amp. That is my feeling with all instrument tone controls, which is why I seldom use them. But sometimes these unwanted frequencies can affect your electronics before the tone controls of your amp. This is particularly true if you use pedals, such as compressors, distortions, overdrives, etc. For example, you may adjust your amp for a very bright sound, but you find the bass out of your guitar is pumping your compressor in an undesirable way. This control can fix that problem. Bass is often a problem with distortions, also, muddying them up. This control can fix that problem, too.
So if you have a TBX control, try this mod. Let all of us know if you think you have found better component values for any portion of this circuit.
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