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The Fender Telecaster Elite used the TBX tone control, and so a recent discussion suggests understanding what that circuit does.
Fender claims its passive TBX tone control circuit offers features that you might expect to require an active circuit. Fender is bit vague about what it does, but here is a description from a place where you can buy the modification kit:
"Some American Standard Strats are equipped with this tone control to cut either treble or bass instead of the standard style that attenuates treble only. When the control is set at the centered detent, it is off. Turning the control one way cuts treble; the other way cuts bass.”
To summarize the analysis below, a better description of its performance is this: The first thing it does is the first thing a doctor is supposed to do: cause no harm. That is, you do not lose any significant capability, although the response is different with the pot near 0. The second thing it does is to allow somewhat more treble boost than a standard tone circuit, almost as much a tone circuit using a so called “no load” pot where the tone circuit is disconnected at “10”. The third thing it does is to allow good adjustment capability all the way up to the increased treble level. The fourth thing it does is to provide a different taper than you can get with a simple tone control. You might or might not like it; that is subjective and entirely up to the individual.
It does not cut bass, and it is not “off” at the centered detent.
To understand the TBX, it is first necessary to understand the standard tone control circuit. A review follows.
The first attachment shows a simplified guitar circuit. The tone control is the pot and capacitor, but it operates using the pickup coil inductance and all parallel capacitance, including the coil and cable capacitances and stray capacitance. With the tone pot disconnected, the circuit has a resonance, damped so it is broad (low Q). So connect the series pot and cap with the pot on 10, and you damp this resonance a bit. Turn down the pot and you damp it more. Turn it down more and the capacitor becomes important so that with the pot on zero you have a resonance at a lower frequency.
The second attachment is a set of frequency response measurements by Antigua from the guitarnuts2 pickup measurement forum. You see just what I described above.
Does the tone capacitor affect the higher frequency resonance at all? Well, maybe just a very small amount. The magnitude of the impedance of the capacitor at 3KHz is about 2.4K ohms. This is very small compared to the the resistance of the pot, 250 Kohms, and so the capacitor acts almost like a short circuit until the pot is turned almost all the way down. And then the effect is to make a lower frequency resonance as the attachment shows. So the circuit has a different resonant frequency at each end of the pot rotation with variable damping in between. The next post describes the TBX circuit.
Fender claims its passive TBX tone control circuit offers features that you might expect to require an active circuit. Fender is bit vague about what it does, but here is a description from a place where you can buy the modification kit:
"Some American Standard Strats are equipped with this tone control to cut either treble or bass instead of the standard style that attenuates treble only. When the control is set at the centered detent, it is off. Turning the control one way cuts treble; the other way cuts bass.”
To summarize the analysis below, a better description of its performance is this: The first thing it does is the first thing a doctor is supposed to do: cause no harm. That is, you do not lose any significant capability, although the response is different with the pot near 0. The second thing it does is to allow somewhat more treble boost than a standard tone circuit, almost as much a tone circuit using a so called “no load” pot where the tone circuit is disconnected at “10”. The third thing it does is to allow good adjustment capability all the way up to the increased treble level. The fourth thing it does is to provide a different taper than you can get with a simple tone control. You might or might not like it; that is subjective and entirely up to the individual.
It does not cut bass, and it is not “off” at the centered detent.
To understand the TBX, it is first necessary to understand the standard tone control circuit. A review follows.
The first attachment shows a simplified guitar circuit. The tone control is the pot and capacitor, but it operates using the pickup coil inductance and all parallel capacitance, including the coil and cable capacitances and stray capacitance. With the tone pot disconnected, the circuit has a resonance, damped so it is broad (low Q). So connect the series pot and cap with the pot on 10, and you damp this resonance a bit. Turn down the pot and you damp it more. Turn it down more and the capacitor becomes important so that with the pot on zero you have a resonance at a lower frequency.
The second attachment is a set of frequency response measurements by Antigua from the guitarnuts2 pickup measurement forum. You see just what I described above.
Does the tone capacitor affect the higher frequency resonance at all? Well, maybe just a very small amount. The magnitude of the impedance of the capacitor at 3KHz is about 2.4K ohms. This is very small compared to the the resistance of the pot, 250 Kohms, and so the capacitor acts almost like a short circuit until the pot is turned almost all the way down. And then the effect is to make a lower frequency resonance as the attachment shows. So the circuit has a different resonant frequency at each end of the pot rotation with variable damping in between. The next post describes the TBX circuit.
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