The electronics inside a passive guitar are fascinating. Compared to all the other pieces of modern technology we carry around and use every day, guitar circuits are very primitive. Yet often, it is their simplicity that bares some of the most intriguing complications.
The ProblemAllow me to explain one such complication here. Passive electric guitars (any guitar that doesn't require a battery) use wiper potentiometers to act as what we know as the volume knob. The function of this potentiometer is simple. When at ten, all of the signal from the pickup is being sent to the output of the guitar. When at zero, all of the signal is being sent to ground. The complication arises when you realize that this wiper pot does more than just reduce the perceived volume of the guitar. As you turn the volume down on your guitar, the volume potentiometer begins to act as a resistor in the circuit, reducing the level of high frequencies being sent to the output at a faster rate than it reduces the level of low frequencies. The result is that as you roll your volume down, the tone of your guitar darkens.
Many guitarists (myself included) do not actually have much of a problem with this. For the most part this problem is not unbearable, and it can actually be somewhat interesting and lead to the discovery of some pretty great tones. That said, enough guitarists have been frustrated with this problem over the years that there are well known ways of addressing it known as "Treble Bleed Circuits".
Is There Really A Solution?The only really legitimate way to reduce the level of volume in your guitar without affecting the overall tone is with an active circuit. While many guitarists and manufacturers of passive guitars and guitar electronics have used treble bleed circuits for years, this is really less of a complete "fix" and more of a compromise.
Treble bleed circuits are not so much a solution but rather a compromise mainly because several factors will greatly affect the consistency and performance of these circuits. Namely, the amplifier you are using, the length of your instrument cable, and crucially the components of the treble bleed circuit will have a large impact on how the treble bleed functions.
Additionally, there are three popular ways of wiring a treble bleed circuit and each approach will yield different results.
The Three Treble Bleed Circuits
All you will really need to attempt to wire a treble bleed circuit into your guitar is a soldering iron and some free time. If you're like me and you're not the most confident at soldering then I would recommend not buying the cheapest option, because those can take more skill to use effectively. Something like this would work very well:
The most simple type of treble bleed circuit involves wiring a capacitor in between the input and output lugs of your volume potentiometer.
This type of circuit has been used by guitar manufacturers such as G&L and PRS in the past. It was originally made popular by Fender in the 1960's. Fender used 1000 pF capacitors in conjunction with 1M pots. G&L has used 200 pF capacitors, and PRS has used 180 pF in these type of circuits.
The capacitors in this set are 1000 pF and can be used to wire this type of treble bleed circuit into your guitar.
One disadvantage to this style of treble bleed circuit is that as you roll your volume down, this circuit can disproportionately allow high frequencies to pass through creating a tinny or thin sound. While this may be ideal if you are using a particularly dark sounding amp or play with long instrument cables, it can also be undesirable in certain contexts.
The second type of treble bleed circuit introduces a resistor wired in parallel into the original circuit above.
This treble bleed circuit allows for the tone to be much more even across the rolloff of the volume control. This is a very popular circuit, found in many guitars these days. A very common size for the components in this particular circuit is a 1000 pF capacitor matched with a 150k ohm resistor.
This pre wired 1000 pF capacitor with 150k resistor in parallel can be soldered onto your volume pot to create this second style of treble bleed circuit.
One disadvantage to this type of treble bleed circuit is that it is very important to use the correct capacitor and resistor values for your guitar. While a 1000 pF capacitor with a 150k resistor is often used as a one size fits all approach, it may not be right for every guitar through every amp. If it isn't the best fit, the taper of the volume pot can be negatively affected and may not be as smooth as it could be.
The third type of treble bleed circuit involves wiring a resistor into the original capacitor only circuit but this time in series rather than in parallel.
This third type of treble bleed circuit is often considered to be the best, and was popularized by a luthier in the 90's named Chris Kinman. Kinman used values of 1200 pF for the capacitor, and 130k for the resistor. Fender uses a similar circuit in their modern "Tone Saver" treble bleed circuit included on the American Professional series of guitars.
This circuit solves the issue of tinny tones at low volumes in the capacitor only treble bleed, and it also solves the issue of un natural volume taper from the resistor in parallel circuit. The only real disadvantage for this circuit is that the ratings of the capacitor and resistor used must be correct. While the sizes used by Kinman are sometimes considered a one size fits all sort of approach, it may not always be the ideal choice for every guitar.
Sets of capacitors and resistors like this one can be great for wiring up your own treble bleed circuit, and it is important to experiment to find what you want. Try soldering two long wires to the input and output lugs of your volume pot respectively, and then attach alligator clips to the end. This way, you can easily switch between not only different treble bleed circuits, but also different capacitor and resistor values. Start by trying out some of the conventional ratings mentioned here, and then experiment until you find the size that's right for what you need.
Thank you as always for checking out what I have to say about treble bleed circuits. It means a great deal to me that I'm a little tiny part of your journey with the guitar, and it's something I will never take for granted.
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