Description and Theory

At the heart of the Hugsley HG01 Tone Controller is a JFET amplifier which has been custom designed to emulate the non-linear transfer characteristics of a triode amplifier. Following the JFET stage is a unique tone control circuit that will either attenuate or enhance the harmonics of the amplified signal depending on the position of the tone control potentiometer (refer to Figure 1). 

                                    Figure 1. Hugsley HG01 Tone Controller

The JFET Amplifier Stage

The "non-linear" characteristic of the JFET is what generates the spectrally rich array of harmonic frequencies (commonly referred to as "Distortion Artifacts") within the JFET amplifier stage.

In a classic guitar amplifier signal chain there are basically two types of distortion artifacts. The type of distortion generated in an overdrive, or "fuzz box", design is that of "clipping" (refer to Figure 2) and is primarily responsible for odd-order harmonic generation. 

                                               Figure 2. "Clipping" Distortion

The second type of distortion is known as "even-order" harmonic generation which is generally agreed upon as having a musically pleasing tone. It is this even-order harmonic generation that is characteristic of a class "A", or "single-ended", vacuum-tube-triode amplifier much like the 12AX7 (refer to Figure 3). 

                                             Figure 3. Even Order Distortion

If an amplifier where truly linear, the only frequencies measurable at the output would be the frequencies, or "signal(s)", driving the input multiplied by some "gain factor". This "linear" characteristic is what recording engineers strive for but it is not what musical instrument designer's desire.

Tone Analogy

An appropriate analogy to illustrate the theory behind the Hugsley Tone Controller would be a musical instrument like the clarinet which operates by blowing air over, and thereby "exciting", a vibrating reed. This "reed-vibration" will generate a rich spectra of audible frequencies that are either enhanced through resonance amplification or diminished through selective filtering based on the clarinet's physical, or acoustical, dimension.

The resultant "tone" will be unique to the clarinet and clearly discernable from other reed-type instruments (e.g. the saxophone).


The Hugsley Tone Controller is perhaps the most unique, active, "In-Board" analog circuit offered for guitar tone dynamics.