The Henriksen JazzAmp was created in 2006 to satisfy a void in the marketplace for a jazz archtop guitar amplifier that produced a pure and true reproduction of the jazz guitar tone. After having purchased a number of amps, and trying out an even larger number purporting to be jazz guitar friendly amplifiers, we saw a common flaw in the basic design of all of these amps, at least for playing jazz.
To our way of looking at it, that common flaw was in the institution of tone circuitry. Why not, we thought, create an amp with no tone controls at all. That would leave "tone color" decisions as the exclusive province of the instrument. The presumption is made that a high quality jazz archtop inherently has built in the jazz tone desired which then only needs to be made louder. Time and market acceptance has proven this to be a valuable insight. Tone controls on conventional amps can be characterized as either low pass filters (bass), high pass filters (treble), or band pass filters (middle). Most are passive filters which give them the ability only to reduce unwanted frequencies. Some are active filters which allow some level of amplification of a particular spectrum. In general, a bass control works by reducing the magnitude of higher frequencies above a certain "cutoff". A treble control works by reducing the magnitude of lower frequencies below a certain "cutoff". The problem with all of this is that all of the controls are "eating" part of your signal. In the jazz guitar world we experience this by finding that we have to choose between higher notes that are "thin" or lower notes that are "boomy". Our ear tells us that neither compromise is acceptable. So we spend the gig fine tuning the bass/treble controls in search of the "sweet spot", only to go home unsatisfied. Removing the tone circuitry completely eliminates undue influence by the amplifier and leaves the establishment of tone up to the player and their instrument where it properly belongs. Recording studios abandoned conventional tone controls in favor of graphic EQ decades ago. We saw the need to add a studio quality graphic equalizer to the amp. The purpose of the EQ is not so much to color the tone but to compensate for the environment the jazz guitar or bass is played in. Different venues carry sound in different ways. The EQ circuits on the JazzAmp are set up to increase or decrease 5 different frequency bands by +-10db. What makes a true EQ such as ours different is that is does not have any affect on frequencies outside its band. When you turn up the 300 Hz control on a JazzAmp you are affecting only frequencies between 150 Hz and 600 Hz. Turning it up actually amplifies the presence of that band in the signal path. Turning it down draws that frequency band closer to ground without having any effect on any of the other frequency bands. There is an entire paper on this web site dedicated to the use of our EQ controls. Rock amps are generally "toned" on purpose to get rid of mid range tones between 100 and 900hz and emphasize the second and third harmonic elements from 1000hz and above (lots of treble). This should help to explain why an amp that is great for rock is generally a poor choice for playing jazz. Amp makers, particularly boutique tube amp makers have bought into the idea of "toning" the electronics to achieve the jazz guitar tone. Changing the cutoff frequencies of the treble and bass controls does not alter the fundamental problem, which is interfering with the signal path via the use of tone controls in the first place. It merely serves as a fine tuner of sorts for the ear of the person doing the design. In different environments, or with a different guitar, the tone does not replicate itself in the same fashion as in the designer's studio leaving the musician to adjust the tone control and thus fall victim to the proverbial search for the coveted "sweet spot".
