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Tone Control and the Graphic Equalizer

By Grace Griffin,2014-08-09 18:16
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Tone Control and the Graphic Equalizer

    Tone Control and the Graphic Equalizer

    Using the Henriksen JazzAmp?

    Using the JazzAmp? is pretty much straight forward except that an explanation of the use of the equalizer channels is in order. Other than that, there is a single input for your instrument and a line out which will deliver the signal from the preamp to an external board if you wish. While we hope you will read this entire document If you become impatient, skip to the last page and read the “Experiment to Learn” section.

Extension Speaker

    On the back of the amp is an extension speaker jack. Do not plug in a load with an impedance less than 8 ohms or you may cause the amp to overheat. Adding an extension cabinet increases the basic power of the amp from 60 watts rms to 80 watts rms on the 10” and from 115 watts to 160 watts on the 12” .

Standard Tone Controls

    One of the great, but unconventional, features of the JazzAmp is the fact that it has no standard tone controls. To understand why we call this “great” a brief understanding of what a standard tone control does is necessary. We will try and achieve this with as little “technospeak” as possible.

    Electronically, a tone control functions as a “passive band pass filter” with a variable control. What this means in actual practice is that each of the tone controls, treble, bass, mid is “filtering” the signal coming from your instrument. There is no way to get an exact reproduction of the signal from your instrument as each of the tone controls is adding at least a minimum of its own influence on the signal. The most common objection heard about amplifiers from jazz guitarists is often phrased in terms of the amp either being to “thin” or tinny on the top strings, or too “boomy” on the lower strings. Most guitarists spend a good part of each gig tweaking the treble, bass, and mid controls in search of the “sweet spot”. The technical truth is, the nature of the tone control design prevents the actual reproduction of the signal provided by the instrument.

    Each instrument, (be it archtop guitar, acoustic bass, mandolin, violin, etc) has sound properties acoustically which were painstakingly created by the luthier. The goal of the pickup selection has never been to make an archtop guitar sound like a solid body guitar. On instruments with pickups, the pickups are also part of a “work of art” intended to aid the amplification of the acoustic properties of the instrument. Most pickups include a

    single standard tone control with a range from bass to treble, which when properly matched to the instrument give the player an element of control over the flavor of the signal sent to the amp, but do not “eat” the acoustic properties of the instrument.

The Graphic Equalizer

    The JazzAmp was created to faithfully reproduce the work of the Luthier, including the choice of pickup, without introducing any “personality” of its own. Use of standard tone controls would make this impossible so we didn’t do it.

    However, there are circumstances in which the musician needs greater control over the reproduction of the instrument to accommodate other realities.

    High quality recording equipment long ago abandoned the use of conventional tone controls on the board and added multi-band graphic equalizers in their place. These controls are used in moderation to adjust such things as the tonal properties of the room in which the artist is performing. In much the same way, we are all aware that no venue transmits the sound from the bandstand to the audience in an acoustically perfect form.

    The EQ (short term for graphic equalizer) was added to the JazzAmp to allow the musician the opportunity to more closely reproduce the same tone on the gig that is achieved in the recording studio.

Understanding the Controls

    On the EQ, the control does not change the frequency of the tone being passed as it does with a conventional tone control. The controls are best thought of as a volume control for only the frequency that is marked.

    The controls are labeled in Hz and kHz. The term Hz or Hertz, replaced the phrase “cycles per second”. k represents the number 1000. So 1kHz is equal to 1000 cycles per second. In musical terms, we are familiar with term A-440. the 440 is equal to cycles per second, or in modern electronic language 440 Hz. The term “frequency” is the number of times per second that the note oscillates, or vibrates.

    On a guitar, A-440 (Hz) is located on the fifth fret on the first string. An octave higher is thA-880 (Hz), at the 17 fret on the first string. In the other direction an open A string is A-110 (Hz).

    To correlate this to the EQ on the JazzAmp There are two more things that are necessary to understand.

    1. A-440 is the “fundamental” or center frequency of the note. A vibrating string has

    many harmonics, or overtones and undertones, in addition to the fundamental

    frequency.

    2. The frequencies as marked on the JazzAmp are the center frequency that is

    affected by the control. A frequency range from half the center to twice the center

    is affected by the control. Thus, the 100 Hz control will effect the volume of

    frequencies between 50Hz and 200Hz. The 300Hz control will have an effect on

    frequencies from 150Hz to 600 Hz, ect.

Experiment to Learn

    Begin with all the EQ controls set on the 0 mark, or half way. Turning any control clockwise increases the volume of the selected frequency by up to 10db while turning the knob counterclockwise will decrease the selected frequency by up to -10db.

    You will note that the 10 kHz appears to have little affect, while the 100 Hz has a great deal of effect on the sound. The 3 kHz will appear to have minimal effect, but more than ththe 10 kHz. This is because the highest A note on the guitar at the 17 fret only has a

    fundamental frequency of 880 Hz. The higher controls (10 kHz and 3 kHz) are either increasing or decreasing only the harmonic overtones produced by your guitar.

    The 100 Hz, the 300 Hz and the 1 kHz have a direct effect on the fundamental notes on your guitar. Let us suppose that you have a guitar whose pickup has a disproportionately loud output on the lower E string. In the past you have dealt with this by rolling off the standard bass control. But in so doing the price you pay is that the top E string gets thin sounding. On the JazzAmp you can “turn down” the volume of the 100 Hz control to balance the output of the pickup without affecting the sound of the top E string at all. Practically speaking this is the actual meaning of the term “Equalize”.

    As you play with the controls you can see that the three controls of lower frequency 100 Hz, 300 Hz and 1 kHz all have different effects on different strings.

    If you have a guitar for which the signal output is both acoustically and electrically (the pickup) balanced from the highest notes to the lowest notes, then the proper position for all of the controls should remain set on 0.

    The best way to use the EQ is to spend some time in a controlled space and play while listening to the sound. If you find that any area of the neck seems too strong or too weak work with the corresponding EQ channel until you are happy with the balance.

    You will notice that the tone control on your guitar has a greater effect on the “brightness” or “darkness” than you might be accustomed to. The natural “warmth” of your guitar will shine through both in “bright” or treble, and “dark” or bass settings of your guitar’s tone control. Let your ear be your guide.

    In a gig situation, after you are familiar with how your EQ needs to generally be adjusted in your home space, you may find that the room carries sound disproportionately such as too much bass or treble. You will be able to use the EQ to compensate for poor rooms without messing up your basic tone by adjusting slightly the EQ for the offending frequency of the room.

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