George Massenburg Labs GML 8200 Parametric Equalizer Series II The GML 8200 Parametric Equalizer is the reference standard parametric equalizer, from the engineer who invented the concept. Its revolutionary circuitry was first envisioned by George Massenburg and is now embodied in this fifth-generation progressive design. Owner's Manual Version 1.0 April, 2001 All materials herein © GML, LLC. GML,LLC P.O. Box 1366 Franklin, TN 37065 615.790.1016 (ph) 615.794.4802 (fax) gmlinc@ix.netcom.com INTRODUCTION The GML 8200 Parametric Equalizer is the reference standard parametric equalizer, from the engineer who invented the concept. Indeed, the revolutionary circuitry first envisioned by George Massenburg and embodied in this fifth-generation progressive design affects audio signals in a most musical fashion. The Model 8200 benefits from nearly twenty years of limited manufacturing, precise listening analysis, widespread usage by demanding industry professionals, and continuous evaluation by the GML Engineering Department. FEATURES The GML Model 8200 Parametric Equalizer has become the reference standard due in large part to its features: · · · · · · · · · · · · · · All-discrete, Class-A design; no integrated circuits to compromise the audio path No interstage or coupling capacitors to add distortion or degrade over time Transformerless; precision electronically balanced input buffer and DCservo stabilized direct-coupled output Carbon-film precision potentiometers, manufactured to GML exacting standards Designed with GML 9202 low-noise, low-distortion, wide dynamic range, wide bandwidth precision discrete opamp No tantalum, ceramic, or electrolytic capacitors in the signal path Precious-metal interconnects High-quality XLR interconnects, Au over Ag Illuminated push-button switches for "EQ In" and "EQ Out" LED power indicator Multi-colored knobs, GML standard Rugged and stylish black-anodized aluminum chassis Reverse-anodized lettering, much more permanent than ink or paint processes Quality PCB manufacturing, assembly, and chassis construction OPERATION The GML Model 8200 Series II Parametric Equalizer offers astonishing precision and sonic accuracy when sculpting the response of any source. Its operational characteristics have been honed through many years of use in the most critical recording and mixing situations and have proven both reliable and amazingly accommodating. The basis of the parametric design topology, in general, specifies control over not only gain or attenuation, but also over both frequency and "Q" factor in multiple user-defined bands. In the case of parametric equalization, "Q" is defined as the center frequency of the alteration (whether gain or attenuation) divided by the bandwidth of that alteration. It follows, then, that low values of "Q" affect a wide range of frequencies around the cut or boost, while high values of "Q" specify a narrow slope around the center frequency. Another important aspect of true parametric equalization, as embodied in the Model 8200, is the existence of overlapping frequency bands, which provide great precision and flexibility. Specifically, the 8200 provides complete control over a wide frequency range and "Q" setting, along with 15 dB of cut or boost on five individual bands, with the front panel controls for frequency and "Q" mounted concentrically. The addition of the "Q" characteristic represents the foremost advance in equalizer technology since the invention of the transistor as a replacement for bulky and noisy vacuum tubes, and empowers the user to maintain precise and musical control over the tonal attributes of the spectrally processed signal. (Graphical representation of the Q characteristic and gain steps may be found in Appendix A of this manual.). The availability of up to 15 dB of gain or attenuation is significant in the audio world, since most contemporary equalizers offer at most 12 dB of cut or boost, and usually not over such flexible overlapping multiple bands. Thus, it is possible to achieve any particular "sound" that is desired, no matter if the goal is a subtle alteration or an audible coloration effect. Front panel controls on the Model 8200 Series II Parametric Equalizer include an illuminated in/out pushbutton switch for each channel, five color-coded bands per channel with amplitude and dual-concentric frequency and "Q" potentiometers, plus a power indication LED. The amplitude pots are continuously variable between +15 dB and -15 dB, with highly accurate 0 dB settings. Each band offers a wide array of frequencies to select on the outer knob of the dual-concentric potentiometer, with a good deal of overlap between bands to accommodate almost any combination of cuts and boosts. The Low and High bands offer counter-clockwise detents for shelving curves in addition to the variable "Q" values from 0.4 to 4 found in the other three bands--all on the central knobs of the dual-concentric potentiometers. Frequency markings can be found along the inner, larger ring of numbers, while the outer, smaller numbers encircling the dual-concentric potentiometer denotes "Q" value. MODEL 8200 PARAMETRIC EQUALIZER SERIES II FRONT PANEL A. The Cut/Boost potentiometer controls the amount of gain or attenuation for each band. Maximum level of cut or boost is 15 dB, continuously variable, with a highly accurate 0 dB setting (no detent). The element of the potentiometer is precisiontrimmed carbon film, for the highest signal integrity and longest life. B. The Frequency potentiometer determines the center frequency for each band. Frequency ranges differ for the bands to accommodate maximum flexibility, and are continuously variable. The inner ring of numerical markings denote center frequency in concert with the pointer; these markings are estimations and will vary slightly from unit to unit due to component tolerances. Carbon film is the element of this potentiometer. C. The Q potentiometer is mounted concentrically with the Frequency potentiometer but rotates independently. This controls the sharpness of the peak or dip for each band, with a counter-clockwise detent for shelving on the LOW and HIGH bands. The outer ring of small numerical markings denote Q value, which is continuously variable from 0.4 (widest Q) to 4.0 (sharpest Q). This is a carbon-film potentiometer. D. The Power Indication LED allows visual confirmation of the presence of appropriate power supply voltages, +/- 28 V. E. The EQ IN switch toggles between the active (switch in, lamp ON) and bypassed (switch out, lamp OFF) modes of operation. No signal is present at the switch itself; this is merely a latching DC voltage switch to control a high quality signal relay located near the back of the unit. MODEL 8200 PARAMETRIC EQUALIZER SERIES II BACK PANEL A. The Output connector provides a professional interconnect to external devices. Precious metal, durable XLR connectors are provided for each channel. Outputs are D.C. servo corrected, direct-coupled to preserve signal integrity. B. The Input connector features durable precious metal construction. This female XLR feeds the precision electronically balanced input stage. C. The 5-pin D.C. Power Supply Input allows interconnection of the external supply required for the unit to operate. A 6 ft. 5-pin power supply cable ships standard with new units. D. The Electronics Ground terminal connects to circuit ground in the unit. E. The Chassis Ground terminal gives a common point of continuity for the chassis. This terminal is normally tied to the Electronics Ground terminal (D); however, in certain situations it may be advantageous and/or necessary to keep these ground references independent (to eliminate ground loops in some installations, for instance). F. The Output Warning sticker reminds users of the inherent danger and imminent damage associated with shorting the output. Normally, this denotes that pin 2 is wired as the hot output pin; however, older units and custom-order units may be wired pin 3 hot. G. The D.C. Power Supply Pin-Out Legend reveals the appropriate voltages from the external power supply. H. The D.C. Power Supply Throughput is a 5-pin XLR connector that allows a second unit to be connected to the same external power supply without the need for a "Y" cable. I. The Ground Strap normally connects electronics ground and chassis ground; however, it may be removed by the user if it is thought to be beneficial for a particular installation. J. The GML Serial Number Tag contains a permanent imprint of the unit's assigned serial number. K. The CE (European Electromagnetic Compatibility) marking indicates full compliance with EN 55013:1990 (Electromagnetic Disturbance, Sects. 3.2, 3.5) and EN 55020:1988 (Electromagnetic Compatibility, Sects. 4.3, 5.4, 6.2, 7.0, 8.0). DESIGN Though the front panel controls seem very intuitive to the initiated and experienced audio engineer, the circuit design behind these controls is anything but simple and straightforward. The GML 8200 features exemplary input and output buffering circuits in addition to the actual equalization circuits. It is important to keep in mind that all circuits in any device necessarily alter the sonic character of any complex signal, though these colorations have been meticulously minimized in the design of the 8200. Many contemporary equalizer designs are not sensitive or wary of this aspect of audio electronics and thus require some amount of alteration to compensate for this additional spectral signature induced by the unit itself. Interestingly, care has also been taken--as in all aspects of the GML 8200--to select the highest quality components, from the potentiometers on the front panel to the smallest passive elements. This attention to detail partially elucidates the quality found in the GML 8200 Parametric Equalizer. These component choices, coupled with superior design and a proclivity towards innovation, combine to make the GML 8200 Parametric Equalizer the most powerful, flexible, and transparent equalizer ever designed. Another feature that distinguishes the GML 8200 from the myriad of other commercially available equalizers is its inherent dynamic range, which allows for the addition of 15 dB of gain in multiple frequency bands simultaneously without even a hint of distortion or loss of detail and authority. This amazing power is due in large part to the GML propensity to design all audio circuits from discrete components. Discrete designs, when executed properly, help to preserve not only sonic integrity and musicality, but also to allow for the widest dynamic range through the entire signal path, thus eliminating many sonic compromises and limitations. Not only do these discrete structures--and the GML 9202 discrete opamp in particular--sound better than their integrated counterparts, they also offer the ability to design for higher signal levels internally, while also optimizing dynamic range by providing a low noise floor. An additional benefit of the discrete circuit topology used in the GML 8200 Parametric Equalizer is increased bandwidth. Not only does this significant extension--of both high and low frequencies--provide for more detail and realism; it also ensures a greater degree of linearity in the traditional audio spectrum (20 Hz to 20 kHz) by locating bandwidth poles superceding these commonly-accepted limits. Indeed, the frequency response of the Model 8200 is well within +/- 0.1 dB from below 10 Hz to well above 80 kHz, while the +/- 3.0 dB response exceeds the ability of most audio test apparatus to measure. POWER SUPPLY Integral to the superb quality of all GML products is the external power supply. No piece of electronic equipment can operate as designed without an adequate power supply; however, most contemporary spectral processing devices do not feature a supply which can provide clean, quiet power without unduly heating the device. The GML 8355 excels in this respect, providing clean, quiet power for the many complex and sensitive circuits of the GML 8200, while remaining cool and efficient. Internal supply topologies are generally limited by board real-estate and thermal considerations and thus are almost always exclusively of one or another of the switching topologies, which results in more mains-induced noise and less ability to react to highly transient signal content or extreme circuit actions. The internal power distribution scheme employed by the GML 8200 is also responsible--in concert with the external supply itself--for preserving the highest audio quality throughout the many circuits of the Parametric Equalizer. A NOTE REGARDING NOISE It is important to keep in mind that the noise performance of the Model 8200 varies with operational settings, with an increase in noise to be expected when switching from the 'EQ Out' state to the 'EQ In' state. The reason for this characteristic is inherent to our proprietary design, which places the control b ...