George Massenburg Labs - GML 2032 Preamplifier / EQ Channel Strip
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The Model 2032 microphone preamplifier / parametric equalizer is a single-channel, multi-input device for high-resolution studio and remote applications. Incorporating the renowned 8300 preamplifier and reference-standard 8200 equalizer, the Model 2032 inherits over thirty years of GML engineering excellence. This transparent class-A discrete design with internal supply delivers reliability, musicality, and precision.
Combining the features of the GML flagship 8200 parametric equalizer and 8300 transformer-less microphone preamplifier, the Model 2032 embodies the legendary detail and accuracy for which GML is renowned. The power and functionality of these revolutionary processors is further coupled with the addition of a front panel musical instrument input, two position high-pass filter, front panel phantom and phase switching, and flexible routing options while maintaining the GML standard of performance and transparency. These advanced circuits, envisioned by George Massenburg, have benefited from over 30 years of research, limited manufacturing, critical listening analysis, widespread usage by demanding industry professionals, and continuous evaluation by the GML engineering department.
The Model 2032 microphone preamplifier / parametric equalizer offers exceptional flexibility and sonic accuracy when dealing with a variety of signal sources and conditions. Allowing quick adjustment of any critical parameter, the operation of the Model 2032 remains straightforward despite an extensive feature set. Indeed, a reduction in apparent complexity is achieved by taking a building-block approach to operational analysis.
The preamplifier section of the Model 2032 microphone preamplifier / parametric equalizer is based on the gain stage of the Model 8300 transformer-less microphone preamplifier, though there are some design changes and a few additions to expand its capabilities further than is realized in the highly specialized Model 8300 mic preamp.
Two input formats are accommodated on the Model 2032: an input XLR connector is provided on the back panel for microphone input, while the front panel sports a 1/4 in. unbalanced musical instrument connector. Input signal selection is determined by the source toggle switch.
The microphone input of the Model 2032 is an exact copy of the Model 8300 input circuitry, complete with 48V phantom power and subsequent 2-pole phantom filter. Unlike the Model 8300, the phantom power switch is conveniently located on the front panel and is illuminated to warn the user that phantom power is on. The mic input is precision electronically-balanced, 1 kilohm nominal input impedance, with tremendous dynamic range, remarkably low noise, fast slew rate, and wide bandwidth.
Adding to the Model 2032 input options, the front panel musical instrument input extends the sphere of application to the realm of the oft-neglected musical instrument. This high impedance unbalanced input (1 megohm nominal) offers low noise and low distortion, plus a wide dynamic range and ruler-flat extended frequency response to outclass common instrument inputs. Especially useful for recording bass or electric guitar, this input can also be used for a variety of other unbalanced sources such as electronic keyboards, samplers, etc.
As previously mentioned, the input signal for the Model 2032 is selected on the source switch, located near the left corner of the front panel. Only one source may be active through the channel at a time; however, signals may be present at the other inputs since the source select function does not ground unused inputs. Phantom powering may remain on, if necessary, when switching between input sources without damage to other input devices since the phantom supply does not reach the musical instrument input. It is, however, recommended that the phantom power be turned off when not in use to preserve power supply efficiency and eliminate possible DC pops when changing input source selection.
A particularly wide range of gain settings (10dB through 75dB of gain) is available for both preamplifier inputs of the Model 2032. This feature accommodates a broad array of input signals, from extremely "hot" microphone inputs to extremely "low" musical instrument inputs, which are often neglected by professional peripheral audio processing devices. Indeed, the minimal 20dB of gain found in most microphone preamplifiers can be excessive in certain circumstances, and decreases the possibility of optimized gain staging. By the same token, real-world musical instrument signals often require more than the typical 10 dB of gain commonly accorded them.
A combination of the rotary gain switch and fine potentiometer is used to control the gain setting of the preamplifier section, with the overall gain of the preamplifier calculated by adding the two control values. The gain switch allocates between 15dB and 70dB of gain in precise 5dB steps, using a combination of discrete resistors for the ultimate in accuracy, stability, durability, and sonic integrity. Providing + / - 5dB of continuously variable gain, the fine control adds elasticity to gain setting.
Incorporated into the preamplifier section, the phase switch activates a relay just before the balancing circuit of the preamp. No signal is present at the front panel phase switch -- it is merely a relay control and LED indicator voltage. Engaging this switch reverses the phase of the input signal, akin to swapping pins 2 and 3 on the input XLR. In the case of the musical instrument input, the phase function will change the absolute polarity of a given input signal.
Immediately following the preamplifier section of the Model 2032 is an extremely useful and transparent high-pass filter (HPF), which has three optional settings: 40Hz roll-off, flat response, or 100Hz roll-off. Designed for maximum clarity and musicality, this active second-order Butterworth high-pass filter is implemented with premium-grade SMD film capacitors, precision resistors, and a pristine GML 9202 discrete opamp. Passband response is maximally flat for both the 40Hz and 100Hz selections, while the Model 2032's ruler-flat frequency response is preserved in the "flat" setting. A second-order high-pass filter, this circuit creates a -12dB per octave roll-off below the corner frequency, an appropriately flexible and powerful function since many engineers use the low-frequency band of a fully parametric equalizer -- a Model 8200, for instance -- in shelf mode as a high-pass filter of sorts.
The insert out XLR signal is taken directly from the HPF output and is always active, regardless of the insert switch setting. As with all Model 2032 sections, this stage exhibits extremely low noise and distortion, wide bandwidth and dynamic range, and utilizes precise DC-servo coupling.
Parametric Equalizer :
The EQ section of the Model 2032 microphone preamplifier / parametric equalizer offers precision and adaptability when sculpting the response of any source. Its operational characteristics, duplicated from the Model 8200 parametric equalizer, have been honed through many years of use in the most critical recording and mixing situations and have proved both reliable and remarkably 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 2032 equalizer section, is the existence of overlapping frequency bands, which provide great precision and flexibility.
Specifically, this parametric equalizer provides complete control over a wide frequency range and Q setting, along with 15 dB of cut or boost on four individual bands, with the front panel controls for frequency and Q mounted concentrically. The addition of the Q characteristic empowers the user to maintain precise and musical control over the tonal attributes of the spectrally processed signal.
The availability of up to 15 dB of gain or attenuation is significant, affording the user unprecedented control from minute adjustments to dramatic alterations over completely flexible overlapping multiple bands. Thus, it is possible to achieve almost any particular sound that is desired, no matter if the goal is a subtle modification or an audible coloration effect.
Front panel controls for the Model 2032 equalizer section include an illuminated in / out pushbutton switch plus four color-coded bands with amplitude and dual-concentric frequency and "Q" potentiometers. 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 two 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.
A portion of the Model 2032's allure is the flexibility accorded the user in determining the signal routing of the preamplifier and equalizer sections. This functionality is incorporated in the front panel insert control, an illuminated pushbutton switch that activates a precious-metal contact signal relay.
Specifically, the insert function allows the user to configure the Model 2032 for single channel, independent, or in-line insert operation. Single channel operation feeds the preamplifier output post-HPF directly to the equalizer input. Independent operation allows the preamplifier and equalizer to be used on separate signal sources simultaneously, where the insert out XLR provides the preamplifier output and the insert in XLR sources the equalizer input signal. Essentially a special case of the independent configuration, in-line insert operation places an external device -- possibly a Model 8900 dynamic gain control -- between the preamplifier and equalizer sections of the Model 2032. The external device must have analog input and output to interface with the analog-only architecture of the Model 2032.
In all cases, the output XLR of the Model 2032 is the direct-coupled DC-servo corrected output of the equalizer stage, while the insert out XLR carries the direct-coupled DC-servo corrected output of the preamplifier stage, post-filter. There is, therefore, no dedicated output buffering stage; nor is there a master output level control.
Unused inputs and outputs need not necessarily be disconnected from the Model 2032 when deselected. Indeed, both outputs always transmit signal, given an appropriate input. Neither of the XLR inputs (input, insert in) short to ground when not in use. Leaving a 1/4 in. connector in the musical instrument jack with MIC selected will not adversely affect either the Model 2032 or the external musical instrument. The musical instrument input, however, does short the signal pin (tip) to ground when no connector is inserted, regardless of the position of the source switch.
V. Overload (OL) :
In light of the considerable amounts of gain available in both the preamplifier and equalizer sections of the Model 2032 microphone preamplifier / parametric equalizer, the OL (overload) indicator LED provides an essential metering function. This peak detection meter monitors both the preamplifier and equalizer outputs to preemptively warn of possible signal overload, regardless of the configuration selected on the insert control. It should be noted that although this warning LED is triggered at 24dBu from either aforementioned signal, actual clipping throughout the Model 2032 is not experienced until approximately 27.5dBu, thanks to the extended headroom of GML 9202 discrete opamps.
All-discrete, Class-A design; no integrated circuits to compromise the audio path
DC-servo and premium-grade film coupling; no interstage capacitors to add distortion or degrade over time; no tantalum electrolytic, ceramic, or aluminum electrolytic capacitors in the signal path*
Transformer-less; precision electronically-balanced inputs
Designed with GML 9202 (single) and GML 8501 (dual-differential) low-noise, low-distortion, wide dynamic range, wide bandwidth precision discrete opamps
DC-servo stabilized direct-coupled output
Multi-input format: MIC or musical instrument (front panel musical instrument)
Wide gain range (10 dB to 75 dB) available on both inputs
Precision gain switch: 65 dB range in 5 dB steps
Continuously variable preamplifier fine gain control, + / - 5 dB
Four-band fully-parametric equalizer
Low-frequency and high-frequency shelf mode capability
Flexible routing: single-channel, independent, in-line insert configurations
High-pass filter; selectable 40 Hz, flat, 100 Hz
Front panel phantom and phase illuminated switches
Front panel EQ in and insert illuminated switches
Overload (OL) indication LED
Power status LED
Low-noise, highly regulated internal linear power supply
Modern surface-mount construction, yielding maximum precision, manufacturability, and reliability
No internal signal interconnects; high-quality signal relay switching
Carbon-film and conductive-plastic custom precision potentiometers, manufactured to GML exacting standards
Multi-colored knobs, GML standard
Stylish and durable black-anodized aluminum front panel
Rugged chassis; black powder-coat finish over aluminum
Reverse-anodized front panel legend, much more permanent than ink or paint processes
Baked-on epoxy paint silkscreen rear panel legend
Quality PCB manufacturing, assembly, and chassis construction
Technical Description :
One channel, multi-input, gain, filter, parametric equalizer with insert capability and internal power supply
Mic (balanced, XLR), MI (Musical Instrument; unbalanced, 1/4 TS)
Gain control: +15 dB to +7 dB, 5 dB steps
Fine control: -5 dB to +5 dB, continuously variable
Phase switch, phantom power (P48) switch
Filter -- second-order Butterworth active high-pass filter; 100 Hz, flat, 40 Hz
Insert control: split parametric equalizer from preamplifier
EQ section: four bands, fully parametric, continuously variable controls
Overload (OL) indicator: peak indication, preamplifier and equalizer
Microphone: 1 kilohm balanced, >80dB CMRR, +17 dBu max input before clipping
Insert In: 20 kilohm balanced bridging, >40 dB CMRR, +21 dBu max input before clipping
MI: 1 megohm unbalanced, +8.5 dBu maximum input before clipping
Bandwidth: -0.1 dB / +0.002 dB, <10 Hz to >30 kHz, worst-case; -3 dB, >300 kHz and <<10 Hz, typical
<0.003% harmonic distortion, 20 Hz to 20 kHz, typical
<0.006% SMPTE intermodulation distortion, typical
30v/usec discrete low-noise precision operational amplifiers, GML 9202
Noise: -80 dBu broadband, EQ engaged, typical; -112 dBu EIN, MI input; -120 dBu EIN, microphone input (Rs = 150 ohm, 30 kHz BW), worst-case
-80 dB crosstalk, 20 Hz to 20 kHz, worst case
+27.0 dBu clipping
< 3 mV output offset, stabilized by DC servo correction, direct coupled
Wired pin 2 "hot" , 3-wire unbalanced
Internal linear power supply, 110V / 220V switch, 50 / 60Hz; + / -28 VDC, + / -18 VDC, +48 VDC
Approximate power consumption: 28W; 500mA / 250V slo-blo fuse installed (110V operation)
Separate ground and chassis connections at rear
19 in. W x 1.75 in. H x 10 in. D rack mount chassis, black anodized aluminum, silver legend
Weight: 11 lbs.