GML 2032 User Manual

G e o r g e M a s s e n b u r g L a b s

GML 2032 Microphone Preamplifier /
Parametric Equalizer

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.

Owner's Manual

Version 1.0

August, 2004

All materials herein © George Massenburg Labs, LLC.

GML, LLC.

Franklin, TN USA

615.790.9946 (ph)
www.massenburg.com

Combining the features of the GML flagship 8200 Parametric Equalizer and 8300
Transformerless 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 GML Model 2032 Microphone Preamplifier / Parametric Equalizer derives its power
and flexibility in large part from its features:

•• 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*

•• Transformerless; 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 MI (front panel musical instrument)

•• Wide gain range (10 dB to 75 dB) available on both inputs

•• Precision Gain switch: 65dB range in 5dB steps

•• Continuously variable preamplifier Fine gain control, +/-5dB

•• Four-band fully parametric equalizer

•• Low-frequency and High-frequency Shelf mode capability

INTRODUCTION

FEATURES

•• Flexible routing: Single-Channel, Independent, Inline Insert configurations

•• High-pass Filter; selectable 40 Hz, flat, 100Hz

•• 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

*Direct-coupled input option only. Standard production units ship with a phantom-blocking two-pole HPF in the
Preamplifier input, which include high-quality capacitors of both aluminum and tantalum dielectric materials. All
Specifications were developed and confirmed using production units. Contact GML for further information.

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.

I. Preamplifier

The preamplifier section of the Model 2032 Microphone Preamplifier / Parametric
Equalizer is based on the gain stage of the Model 8300 Transformerless 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"
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, 1kΩ 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 MI input extends the sphere of
application to the realm of the oft-neglected musical instrument. This high impedance
unbalanced input (1MΩ 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 (see Specifications page of

this manual for separation figures). 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 or MI 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.

OPERATION

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" MI 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 MI 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 MI input, the Phase function will change the absolute polarity of a
given input signal.

II. Filter

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 second­order 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.

III. 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 proven 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.

IV. Insert

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 Inline Insert operation (see Configuration illustration). 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, Inline 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 DC­servo 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 de-selected. 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” connector in the MI jack with MIC selected will not adversely affect either
the Model 2032 or the external musical instrument. The MI 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.