Chameleon Labs 7603 Microphone Preamp & EQ

Its fundamental design architecture retraces the path of revered, classic pre-amps of the past as well as our popular 7602. Our engineers at Chameleon have worked tirelessly in developing new, pivotal components that allow us to take the next step forward in performance.

These enhancements start with all-new proprietary microphone and line-level input transformers that feature custom-made nickel laminations and bobbin assemblies—all designed in-house. By developing new engineering processes focused on the material science associated with lamination manufacturing, Chameleon was able to develop a lamination “recipe” that delivers optimized audio performance, providing the 7603 with high bandwidth and incredibly low distortion.

Design of our new transformers was based around the need to capture and preserve the delicate audio input signals’ truest form, and so they are enclosed in high permeability MuMetal enclosures, designed to protect sensitive audio signals from radio frequencies, spurious and parasitic noises.

Once your audio exits the input transformer, our circuit boards are carefully crafted to ensure the highest possible signal integrity. As a starting point, we developed a new discrete audio input gain stage based on our vision for a solid topology that provides extremely low noise, high dynamics and extreme bandwidth. All of the 7603’s operational amplifiers used throughout the device are based on this topology.

The 7603 features EQ stages with four different available adjustments—Variable High Pass, Low Frequency Shelving, Mid Frequency and High Frequency Shelving. Our engineers made a conscious decision to stay with the same, desirable, inductor-based topology that made our 7602  so popular, however we implemented our new discrete Op Amp to drive signal through a new set of custom Chameleon designed and manufactured inductors, providing the musicality we all love to use.

The output stage of the 7603 is unique with respect to its design and performance. It can be described as a variable-gain circuit that simultaneously adjusts both the input and output levels in order to generate a lower noise floor and extraordinary audio performance.

The 7603 pre-amplifier provides a desirable set of user selectable functions designed to make the unit flexible and an integral part of the artistic process, incorporating a full portfolio of traditional features as well as some not commonly seen on other pre-amps.

Microphone input impedance can be selected between 300 and 1200 ohms, providing a method by which a microphone can be more ideally matched to the input stage and making it easier to get the best from lower output microphones such as ribbon-based designs.

We added a low impedance Direct Input on the front panel for plugging in instruments such as guitars that can be run through the line input stage, and added a precision VU meter with custom ballistics for visual monitoring of either the input or output levels.

SPECS:

• On Switch:

  Turn Pre Amp On - VU Meter Light

• 300Ω / 1200Ω Switch:

  Switch between 300Ω and 1200Ω input impedance for the mic input

• 48V Power Supply Switch:

  On/Off

• DI Switch:

  Direct Input with 100KΩ input sensitivity

• EQ Switch:

  Engages audio high pass filter and equalization circuits

• Polarity Switch:

  Reverses the polarity of the audio signal

• Mic/Line Sensitivity Switch:

  +20dB to +70dB of mic boost and -30dB to +20dB of line level adjustment.

• High Pass Filter:

  Provides a 15dB/octave high pass filter at 40Hz, 80Hz, 160Hz and 320Hz

• Low Frequency Equalization:

  Provides +/-15dB of Boost or Cut at 35Hz, 60Hz, 110Hz or 220Hz

• Mid Frequency Equalization:

  Provides +/-15dB of Boost or Cut at 360Hz, 700Hz, 1.6kHz, 3.2kHz, 4.8kHz or 7.2kHz

• High Frequency Equalization:

  Provides +/-15dB of Boost or Cut at 3.4kHz, 4.9kHz, 7kHz, 12kHz or 16kHz

Inputs

• Microphone (XLR):

  Transformer balanced input, RF isolated

• Line (XLR):

  Transformer balanced input, RF isolated

• Direct In (1/4” TRS):

  High impedance instrument input

Input Impedance

• Microphone:

  300Ω or 1200Ω

• Line:

  10kΩ line bridging from 600Ω or lower source impedance

• Direct Input:

  100kΩ

Sensitivity

• Microphone:

  From -70dBm to -20dBm in 5 dB steps for 0dBm output

• Line:

  From -30 dBm to +20 dBm in 5 dB steps for 0 dBm output

• Noise Specification:

  Better than -125dBm EIN between -80 and -40 dBm referenced to 600Ω input impedance, SNR 116dB at maximum output

• Output Type:

  Transformer balanced and floating to drive 600 Ω load

• Maximum Output:

  +28dBu into 600Ω load impedance

• Frequency Response:

  10Hz - 20kHz -0.5dB 10Hz - 50kHz -1dB

Indicators

• VU Meter Light:

  Power ON

• Red Input Gain:

  Input Overload

• Red Output Gain:

  Output Overload

Power Supply

• 100V - 240V (50/60Hz):

  Switch mode power supply, fully shielded 3 amp peak output capability, quiescent consumption 0.5 Watts

Mechanical

• 1RU Steel enclosure
  Aluminum front panel
  Laser etched graphics
  Milled aluminun knobs