Black Box Analog Design HG-2 Stereo Tube-Processor

The Black Box Analog Design HG-2 is a line-level stereo device designed to add saturation through harmonics, natural compression and increased RMS loudness when mixing and mastering.

The HG-2 uses Cinemag input transformers to feed two paths: The main signal path passes through a 6U8A pentode tube stage, which then drives into the subsequent triode stage, resulting in everything from subtle harmonics to full saturation.
In addition, the input transformer feeds a parallel signal path that uses 12AX7 tubes specifically designed for harmonics and saturation.
This parallel saturation circuit is equipped with a 3-way “tilt” switch.
The “Low” position saturates only the low mids and sub frequencies, the “Flat” position saturates the full bandwidth and the “High” position saturates only the high mids and highs.
The result is the ability to add a classy high-end to dull tracks, tighten up the bottom end or energize the entire signal.
The “Harmonics” control allows the user to control how much of the processed, parallel signal is fed into the main signal before it hits the pentode stage.
Finally, both stages achieve passive output attenuation before a pair of Cinemag output transformers.

In addition to the saturation levels, an “Air” switch adds a subtle top-end lift and the “Alt” tube knob switches between two different 12AX7 tubes in the parallel circuit.
Switching between the tubes allows the user to select the tubes for different saturation modes.

The meter selection selects whether the meter is fed from the input or output, and the “Bypass” switch is a true bypass that shorts the input directly to the output without additional circuitry.