User Manual

SM Pro Audio Page 6 of 12 Tubebox manual
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4 Audio Connections
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The Tube Box features a 1/4” (6.5mm) TRS connector on the front panel for connection of a
Balanced Microphone or unbalanced instrument. All other connections are done thru the back panel
multipin connector. Note: The Tube Box accepts mic or line level input signals. Do not connect your
power amplifier outputs to the Tube Box inputs!
5 Preamp control
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Input controls for the preamp are:
Rotary INPUT GAIN (labelled 0 to 10),
PAD(-20dB)
48V Phantom power switch.
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A Peak LED is also provided to indicate when the input level exceeds the preamps operational level
and sends the unit into square wave (distortion), which sometimes may be a desirable effect.
6 Optical Compressor
Why Optical Compression?
Optical compressors have a smooth gradual release curve making them very musical. This style of
release is not usually found on a solid state or tube compressor. It acts as an attenuator on your
volume path, splitting the signal between a resistor and an LED light.
COMP - Compression on/off switch
Simply turns the compressor stage on or off. When you switch on the
compressor, the VU meter will change to show Gain Reduction rather
than output volume.
Rotary compression control
The rotary compression control (labelled 0 to 10), sets the amount of
compression. It expresses the difference between the input level
change and the output level change. The higher the amount of
compression, the smaller the dynamic range.
Att - Rotary attack encoder
The rotary attack control allows for adjustment in milliseconds. Attack is the time it takes the
compressor module to respond to the corresponding input signal before gain reduction occurs. Short
attack times quickly bring down the level of the loud, fast transients in the audio signal; long attack
times let more sound through before the compressor engages, resulting in a punchier sound.
Rel - Rotary release encoder
The release control sets the time in seconds it takes for the compressor module gain to return to the
point of no gain reduction in the absence of audio program material. Short release times create a
more exaggerated effect (“breathing”), whereas long release times have a more gradual decay.