LEVEL: After dialing in the Freq[uency], use this control to boost or cut the selected frequency by 12dB. This control is equipped with a center-detent potentiometer; just click it to noon and the frequency is flat; this means that nothing is boosted or cut regardless of Freq position.
POST: This is the volume control for the unit. The output volume is dramatically increased right before it to give you plenty of clean gain when the Pre knob is minimized.
FREQ: This control is part of the original VariOboost circuit, and Freq and Level work in tandem. Freq selects a frequency between 70Hz and 1.4KHz, which is then cut or boosted by the Level control.
PRE: This knob introduces more gain into the signal path and is configured with some high-threshold soft clipping parts. When the knob is all the way down, the path is unaffected and adds some tasteful enhancement all the way through some gentle but established soft clipping. This has the added effect of pushing the post-EQ op-amp into even more breakup.
The VariOboost accepts a center-negative DC power supply from 9 to 18 volts