By and large, EQ and Tone-Shaping systems come in two basic flavors — Passive and Active. Passive EQs are built upon individual components – mostly inductors, capacitors and resistors – that alter the tone directly by attenuating certain frequencies in relation to others. Active EQs are created using transistors, op-amps and other integrated circuits that need to draw power from an additional source (batteries, AC Adaptor, etc.) to create the gain provided by an active EQ. Even in most passive EQs, there are buffer amplifiers, transformers and/or tube circuits requiring power to sustain the make-up circuits that compensate for any lost gain. The Active EQ can produce copious amounts of gain for specific frequencies using discreet electronic circuitry. However, the essence of the Hartke Tone Stack is the interaction of the passive components that allow the entire EQ to behave as a single circuit, with unsurpassed interactivity between the stages.