Mercury Recording Equipment EQ-P1 Program Equalizer - Used  From Other

The Mercury EQ-P1 is based on the vintage ‘Pultec EQP1a’ circuit, which uses a passive EQ circuit with a fully balanced (push-pull) gain make up amplifier. This new Mercury production utilizes only the highest quality passive components, while remaining true to the original, and like all Mercury products, has transformer balanced input and outputs.

Mercury IST switchMercury EQ-P1 Circuit (simplified)

Besides a much more powerful and stable power supply and running DC on the heaters, rather than AC, the only other modernization is one of Mercury EQP2’s most popular features: the Mercury I.S.T. Switch.

The Mercury I.S.T. Switch offers the choice to switch the Interstage Transformer in or out of the circuit. Giving engineers a choice with a flick of a switch between the standard Mercury warm, musical, "vintage" tone with the I.S.T. Switch not engaged (out) or a much more open and airy version of the same full, warm tone with the switch engaged (in). In the original Pultec EQP the Interstage transformer was always in the signal path. With the I.S.T. Switch engaged and the interstage transformer not in the circuit, there is slight widening of the sound and slightly more open top end. Many of today's engineers value this feature on the Mercury EQ-P1 and now the Mercury EQ-P2 Studio Program Equalizers to have choice between two great, but different sounds without changing their frequencies or setting and hearing the change instantly. Note: With the I.S.T. Switch engaged or not, the input and output transformers are always in the circuit.

The Mercury I.S.T. Switch makes it possible to change the characteristics of the tube by a simple flip of a switch. This flexible, modern feature can only be found in the Mercury EQ-P1 circuit. This provides engineers with the choice to use the 1:1 transformer in the middle of the circuit, or not.