The Mercury EQ-H1, EQ-P1, EQ-H2 and EQ-P2 are all based on the original Pultec equalizers which were tools developed to deal with the limitations of recorded music. Limitations that most often manifest themselves in the highest and lowest frequencies of the program material. The Mercury Studio Program Equalizers, like the family of original Pultec EQs, are originally designed to bring back the life and musicality lost in a recording. Whether by accident or genius, nothing has been able to do this better in music production than a passive equalizer with tube gain make up amplifier ('Pultec style') equalizer. The interaction of the passive boosting and attenuating shelving EQs (not relying on negative feedback), as well as the transformers, tubes and other amplification circuitry all add to the incredibly musical character of the product. Working engineers try other types of equalizers, but always end up coming back to the Pultec style as the equalizer of choice for those final touches while tracking or mixing and even mastering at times.
Now in this modern age of digital recording, where the source you put into the DAW is exactly what you have on the track, with no rounded edges, no slight compression and none of the “pixie dust” that came with analog tape, the Mercury family of equalizers are needed more than ever to help add the musicality, warmth and tone to your tracks that we have all treasured.
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.
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.