Pultec EQP-1A

The EQP-1A combines a low-frequency shelving section, a high-frequency boost with variable bandwidth, and a separately selected high-frequency attenuator. It is designed for broad musical contours rather than the independently adjustable bell filters of a modern parametric EQ.

Its familiar low-end effect comes from applying boost and attenuation together. The two curves do not perfectly cancel: their different shapes and affected frequencies can produce weight with an adjacent tightening dip. Likewise, high boost and high attenuation can be balanced independently instead of forcing a single treble decision.

This is the newer Passive EQ Collection model, with transformer and tube-amplifier nonlinearities absent from Legacy. Even without active EQ, the I/O path remains relevant, and the EQP-1A models the hardware's approximately 1.13 dB insertion boost. Begin with a frequency choice, add only as much shaping as the mix needs, then compensate the resulting level. EQ Enable removes equalization while retaining circuit tone; the Bypass/Gain control provides full bypass and modern output trim.

Manual — sections: Pultec EQP-1A; Operational Overview; EQP-1A Insertion Boost; Pultec EQP-1A Controls.

• Low Frequency / CPS: Select 20, 30, 60, or 100 Hz for the low shelf section. CPS is the original label for Hz. Choose the region first, then evaluate the two associated amounts in the mix.
• LF Boost: Raises the selected low-frequency region. It works independently of LF Attenuation, so a boost is not automatically reduced by an equal-looking attenuation setting.
• LF Attenuation / ATTEN: Applies the low shelving cut. Try adding attenuation after a useful boost to tighten the adjacent low-end response. The curves and amounts are not identical, which is why simultaneous use does not simply cancel.
• High Frequency / KCS: Select 3, 4, 5, 8, 10, 12, or 16 kHz for high boost. KCS means kHz. Lower choices address presence; higher choices shape upper-frequency openness, depending on the source.
• HF Bandwidth: Controls the width around the high-boost frequency. Lower values make the band narrower; higher values spread the boost over more surrounding frequencies. Recheck the Boost amount after changing bandwidth because perceived intensity changes too.
• HF Boost: Sets the high-band boost independently of the high attenuator. The linked manual does not specify calibrated maximum dB amounts for these boost/attenuation knobs, so their panel positions should not be presented as verified dB readings.
• HF Attenuation Frequency / ATTEN SEL: Select 5, 10, or 20 kHz for the high shelf cut. This is a separate frequency selection from high boost.
• HF Attenuation / ATTEN: Controls that high shelving reduction. Use it to moderate the extreme top while retaining a chosen high-boost contour.
• EQ Enable: In engages the EQ; Out removes equalization but retains I/O coloration. It is not a transparent whole-plug-in bypass.
• Bypass/Gain: The modern model provides ±12 dB output trim and an OFF position for full bypass. Click 0 for unity, or OFF/red lamp to alternate bypass and the previous setting. Compensate the approximately 1.13 dB insertion boost plus any EQ-related loudness change before comparison. Modern frequency-label shortcuts cycle selections; they are not Legacy features.

Manual — sections: Pultec EQP-1A Controls; Low Frequency Controls; High Boost Controls; High Attenuation Controls; Bypass/Gain.