Pultec EQP-1A Legacy EQ

The EQP-1A Legacy is UA's first-generation Pultec emulation for UAD hardware. Its musical role is still low-end contouring and high-frequency shaping, but it should not be described as the modern model with a different badge: the manual explicitly excludes transformer and I/O distortion modeling to conserve DSP.

The filter architecture combines a selectable low shelf, variable-bandwidth high boost, and a separately selected high attenuator. Simultaneous low boost and cut remains useful because the two curves are not exact opposites. It can add weight while changing the neighboring bass contour, rather than merely returning to flat.

Use Legacy when those established EQ interactions are wanted without the newer nonlinear additions or DSP cost. Choose frequencies, balance boosts against attenuation, and compare using external level compensation if needed. The linked manual documents a shared approximately 1.13 dB EQP-1A insertion boost. Its Legacy bypass knob does not provide the modern ±12 dB output trim, and modern frequency-label cycling shortcuts are also excluded.

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

• Low Frequency / CPS: Select 20, 30, 60, or 100 Hz. CPS means cycles per second, equivalent to Hz. These are discrete selections rather than a continuously sweepable cutoff.
• LF Boost: Adds a low shelf around the selected frequency. Establish the amount by listening to the instrument in context; the manual does not supply a calibrated maximum dB range for this knob.
• LF Attenuation / ATTEN: Applies low shelf cut using the same frequency selector. It can be used with Boost because the curves differ in shape and effective frequency. Equal-looking knob settings do not guarantee cancellation; recheck the entire low-end contour as you combine them.
• High Frequency / KCS: Sets the boost frequency to 3, 4, 5, 8, 10, 12, or 16 kHz. KCS is equivalent to kHz. This selector does not set the separate high-frequency attenuator.
• HF Bandwidth: Lower values narrow the high boost; higher values affect more surrounding frequencies. Treat it as width, not a separate gain adjustment, and reconsider the Boost amount after moving it.
• HF Boost: Determines high-frequency boost. Pair a broader setting with modest amounts for general tonal change, or narrow the width when focusing on a particular presence region.
• ATTEN SEL: Independently selects the high-cut shelf at 5, 10, or 20 kHz.
• HF Attenuation: Sets the amount of that high shelving reduction. Combining high boost and attenuation can shape the top end more specifically than either control alone; there is no verified dB calibration stated here for the amount scale.
• EQ Enable: Removes the EQ action in Out while retaining the modeled I/O path. This is distinct from disabling the whole plug-in, even though Legacy does not model the modern transformer and I/O distortion behavior.
• Bypass Knob: The Legacy control is bypass only—there is no output gain adjustment. Use host gain compensation for fair comparisons, accounting for the modeled approximately 1.13 dB insertion boost. Do not infer the modern ±12 dB trim or frequency-label cycling shortcuts from the shared manual illustrations.

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