The Pultec EQP-500X is a 500 series adaptation of the classic EQP-1A Passive EQ, mixing the best attributes of the EQP-1A3-SS and EQP-1S3-SS.

The Pultec EQP-500X uses an op-amp based on the API 2520 replacing the valves found the original EQP-1A. The API inspired op-amp provides a cleaner and more transparent tone without sacrificing the depth and musicality Pultec EQs are known for.

A mixture of the EQP-1A3-SS and EQP-1S3-SS, the EQP-500X features a unique blend of frequencies with an increased amount of high peak boost frequencies (1kHz, 2kHz, 3kHz, 4kHz, 5kHz, 8kHz, 10kHz, 12kHz and 16kHz). It further includes two shelving boost frequencies of 5kHZ and 10kHz. High attenuation frequencies include the classic 5kHz, 10kHz and 20kHz.

The Low band offers the same frequency choice as on the EQP-1S3-SS (30Hz, 40Hz, 70Hz, 100Hz)