Taking the solid-state EQP-1A3-SS and EQP-1S3-SS and condensing them into a convenient 500-series form factor, the Pultec EQP-500x is a 2-band program EQ sporting a solid-state API 2520 op-amp for the gain stages. The EQP-500x otherwise features the same parts and specs as the EQP-1A3 and offers 30 to 100 Hz shelf boosting or attenuation, 1 to 16 kHz peak boosting, and 5 to 20 kHz shelf attenuation.
Further controls include a 5 to 10 kHz shelf boost and an EQ In switch. The amplifier delivers a flat 20 Hz to 20 kHz frequency response. This module consumes one 500-series rack unit. Each EQP-500x is made in the USA.
This version of the EQP-1A3 is actually preferred by some engineers for certain applications (kick, snare, bass, piano, etc.) and also serves as the core for the Pultec 500-series EQs. Many users of this version of the Pultec describe them as more punchy and having a tighter low end than the tube version.