From Black Lion Audio website:
"We're all fans of inducto-based EQ. While it doesn't offer the surgical precision of its solid-state based gyrator circuit cousin, it has a wonderful musical quality that's very natural sounding. Typically a good inductor EQ has, in the past, been rather expensive to purchase. A classic API or Pultec-based EQ will set you back a few thousand dollars for a stereo pair.
Since we enjoy a good challenge, our goal was to develop a transformer coupled two channel inductor based EQ that could perform every bit as well as a high priced mastering-grade setup, but do it at a lower price. Since there are lots of Pultec clones out there, we wanted do develop something that was unique. We based it on what's known as a state-variable filter, and built it around custom wound Cinemag inductors. We gave it overlapping frequencies within each set of frequency bands to enable flexibility and frequency correction when needed. We use grain oriented silicon steel transformers for the input and output stages to give the audio a nice vintage character, although amorphous core Lundahl transformers are available as an option for an additional charge.
And since we have access to a few mastering-grade inductor EQ's, we tweaked and refined the circuit until we were satisfied that it was every bit as good as the expensive brands. The smooth highs, natural mids, and thick, powerful bass that only a good inductor EQ can deliver. Go ahead; shoot it out against your Neve, Massenburg, API, or Tube Tech. We think you'll be very impressed."