AS OF JULY 2024, THIS PCB IS NOT YET "VERIFIED." Although it should work just fine and various checks have been taken to ensure it's functionality, still USE AT YOUR OWN RISK.

Chiming in here with a quick and dirty utility project. This stuff is taken straight off of data sheets — I can’t take any credit here for the circuit.

I plan to build some of Ian’s “Poor Man’s Pultec” filters and wanted to replicate the solid-state EQP-1A3 gain stage. It turns out that this is essentially an implementation of 2520 data sheet/application notes, similar to the API 325 Line Amp or Melcor line amps.

This board allows for various implementations of the unbalanced-to-balanced 2520-based line amp scheme used in the solid-state Pultec EQP-1A3, API 325, etc.

The board has a cutout that will fit a Jensen 123 / 2503 / Profile 4804 / CMOQ-2(?) size output transformer, with hookup pads placed close to the edge of the board for easy connection of a different transformer if needed. The original EQP-1A3 line amp obviously does not have adjustable gain or output attenuation and while I don't plan to use them, I added those options from my aforementioned other project because again, this is meant to be a universal/utility board. You could probably mount a bunch of these boards upright in a 2U chassis and build whole rack of line amps.

There are many, many options for populating this board (which was the goal), so I thought it would make sense to share it "open source" with the GroupDIY forum.

In the attachments, you'll find a complete .pdf with schematic docs and BOM

...and as explicitly stated: this is an open-source project for D.I.Y. purposes only, not for resale and not for profit.