API 500 series 312 Pre amp for API Lunch box format. Recreation of the classic 312 pre amp. 70’s pre-cursor to the 512. Includes the crucila EA 2622 opamp. Gain and trim so you can push the op amp to get a bit of crunch and maximum punch from the mid range. They sound really good, very useulf way to add channels to your lunchbox for a great price.