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To avoid massive build errors, make sure the BOM Revision you follow matches the Revision of the PCB you are building!! The VP312DI-VPR No Input/Output (Stepped) is a kit comprised of every single part and component needed (sans opamp, input transformer, output transformer and HiZ Plug-In) to complete a VP312DI-VPR microphone preamplifier. The VP312DI-VPR is a single stage mic preamp for the 500 series format and is fully VPR compatible. The preamp is essentially an exact recreation of the legendary API 312 preamp circuit that has become the benchmark for the API sound. The DI version of the VP312 has very flexible and complete Direct Inject options built in. The aluminum faceplate is wet painted and the aluminum L-bracket is yellow chromated. How to add one or many HiZ Plug-In kits to your VP312DI Kit: There are many HiZ Plug-In options that can be used with a VP312DI preamp...passive as well as active. Too many choices to have dedicated kit bundles for each one of them. Instead, it is easier to view them as ala-carte kits that can be purchased separately, along with the DI preamp. You can select one, two or all of them if you so desire. The HiZ Plug-In subcategory can be viewed here. The idea behind this kit is for someone who has a vintage 312 card and wants to convert it to 500 series use. Besides the AP2622, AP2503 and 2520, there is really nothing worth salvaging. It should be noted that the original AP2622 is in an abnormally tall can. In fact it is too tall to be mounted standing up on the PCB. I do not think there is room to lay it down so I'd advise to check that before proceeding. YMMV This kit includes a Grayhill switch for stepped gain control. Kits using a Bourns potentiometer are also available for fully variable gain control. Complete VP312DI-VPR kits with reproduction transformers can be found here