Merits and Legality of yet another DIY 312

[rp3703]

Hi,

I am posting this to gauge the merits of such a project as well as the legality of it. I am working on converting a Shure AMS8000 into an 8 channel API 312. I’m sure it sounds ridiculous but I’ve done the math and this can save about a grand versus any similar commercially sold DIY unit and require roughly the same amount of work. Now I don’t plan on going into the preamp business but I would like a little help with the PCB design(mainly verification) as well as some other interested builders who might split the cost of PCB manufacture with me. My legality concerns do not involve Shure. They have long since quit making this unit and when I asked for it, hardly even had any documentation on it. Rather, my legality concerns pertain to the 312 schematic used in this design. Minus the mute, it is pretty much a copy of Jeff’s VP312. Although Jeff did not invent the API 312 his design does add a few parts that improve on the design(Pad, Phantom, extra resistors and caps here and there). Again, while I have no plans of selling these commercially, to do what I’m talking about(purchasing PCB’s as a group), money would exchange hands. 

 

[ruffrecords]

The API 312 is basically a non-inverting op amp fitted with input and output transformers and variable gain. I think that topology is well known and in no way protectable or infringable.  The 2520 is different matter. It was clearly designed to embody specific properties that API felt were important to this specific application. They may have patented it. If they did then the patent may well have run out in which case you are free to use the design.  If they did not patent it then as soon as one was sold it became public domain and anyone could build their own version of it.

IANAL

Cheers

Ian

 

[rp3703]

The design for this project, like pretty much all other DIY 312's,  will only provide a socket for the DOA. It will be require the purchase of a separate commercially available DIY 2520(GAR2520) that is sold on CAPI website. It's probably possible to incorporate the DOA into the PCB but for the $25 Jeff sells the GAR2520 for, it would probably not reduce costs enough to justify it. There is a schematic floating around on the nets for the 2520 which other than possibly component values, is spot on for the GAR2520.