I’ve seen plenty of preamp kits and microphone mods in Tape Op and on the internet. It’s relatively easy to find complete kits to build your own Neve or API preamp clone. There are several tube preamp kits around as well. Only recently have I come across DIY plans for the next link in the audio chain: compression and limiting.
It’s nearly impossible to find a professional studio that does not have at least one 1176LN (FET based) and/or LA-2A (tube/electroluminescent based) in the racks. These are the classic compressors/limiters, and as such they do not come cheap – about $2000 and $3000 per channel.
These designs have been around for 40 years or more. I’m not sure why (copyright or patent issues?) but no one seems to offer a complete kit.
Hairball Audio comes close with on the 1176 though…They offer a kit (aprox $350) with a pre-drilled chassis and all the hard-to-find components: audio and power transformers, VU meter, FETs along with all the custom knobs, buttons and switches. All of this is designed to work with custom made PC boards by MNATS in Austrailia ($26), which are based on a design by Gyraf Audio in Denmark. They’ve got a pre-set shopping cart at Mouser Electronics to round out all the rest of the parts (aprox $80). So for about $475, and the time it takes to build it, you’ve got an 1176LN.
The LA-2A is a different story. Schematic here. It’s tube based, so there are higher voltages to deal with. And it uses a custom-made “T-4” electroluminescent cell, which is easily the most expensive and hardest to find component. I’ve yet to find a complete source for a DIY version, but there are a few sites that come close. The most exciting is (to me) is the Drip Opto 4. This $150 PC board seems to be the easiest way to get into a DIY LA-2A. Drip Electronics also custom makes their own t-4 cells, along PC boards with a bunch of other boutique projects. Check out the the amazingly well designed documentation for the Opto 4 (pdf):
Of course, the real-deal vintage LA-2s were built with point-to-point wiring – no printed circuit boards. I’m not sure I could have the patience to do that (hell, I’m still not sure I have the patience to put one of these together on a PCB), but DibS LA-2 project is pretty amazing:
Great blog post on DibS DIY LA2 All point to point, excellent DIY enclosure!