Home > Studio Recording DIY Projects>PM1001 Mic Preamp
This is to document my latest project... building a mic preamp based on a vintage schematic. It will have transformer coupled mic inputs and transformer coupled line outputs. Class A, discrete design using transistors. I'm calling my project the PRE-1048 (a design inspired by the Neve 1272, 1073, etc...)
I draw the line driver stage schematic and designed the preliminary PCB using Eagle CAD software.
Next step will be testing the circuit....
For testing, I'll be using an output transformer that originally came from an MCI mixer console. On the finished product (a DIY Kit), I will probably use Jensen Transformers or Sowters. Though the user is free to use whatever transformer he wants, OEP, Lundahls, St. Ives, Carnhill, etc... the output transformer is NOT mounted on the PCB so you just need to wire it to the primary, and wire the secondary to your XLR/TRS jacks.
You'll also notice 2 big hunking TO-3 power transistors. The originals didn't use power transistors, but I want to use it to have that "vintage" Neve classic look. It wouldn't hurt either since these 2 transistors will be the output driver stage driving the transformer. The circuit operates in Class A, push-pull configuration.
The above PCB is just the Line Driver Output stage. If this thing works, then all I need to do is design the mic-input stage and hook the two together.
Here's the finished, etched PCB, again using the Press-n-Peel method. I'm waiting for my parts to arrive from Digikey.
For the output transformer, I'm planning on using an old audio transformer originally from an MCI 416 console mixer (see picture below). In the future, I will try out some transformers from Jensen Transformers and Sowters. The final kit will include transformers from either one of these companies.
I mounted the transformers on a prototyping board and soldered some terminals so I can use it for testing using alligator clips. And I have eight (8) of these babies.
