USBPre: the world’s very first USB mic preamp

The first-generation USBPre was the very first USB microphone interface ever, from any company. I had been playing around with this new ‘USB’ computer protocol and a SPDIF-to-USB box from Opcode. It dawned on me that I could design a couple great mic preamps and supply the necessary amount of power for true 48V phantom all from the 2.5W that USB supplied if I did the power supply carefully, which was not a problem. At this point in my career, I was very strong in analog design, but less so on the digital side of things, so Jim Allard from Allard Designs did much of the work on the digital side of things. Today, there are hundreds of microcontrollers available with a USB peripheral built in, but back then the only game in town was the UDA1335 from Philips, and it left a lot to be desired but we wrapped enough parts around it to make it work for our purposes. The housekeeping was done with a venerable PIC processor. Like all of these other early products, Libby Koomar designed the mechanicals. I was very happy with the mic preamps I did in this product – all discrete, class-A, our first transformerless design. In the first couple years we shipped the USBPre, we spent a lot of time working directly with Apple and Microsoft, as both of their OSes were full of bugs in the new-to-the-world USB Audio class. Several months after shipping, we came out with a revision, USBPre-1.5, which included the much-requested SPDIF In and Out. Since this came out, there have been dozens of great (and not so great!) USB interfaces from other companies – many still bear a passing resemblance to their original predecessor.