Hardware Blog: SC-1 Mic Preamp Kit

(Guest blog by Ruel Oquindo, Five Fish Studios.)

Earlier this year, I decided to design my own mic preamp. I wanted my preamp to sound better and cleaner than most commercial preamps out there but I also wanted it to be inexpensive. I believe that great sound doesn't need to cost thousands of dollars.

I created a blog documenting my adventure. Pretty soon, I had a dedicated following on the web watching/reading my struggles as I worked through problems with my design, noise issues and other things. A lot of my readers expressed interest in buying a couple of channels, and pretty soon, I was adding more features and making it user-friendlier to build and assemble for the DIY'er.

After months of working on this project during my spare time, it's ready. I am calling it the SC-1 Mic Preamp Kit. It's basically a transformerless, all solid-state design using chipsets from THAT Corp and Burr-Brown. It boasts clean gain from 6dB to 72dB, via a 12-position gain control switch. This high-gain, transparent mic preamp is especially suitable for dynamic and ribbon microphones. Phantom Powering via a slow ramp-on +48Volts is also included for working with condenser microphones. Other features under the hood are RFI protection on input and outputs, input clamping protection and output surge protection.

No special tools were required in building this preamp kit. No SMD parts or esoteric construction techniques. All parts in the kit are labeled in individual zip bags so the user doesn't even need to know resistor color-coding or capacitor coding! The only special tool I used is a magnifying glass but that's only because my eyesight is not as good as it used to be.

The preamp board itself measures around 3"x4". Everything on the board is clearly labeled with the part# and part value. In fact, you can assemble this board without looking at the printed instruction and just follow the part values written on the board.

All components used are through-hole mounted. The only critical part to solder is the selector switch. Only because there are lots of pins, and they're spaced very close together.

Here's a photo of the finished preamp kit. The controls, from left to right, are the 12-step gain selector switch, LED lamp to indicate +48V phantom power, Phantom Power Switch, and Trim/Volume level control.

All you need is a project case or rack-mounted case.

And here's a photo where I put 4 channels of this preamp in a half rack case. I also designed the Power Supply circuit to power this preamp. It features regulated +18, -18 voltages and also a regulated +48Volts for phantom power.

And there you have it I hope this little write-up has inspired you to pick up that soldering iron and do a DIY project!

For more info visit Ruel's FiveFish Studios.

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