2017-09-05 18:30:11 +0000 - Written by Carl Burks

I picked up a great book on musical electronics projects from the site HumbleBundle. It is published by "no starch press" whose tag line is "the finest in geek entertainment". After watching the Ben Heck show and seeing Felix build a preamp in an accoustic guitar I was pleased to find a preamp project in a book I just bought. Junkyard Jam Band is available in print and as an ebook. The author David Erik Nelson writes both fiction and maker type books. This particular book struck a chord with me and as soon I as read it I went online and ordered the parts I needed. The first project I wanted to complete I found on page 127 "The Mud-N-Sizzle Preamp". I couldn't find the 1.5 uF capacitor, or mono 1/4 jacks in stock so I replaced the 1.5 with a 1 uF capacitor which I then replaced with two 1 uF wired in parallel. I replaced the mono audio jacks with stereo which weren't much more in price, but added a bit of complexity to my project.

After waiting for my parts to arrive I took a project enclosure I had gotten when Radio Shack was going out of business. I laid out the parts on the enclosure and drew around them with a sharpie and began to drill. I had an issue because I didn't think about the audio jacks bumping in potentiometers. I offset the in and out ports to match other pedals in my pedal chain. It didn't match the book's layout, which wouldn't have required as much work, but since I had already drilled the holes and was happy with the layout, I filed down the plastic seperator one one of the audio jacks. I followed the other directions and having the schematic was quite helpful. It didn't take to long to solder and I was able to plug everything up and test it out. I had to change out how I soldered the audio jacks. I was testing with a head phone which had a 4-conductor and that tripped me up a bit.

I put the battery in and connected everything and I could hear the guitar. Plugging in directly to the guitar the signal isn't strong enough to hear at least not very well, so in comes the pre-amp. Plugging the guitar into the preamp gives a strong enough signal. Amps typically will work with an electric guitar without a preamp, but I like how my guitar sounds when I plug in the preamp then the main amplifier. After that I carefully closed up the enclosure and tested it again. I then used my Dynamo to make some temporary labels.

What next?

I'll probably swap out the 9v battery for a wall connector. If I wire a DC jack and connect it to another 9V lead, I can use it with battery power it I need to. If my 3D printer were larger I'd probably print an enclosure where the battery was seperate from the rest of the wiring. I still need to print some knobs to cover the potentiometers. I will also use my cricut to make the graphics replacing the ones I made using a dynamo label. I might add a switch to add addition signal boost/fuzz with another transistor, the book includes instructions for adding a second transistor on page 217. If I had it to do over again I would have moved the power switch to the top rather than the face of the enclosure.

Here is a shot of the current state of the project.



Further Reading

Wikipedia - Phone Connector Audio Wikipedia - Preamplifier Sparkfun's Learning for Transistors Sparkun Transistor Application Amplifiers