Ruby build report

[piano boy]

Finished the Ruby on perfboard. I like it! Playing an acoustic into it, built it to compare to a lil gem. I finger pick, and the Ruby is more tonally responsive than the Lil Gem to different picking positions up and down the body and on up the neck.

I had some problems during the build. Used a lm386-1 and MPF102 from Radio Shack. 1st time I fired it up had a distorted guitar sound, and then no guitar sound, just an oscillation that changed pitch with settings of the pots. Had the MPF102 in backwards! After flipping it, had distorted guitar, and volume pot changes didn't affect sound. Problem was a wire whisker across lugs 1 and 2 of volume pot.

After clearing that pots worked, but even with gain backed all the way down had some distortion on all volume settings. I put on the Zorbel network, which helped a little. I pulled the MPF102 from its socket and used a wire to connect Ground and Source sending the input signal straight into the volume pot, and had a lil gem like sound. I then pulled the wire and stuck in another MPF102 from an old minibooster build, and I had a clean sound! Turning up the gain let me distort at will. For fun I disconnected the Zorbel network and lost a little definition and got just a hint of distortion. I immediately put it back!

Now I'm wondering about the 1st MPF102 I used and why I had distortion with it. Did I damage it when I put it in backwards? Or is it slightly out of spec, and can I change other parts in the circuit to match its characteristics better (say the 1.5m resistor on the gate, or the 3.9k resistor on the source)? I don't really know what these two resistors do, but I want to learn!

Thanks for the nice project. It was very satisfying to work through the problems to a good build.