Perhaps a vocabulary lesson is more useful than quitting the forum.
I plugged the guitar into this preamp, then into my amplifier.
The sound was just as clean as without the preamp, but boosted.
Another way to say this is that there was very little crunch or fuzz contributed by the preamp to the guitar signal.
So when I say clean, I guess I mean that there was very minimal influence on the guitar sound from the preamp, aside from boosting the signal (which is to say the amp had much more headroom with this preamp).
Again, the only Arduino experiment that I had time for was with the Realtime Audio page. I have built their circuit and had many different types of weird background noise. With this circuit, although there was still noise, it was greatly reduced. So, when I say clean, I mean that I personally got closer yesterday to Arduino guitar output that was useable for something other than 'just being able to say i did it'. I say closer because, of course, it is not perfect.
This is all inspired by the Adafruit Wave Shield and the WaveRP library.
The author of that library states that a preamp is required to place the signal between 0-5V. So, this is a rusty and low quality (I guess) way to do that.
I am only a few months in to Arduino and I have used other peoples' code and schematics so much, I was just hoping to contribute something.
Obviously and admittedly my understanding of the engineering involved is very limited.
I appreciate the feedback as I continue to learn.
I think people like you guys really enrich this hobby, and I am grateful.