Good day, all!
This is my first post, and I'm very excited to be here!
I've recently gotten over the "hump" in my electrical engineering degree where things start to make sense, and all the little bits on the schematics mostly make sense, but I'm still having trouble with how reactive devices interact with circuits. I am working on a project that popped into my head the other day, and won't leave me alone.
The basic idea is a string sustainer for steel-stringed instruments, that works similar to the way an Ebow works. An Ebow basically picks up the motion of the string using a pickup coil, and then amplifies that signal, feeding it back into the string. There are a number of circuits, but they all center around LM386 audio amplifiers and tiny coils. The most successful DIY versions use little speaker coils from buzzers. I attached a graphic of the schematic I found. It's in this video (careful, loud audio in the vid):
http://youtu.be/1iccGqmEC-MThe biggest parts that I don't understand are a few of the capacitors, and how the coil impedances affect things. Does a higher-impedance (and I'm assuming, generally, more turns of wire?) coil increase the sensitivity on the pickup end? Does it increase the strength of the electromagnetic field when it excites a string (I assume so, because the magnetic field is proportional to the current and number of turns on the coil)? Do coils with more turns act as antennas, and risk more interference? Finally, on an amplifier chip, how do I know how much impedance will damage the chip, or not have a usable output? I don't want to buy a bunch of chips and toast them one after another because I have no clue what I'm doing. How would you select a coil in this situation?
Also, I'm not sure about two of the capacitors. From the datasheet for the LM386,
http://www.ti.com/lit/ds/symlink/lm386.pdf, I think that the one between pin 1 and 8 is just setting the gain to maximum. Pin 7 is called "bypass", but I don't know what it does, or why it would need a capacitor, unless it's there to filter out high frequencies by shunting them to ground? Finally, the 1nF capacitor in parallel with the input coil; I'm guessing it is a noise filter for high-frequencies and low amplitudes?
I haven't worked with ICs much yet, and I'd like to understand the process that you all go through when using a new chip, to understand and learn how to use it without frying half a dozen in the process. Or--perhaps that is the process
? I read somewhere that the LM386 is obsolete. Should I look for a newer chip to use, and adapt the circuit for that? I'm just trying to get some idea about the thought process.
Thank you all for your time.