Thanks for the great project/tutorial. I have enjoyed reading it. Much more logically laid out than the first project. I prefer this approach instead of following lengthy threads.
You are most welcome. Different approaches work for different people. When I read the first project, it seems very interactive. Everyone was working together and enjoying the fun as the project evolved. Actually, I was hoping to start the same kind of free for all. ;-) So it's not working out the way that I planned, but it seems to be working out all the same.
Some things that aren't perhaps immediately obvious to the newbie reader of this project are... perhaps:
- The reason for R7? What effect does a lower or higher current have on the circuit?
- The purpose of capacitors in the power section is mentioned, but how exactly these work is not clear... as in why are these connected to ground, rather than in series with the circuit? How exactly do they filter AC? Where does AC come from when using a 9vDC supply?
- How does the feedback loop work exactly? And what do the capactors and resistors do? How is the feedback loop used to set the gain?
- The flow of current through the circuit. The audio signal might seem obvious, but newbies learning about electrical currents might not get this even though it's project #2. Quite often concepts are skipped over earlier on, and people can come unstuck when things get a little complicated later on. I am guilty of learning to build/mod things and not quite understand why something works.
Perhaps these clarifications might prove useful to newbie readers? Just a suggestion, not a criticism.
No worries! I appreciate the feedback. It makes another opportunity for someone to learn something. I never know when I am going to come across new information that I am ready to absorb. So, when I think I know an answer, I like to offer it when the opportunity comes along. Because you made the suggestions and many newbies will have these questions, here are some answers. And here's the schem from "1. Introduction" for easy reference:
R7 is the resistor in series between the 9V power supply and the circuit. It is followed by C6, a 100uF capacitor that has its other lead connected to ground. This pattern of components appears in lots of places and it is helpful to be able to recognize it. For example, R6 and C5 (right after the op amp) are in the same configuration. Both combinations are low pass filters. That is, they filter out high frequency AC. The low pass filters in this circuit have different component values and "roll off" the frequencies differently. The R7/C6 combination filters out a lot more than the R6/C5. It is set up this way because the R7/C6 low pass filter is there to clean up the power supply. The R6/C5 combination filters the audio signal and is part of the character of the sound that the circuit produces.
A lot has been written on the forum explaining these filters, so I won't repeat it all here. If you happen to like my writing style, then you might find what I have written on my own site helpful:
gaussmarkov.net: low pass filters.
The short answer on how the capacitors work in these low pass filters is that they act like fast rechargeable batteries. Whenever the voltage changes in the power supply or audio signal, the capacitor gives or takes electrons that smooth out the changes. So in the power supply application, you might think of the capacitor as an additional power supply. Your 9V battery has one end connected to the circuit and the other connected to ground and that's the way the capacitor is hooked up also. I have also written more about this on my site:
gaussmarkov.net: ac and dc. This stuff helps to explain the low pass filter stuff that I just mentioned above.
as far as the feeback loop, let's start with the reply i gave here:
I am digging it and see if there are more questions.
i hope this helps.
