To start, the bypass capacitor for the supply is 220uF and is used by all of the ICs in the circuit not just the 386. According to the PCB, the speaker is connected to ground, but for some reason my ohm meter reads that there is a 10 ohm drop some where in the circuit (without power and without the speaker attached. The missing RC network was a mistake that I made when I originally built the circuit, but once I added it, it didn't seem to make any difference in performance so I just left it out to save some parts. The 4.7 ohm resistor needs to be such a low value because if I go any higher, the transistor on the other side of the isolator will not respond to the signal. The opto-isolator is included because of a trade off that I made in the design; if I use a single 3915, then the signal will cause it exceed the reference and all of the LEDs stay on most of the time. However, if I used 2 LM3915 ICs, then the signal would only light half of the second IC which is not what I wanted.
The 741 was just a cheap IC that I decided to use for the experimenting portion of this circuit. Like I said yesterday, It is going to be replaced with an ICL7611, 1.4MHz op-amp. I don't have access to any single supply op-amps, but when I get my charge pumps in a few days, I can make a dual supply.
But now I'm still left with 3 questions;
1.) You say that I shouldn't connect the inverting input directly to the output of the op-amp, why not? In this text book that I have in front of me, they have it configured in a similar mater so I saw no harm in doing so myself.
2.) If I do use a single supply op-amp, wouldn't such a configuration cause the output to oscillate because it is constantly dipping lower and higher than the reference?
3.) You said that there is an equation for calculating the resistor value for the LEDs, what is it? I've been through the entire data sheet 3 times and haven't found it
(Also, could the LM3915 be powered by +/- 10V referenced to ground and just have the input and on the other end of the internal resistor connected to ground?) I am trying to get the LEDs in dot mode to be supplied with the necessary voltage