I have decided to take the advice of Mikebits and split up my
Shoe box radio thread into several smaller threads. This particular thread is for the power supply of the radio.
I have most of the power supply finished (the pictures of what it looks like can be found
here). There are just a few pesky issues that I'm currently resolving (heating issues, LED indicators, ect).
For the circuit that cools the power supply I am using 2 op-amps to control the fan. Then I added a 3rd op-amp to drive a relay to power the fan if the temp starts to become dangerous. I figured that I'd just use a quad op-amp instead of 2 or 3 separate ones. But what to do with the last op-amp?...
I decided to make a filter for the positive supply of the radio and FM transmitter to eliminate any possible ripple that may get through. There are a few questions that I have concerning this subject so that I don't need to ask in the future.
First; I have 2 different quad op-amps that I could use, the LM324 or the LM2902. Both seem to have identical slew rates, so my question is: Is the slew rate important in the design of the filter? If so how should the slew rate relate to the frequency of the input?
Second; Should I have the output of the op-amp drive a transistor or MOSFET to allow a higher supply current to the radio/FM TX? (can I even do it at all?)
Finally; Can a filter be used even if there is no noise on the line? I only ask because I did a pretty good job of filtering the noise from the line. From what I've seen the filters are just oscillators.