Wednesday, February 17, 2010
In my last blog I described my problem with audible hum. My father instructed me to lower the DC in my circuit by inserting 550 ohms prior to the first filter capacitor in the power supply. I did this and also replaced the first two 8mfd electrolytic caps with a single canister electrolytic with two 20mfd taps. Hum dropped dramatically with these two modifications. On my father-in-laws recomendation, I also changed the wiring to put the fuse on the incoming line side of the 120ac, right before the switch. All of these changes and the resulting voltages are in the schematic to the right. A view of the amp with the added can capacitor is here. Don't forget to click on the images to see enlarged versions.
A group of articles proved most useful in understanding capacitors, power supplies, and reducing noise. My father provided three articles which I will scan into PDFs and make available in the future. The other articles are linked below:
Repair and Replace Electrolytics
Replacing Capacitors in Old Radios
The next project I am starting will either be a power supply for reforming electrolytics, or another amp project. I have another old TV power transformer and ammunition can, as well as a pile of other parts left over from the 5E1 project.