Post by thread:[EE]:Adding a DC Bias to An AC Signal

Put together the circuit you attached, my original circuit just had the output (primary) of a 120/12v 300ma transformer with a 4.7uf non polarized cap across the output going to the phone; this gave me 37.8 volts ac and rang the phone. Your circuit gives me 20 AC with only 3.2 D.C at the phone connections using your instructions. I built the circuit according to your schematics; I can only assume I have done something wrong, perhaps the phone is connected to the wrong place? The only component I did not have from your schematic was the 2.2uf cap I used a 4.7uf 50v is this critical? At the off-hook connection if I place a meter here the voltage seems to fluctuate between 1.9v and 0dc with the phone on-hook if that helps. I tried a 4.7uf Non Polarized and a 10Uf Non Polarized in your circuit and it seems to give a higher output with the 4.7uf Non Polarized but still won't ring the phone. Regards, Steve {Original Message removed}