Can anyone explain why circuit A has a totally silent output while circuit B has a low amount of hiss on it's output? All resistors are metal film (1%) and so are the capacitors (5%). I was expecting the exact opposite to occur. I was expecting circuit B to be silent because the inputs are perfectly balanced (in theory) and was was expecting circuit A to have some noise (thermal or RF) on it's output because the inputs are not balanced. Please disregard the strange apearance of the circuit. It is the preamp of an audio amplifier and the mic is not shown. I stumbled across this behavior while experimenting with eliminating noise from the mic circuit. Also, this circuit is built on a 4 layer board with a ground plane and good noise immunity and the op-amp is powered from a split supply of +/- 9v.
I welcome any discussion on this. Thanks in advance.
I welcome any discussion on this. Thanks in advance.
Attachments
-
17.5 KB Views: 42