Where do we start? “I want to run an audio line from a sound module to the mixer of a speaker-amplifier. Usually I simply run a shielded cable with a banana plug on the module side to an RCA plug on the mixer side. Someone suggested that I install a transformer at the output of the module to achieve a quieter transmission. I really do not understand this. Could you explain?
Well, first I am amazed if you are really using a banana plug at the output of a module. I presume you mean a 1/4-inch connector. At any rate I would start by asking if you have a noise problem? I just hate it when people go around and muddy up the waters by trying to fix something that isn’t broken. If it’s working okay for you leave it alone. If your system is noisy the next thing to do is to prove that the noise is coming from the line. Try temporarily moving the module closer to the amp and running a shorter line. Also, check for ground loops. If you prove that your noise is caused by the long unbalanced line then you may benefit from a transformer. The issue is that unbalanced lines like what you seem to be using do not transmit over long distances very well. The exact length an unbalanced cable is effective will depend upon many factors, including impedance issues, but for audio a general rule is that if your cable length is 20 feet or less unbalanced is usually okay. Balanced lines have much better rejection to interference induced along a cable length. One effective way to balance an unbalanced signal is to run it through a balancing transformer. Of course it must go through another similar transformer at the other end to unbalance it for connection to the unbalanced input on the equipment. So you actually need two transformers, one at each end of the run. This is not hard to do and it will clean up dirty unbalanced lines. Another trick that might help was detailed in yesterday’s TTOTD.