I've made some progress on solving the cross-talk and the 'clicking' from the Chancel speaker when playing MP3s of church music. The attached drawing is an updated version of the Audio and Solenoids Circuit which represents the current state of play. The differences between this version and the one that was deployed in April of last year are that:
- I have added 'Audio Conditioning Circuits' to the inputs of the Audio Power Amplifiers. These:
- Isolate the O/P of the driving device (Pi Audio jack or USB Audio Adaptor) from the Audio PA I/Ps.
- Pot down the I/P signal to bring the levels into a range to suit the Amp I/Ps. (There was some potting down originally, but this has improved on that.)
- Add a series resistor to help match the signal. (I'm not sure these do much but having put them in, I'll leave them there.)
- I have added a PSU Filter Circuit to reduce the ripple on the incoming 12 V, which was much worse with the replacement PSus that were fitted in August than the originals.
Over the next few days I'll install the filters into their final positions and shorten the wiring as much as possible to see if I can reduce the hum still further.