they are the most sensitive to RF interference (hum) because any induced RF EMF will be amplified along with the input signal.
Always good to shield the source.The Shielded AC line option is still an option the I am considering. I just think it might be messy at the junction were the thermo wires come up to the lateral run at the top of the chassis?. I am going to spend a little elbow grease with some steel before I stress the AC wiring with un-soldering.
I do agree with you that it makes sense to shield the source of noise rather than the receiver, but I have a 'shoehorn' idea that is fairly simple.
I will post picks if I have any luck
You can lead a horse to water...
Peter, one last try and then I'll keep my mouth shut.
First, what's so stressing about desoldering? Piece of cake if you have some solder wick and perhaps a solder sucker. About a 15 minute job and most of that is waiting for the iron to heat up.
Twisted pair shielded is really your best option - just sayin'. Buy some of that shield twisted pair recommended earlier - great stuff. Shielded twisted pair is likely to be smaller and easier to tuck than what you currently have. You only need to ground one end of the shield (actually that's best anyhow). You can run the ground for the shield to star ground point. Here's a picture:
Glad I got that off my chest - I'm starting to feel better.
View attachment 39707
Hi Jim;
Sooner or later, I will need to 'drink the water'! I really appreciate the advice and I'm glad that your input is on record in this thread. When doing it 'my way' fails, as it usually does, I will finally have to do it "The right way". I had initially considered shielding the AC wires, but Henry Ott's book says that non-ferrous shielding has no effect on electromagnetic radiation, only electrostatic.
Admittedly, I believe the issue to be capacitive coupling between the AC hot wire and the control board, so copper shielding would help.
I am pursuing my crazy steel box for the control idea because of a (quite possibly hair-brained) theory that when the amp is driven harder and more current flows in Hot and Neutral AC lines, magnetic radiation will be more of an issue. Of course the hum would be harder to hear behind a large signal but still.........I could be all wet here.
Anyway, my steel box is half finished and it will work or I will toss it, and move on to your proven methods.
Thanks All, for your valuable help.....and patience.
PS; Test results to follow asap, but wife telling me to get some work done!
Of course, you are technically correct. But, what we have here is 60Hz hum "radiating" through space to another wire or component. Spare us the nomenclature about frequency bands, the effect we are talking about is RF as in radiated AC signal, (transmitter and receiver) thus RF. If it were conducted as in wired AC signal or inducted as in wired DC signal, (microphone and speaker), thus AF. So, no.I generally agree with the recommendations you give, but RF is defined as 20kHz to 300GHz. What's being coupled into Peter's system is AF - audio frequency - noise from the 60Hz AC line.
Peter - you can put a dead short across the audio input lines and do no harm.