Post pics of your builds.... - Page 433

sometimes, proximity has a strange way of causing problems.

it sounds counter-intuitive, but I've seen it happen. move wires around and watch the spectrum (or listen for hum). I keep saying 'wire routing MATTERS' and I'm not at all kidding.

I went thru at least 3 b22 layouts (on wood mdf) before getting one that was hum free. and the trafo was on the floor the whole time, via a long wire away from things.

I'm not kidding. I can't fully explain it but I have experienced it enough to not just take things for granted. I don't run 'power' near 'signal' and especially if its an input to an amp. even in car audio, they teach the same basic idea (run power down one side of the car and audio runs down the other).

Yes, proximity to something with 60Hz AC on it, which encompasses the mains wiring, transformer itself, and the output wiring from the transformer. You're essentially saying a low current DC power wire can generate a strong 60Hz EM field on its own.


Just putting the transformer on the floor doesn't remove proximity from all AC wiring, so I'm not sure how that has is supposed to support the idea that DC wiring will induce hum on signal wires.

I would think grounding issues (or lack of a ground loop breaker) would be a more probable cause of humming than noise on the DC lines being induced on the input lines.
Specially considering the quality of the power supply used (assuming you used a sigma22).

Very true. 60 Hz hum comes from AC and AC alone. No way to induce it with DC current.

you guys can argue 'theory' all you want; it doesn't change how things are.

I can't explain it but I have experienced this. your theory is trumped by actual experience, though.

in a car, the battery is still 'DC' and yet hum is picked up by the power line (alternator) and DOES get into the signal when you run power and signal next to each other. its a fact, ask any car audio installer.

same thing happens here. you can argue all you want but that does not change what happens.


whatever....

Yes, but your car also has much higher currents, and doesn't have a sigma22 power supply.
If it did, I doubt you'd pick up any noise on the DC lines.

As I said, hum might also be caused by grounding issues, which I think would be more probable than AC noise on the DC lines.

And a car's alternator is an extremely noisy power source that usually corrupts the ground. Also a car has a high voltage ignition system that also adds to the noise floor.

Here's the results of a quick test of linuxwork's theory of DC wires spontaneously generating 60Hz hum, the results will shock and astound you. I set up the signal wire with an unshielded segment about one foot long in the "test area" and the rest shielded.

Function generator was set to 1KHz 1mVpp to simulate a very weak audio signal:




Any 60Hz fundamental present is buried in the noise floor:




I wadded up about 25 feet of wire and mixed it in with the unshielded part of the signal wire, then put 1A of current through it. Hmm... still not getting anything at 60Hz:




Unhooking the input wire and leaving the spectrum analyzer's input floating, now that gets a small amount of 60Hz hum to show up:

So it's the background noise of the universe? That sucks.

Finally we are able to tap into the ether.

I can't say I'm astounded.

An auto alternator is a A/C generator with a simple bridge rectifier to produce DC. The Sigma22 (or any good DC PS) has a bit more going on to filter the ripple

Not that I know anything of car audio.

As someone who fashions themselves as contributor to the community you have a horrible attitude.

What if I said I was naked the whole time I did the tests?

Yeah about that...