I just don't understand HUM

[aron]

What causes it? How does it happen? When is hum really BUZZ? Is BUZZ different from hum?

Let me start out by saying that hum and buzz have been the primary factors that make or break a lot of circuits for me; including my amp circuits.

Here's what I have heard for possible problems with hum:

Check grounds. OK, I have heard that sometimes hum is introduced if a pot is not grounded correctly.

Now I don't understand this. If a pot is not grounded "well", then either it will be some infinite resistance (acting like the pot is out of the circuit) or not, or somewhere in between right? Now would this add hum? Does it add hum because now the pot is acting like it's out of circuit and therefore the tube/transistor has too much signal because it doesn't have a load?

Same for a cathode/source/emitter ground. If there is no good ground connection, wouldn't this introduce loss of gain and therefore, less hum?

OK, for input and output jacks, yes, I have heard grounding problems so I understand this part.

Finally, I ask because I'd like to understand this more.... I suspect it has more to do with CURRENT vs.... what I am thinking of.

Take for example this circuit:



I have not been able to stop the horrendous hum from this circuit.

It's so simple, yet there's incredible hum. I've built essentially the same thing with Tim E's super class A circuit and his circuit works fine. Why does this one hum?

Finally, is buzz similar to hum? I can't figure out you know when buzz is not really hum with additional harmonics introduced.

I had my Camacho amp and I tried EVERYTHING! Single point ground, shielding, layout, etc.... it buzzed like mad.

Drove me nuts.

Experts, please chime in.

Thanks!