electrical issue - dimmer switch causes amps to buzz crazy

I have a ceiling light plugged into a wall outlet that is controlled by a lightswitch.  I changed the lightswitch to a dimmer, and now whenever I use the dimmer, my guitar amps start buzzing like hell.  If I switch the light to a regular outlet, there is no buzzing.  

Now, I know that this is a very common thing, and it is not important to me to be fixed (as is said, I can just plug it into an outlet without a dimmer).

It would be great if somebody could educate me as to how and why this occurs  

The dimmer switch works by interrupting the AC cycle of the supply very abruptly part-way through a cycle, every cycle. The position at which the interruption occurs varies, according to where the dimmer's dial is set. The effect of this is to reduce the amount of power getting to the light itself during the cycle, which in turn reduces the intensity of the light. It switches back on at the start of the next cycle, and then gets cut off again - and it does this every 50th or 60th of a second (depending on where you live).

The interference buzz is caused by that very abrupt switch-off - this has harmonics that extend all the way up to radio frequencies, and they get radiated into anything that's not adequately screened or earthed. Obviously, the higher the instantaneous value of the supply wave at the point it's interrupted, the more interference gets generated - which is why it varies somewhat according to what level you have the light dimmed to. What this generally means is that at low settings, you get a small amount, mid settings quite a lot, and high settings not so much again - but the effect of this can vary, and you won't neccessarily hear it quite like that.

it does this every 50th or 60th of a second (depending on where you live).

100th or 120th, as it does it on each half-cycle.

This noise source, of course, is why high-quality balanced cables are a good idea when running mic cables through the ceiling of a hall or theatre  

Paul

it does this every 50th or 60th of a second (depending on where you live).

100th or 120th, as it does it on each half-cycle.

Quite true, but this was the English explanation - and most people know that the AC mains frequency is 50 or 60 Hz, so I left it at that...

It would be great if somebody could educate me as to how and why this occurs

Well, we've done the 'how', but the 'why' is much harder. I have no idea of why you are using a dimmer that buzzes!

Filter that bad boi!

Filters are increasingly seen as something that can be done without from a mfgr's POV, since it cuts into the bottom line, although to hear them, "explain" it, one would think that these additional "elective" components would actually decrease the reliability of the product <shakes head, sighs>.

Filter that bad boi!

The real problem with this is that if it's to be truly effective, the required filter is going to cost way, way more than the dimmer switch...

Maybe some informative reading on this issue?

Maybe some informative reading on this issue?

What Ethan appears to describe is a much better way of dimming the lights - use a variac! This is effectively a variable auto-transformer where the variable tap is controlled by a big rotary knob. It doesn't cut the waveform up at all, so it doesn't introduce a load of buzz.

While installing variacs as dimmers might work if you have sheetrock walls, I'm not so sure it is a good move in traditional brick buildings. Other possibility is to opt for HF dimmers. Or install more low power lights.

standardized candles

While installing variacs as dimmers might work if you have sheetrock walls, I'm not so sure it is a good move in traditional brick buildings. Other possibility is to opt for HF dimmers. Or install more low power lights.

I think that the whole thing's a bit of a joke, actually - never mind the state of your building. Have you seen the price of variacs? The cheapest small one you can get is about $75 or thereabouts. The economic practicality of using them for lighting control is not too great at all!

I changed the lightswitch to a dimmer, and now whenever I use the dimmer, my guitar amps start buzzing like hell.    

Just about the worst scenario -- an electric guitar being a high impedance, low level, unbalanced, inductive input!!

Reminds me of the fiasco with the introduction of the CE immunity standards in the mid 1990's --- because the electric guitar was not in a specific category, it was expected to conform to the overriding 'generic' standards, and to conform to those, it would cease to function as an electric guitar!!

Ahh - the wonders of EU regulations!