My new basement is filled with dimmers!


The stuff in my rack works just fine, no noise, but all guitar amps hum like a hive of bees, and IIRC this is symptomatic of dimmer switches - and the basement is filled with them. What should I do?

Gad - hope I don’t have to replace all the switches. Would a ground loop isolator like HumX help?

Hum X at Sweetwater:

It might help Tom. Unfortunately, I doubt if that will be the cure all though. Some dimmers operate by actually clipping the AC sine wave and this generates electrical noise as well radiating RF noise into the surrounding environment. I’d try a little experiment. Plug in an incandescent floor lamp so you won’t be totally dark and then kill all the other lights on the dimmers. Turn them OFF, don’t dim them all the way down. Go all the way back to the breaker box if you have to. With all the dimmable lights dead, does the noise go away? I’m betting it does and unfortunately, you’ll need to replace those noisy, RF generating suckers with newer dimmers or good ol’ switches.


Yeah, if it’s a cheap SCR dimmer there only one way to kill it – Replace the dimmer. It could something else, but finding the source is the thing and that’s not always easy.

Try what TG suggested as replacing switches is a very cheap and permanent solution assuming they are the culprits.

Well, I don’t think my wife wants me near an outlet with a screwdriver. You know, I went to the same high school as Tim Allen. Truth. Birmingham Seaholm. :)

'course, I never made it big as a comic, so maybe it’ll be OK.

OK, will they swap out just like a normal switch? I’ve changed normal switches.

I’m going down to try your experiment, Dio, right now.

Thanks, fellows!

Just to make clear what Diogenes said:

Some SCR’s generate interference that is transmitted like radio waves - you don’t even have to have your audio equipment physically connected to the same circuit with the SCR to pick up the noise.


Yep, they use the same wiring as regular switches, but some are hooked in with pigtails instead of screws. The tricky ones are the ones made for three way switches. You’ll do fine as long as the power is REALLY REALLY off.

Keep in mind that any dimmer on the same service may be causing it, and it may not be a dimmer at all. Motors and other electronics can introduce buzz into the lines.

Plus, are you sure it’s buzz, as in dimmer kind? It could be a ground loop. If that’s the case then the isolator may do the trick. On way to figure this out it to make sure the amps are all plugged into the same outlet, as an experiment. If an amp it plugged into an outlet on one wall and something else is plugged into another outlet in the same room or a different room then the two outlets may be on opposite sides of the service. That SHOULDN’T happen in a single room, but I’ve seem it and experienced the trouble it can cause.

And, are the outlets REALLY grounded with three wires? An old house I had in NC was wired with two wires and the electrician used a jumper to short the AC ground leg (white wire) to earth ground (green wire - usually). That’s a major no-no, but he did it anyway, and the first time I plugged in my stereo after the “rewiring” I almost blew out my speakers. The outlets on opposite sides of the room were on opposite legs of the AC. That causes a DIRECT ground loop of 220 volts from one side of the room to the other. To say that was dangerous is an understatement. Ummm…I called the electrician back and had him redo all the wiring correctly. He didn’t charge a cent for the redo fortunately. I’m lucky no one got zapped.

Quote (TomS @ Nov. 14 2006,13:46)
OK, will they swap out just like a normal switch? I’ve changed normal switches.

Yup, it should be a one for one swap. Kill the breaker, remove the dimmer, there are two screws to unscrew to remove the wires, then put in a new switch and wire it the same way. Just be sure the ground screw goes to ground and not the circuit. It should be pretty self evident once you get the dimmer out. Just be sure you kill the power at the fuse/breaker box as you don’t need any surprises.

Phoo, that sucks. It is better no ground than a bad ground. That is how folks get killed. My grand pappy almost bought the farm from the once. A improperly connected ground and a busted steam boiler…


If they are indeed SCR dimmers, they generally emit MORE radiation when the light is dimmed to it’s fullest (but not off) The noise is a very harsh rasping buzz, very distinctive, not like mains hum at all.
Proper filtering and shielding can help, but the best way to go is just to replace them.


Well, there is a ground loop problem and dimmer buzz, AFAICT. We had an electrician go over the house before we bought it, and the basement had been set up as an apartment about 10 years ago, with every plug being of the ground fault variety. Everything was wired and grounded correctly - except for one plug that was installed by a weekend warrior at a later date, which is not in this circuit. So we’re going to hope that something like HumX will take care of part of the problem, and replacing the dimmers will take care of another part.

I’ve spent so many years learning just the right angle to stand when playing the strat anyway, so a little hum is part of the music to me. :D

Beefy - you have described it perfectly.


Phoo, that sucks. It is better no ground than a bad ground. That is how folks get killed.

Yes, and THAT is why he didn’t put up much of a fight when it came time to redo his sloppy and illegal work. He was probably glad I didn’t turn him in, and I was a slug for not doing it.

Yep, Tom and Steve, that discription sounds JUST like dimmer problems. One anywhere in the house can do it.

Anywhere in the house? There is one more, in the dining room. Are there any dimmers that won’t cause a problem? I saw some pretty cool digitally controlled dimmers at the hardware store the other day. Would they work?

The SCR kind will introduce the buzz directly back into the AC wiring, so anything on that leg of the power can pick it up. That’s the principle that some home automated dimmer controls work on (DX-10?? Was that a brand?). They broadcast the control data directly into the wiring in the house so all you need is a little module that plugs into the outlet and whatever is being controlled plugs into the extra modules. Modules not on the same leg won’t pick up the data and won’t work. They don’t work by broadcasting through the air. That’s also the reason a dimmer in your neighbor’s house won’t bother your stuff usually. Also, the RF for those control things is high so it it doesn’t usually interfere with normal AC use. Good power supplies will easily filter out that kind of RF.

Cheaper SCR Dimmers on the other hand put spikes in the AC that even good filters can’t handle. They literally hack the AC sine wave into bits, so it’s not a sine anymore. It’s a very nasty way to lower power…it doesn’t strictly lower the voltage though it can. Think of the way an amp clips the sound by hacking the top and bottom off of the wave…adding horizontal flat spots. An SCR will hack the wave up by putting vertical cut-offs.

Some dimmers use a different king of circuity so they don’t buzz as bad. I don’t remember offhand which ones. It’s been a long time since I looked at them. I suppose they would say on the packaging. It’s probably safe to assume if it cost $7 it’s going to buzz. That doesn’t mean a $30 dimmer won’t buzz of course. The digital ones may do ok…may not.

Sorry, that’s not a good answer is it? :)

Tom, that HumX doohickey sounds as if it’s just a filter. It’ll help, but it’s sure better to have a good studio ground in the first place. And that means one good solid ground, and all the other ground connections radiating from that in a star formation.

And yup, get rid of the dimmers, and the beer refrigerator too while you’re at it. :)


(DX-10?? Was that a brand?).

Yup Phoo, I still have my Yamaha DX-10, a wonderfully dirty FM synth, (never dimmed no lights with it tho’ :D )

I tell you Tom, NOTHING works so hard at removing the joy out of a new toy (or in your case studio) than having some problem that you didn’t expect and can’t ignore…

Good luck in sorting this out.
I hope it is quick and easy

HA!!! It wasn’t DX10 – it was X10. Close, but not quite. :)

EDITL Found something better…

Get rid of the beer fridge! wash your mouth out with soap and go to your room! Geez, Gizmo, what are you thinking?

Hey, Phoo, what does SCR stand for?

Super Crappy Rheostat … err, I mean, Silicon Controlled Rectifier

However, if you really really really want dimmers, look for something that is variac (or autotransformer) based dimmer. That is what the big boys use in pro studios when they want to be able to do the whole mood lighting thing. Oh, and how does a second mortgage sound?

Just a thought, but you could try using an uninterruptable power supply (UPS). Here’s a couple of links:…anchor1

Note that this UPS conditions the power, so it should eliminate the problem you’re experiencing.