[Matt]

Hi, all.

I have an EarMax Pro which, as it warms up, starts to hum and I *desperately* need and could use some help from anyone and everyone in the know.

I've done some scientific evaluation and have determined the following:

1. As the two, side tubes start to steadily glow, the hum "fades in." (I guess these are the "output tubes"?)

2. As I turn the volume of the amp up or down, the hum does not increase or decrease (it stays static).

3. As you know, when you turn the power supply off on the tube amp, since the tubes are still glowing, music still comes out, but fades away. With this amp, if I turn the power supply off, the music stays-while-it's-fading, but *the humm goes away instantly*! (I am guessing this means that the power supply is not filtering out power line noise).

4. As I move from room to room in the house, the humm changes in volume (more upstairs, less downstairs...in fact, very little downstairs).

The only thing I can glean from these facts is that it's not the amp, and since it changes from room to room, I'd assume that it's some sort of filthy power upstairs.

If that is the case and the power is filthy, what can I do to (economically) filter this noise out? I can't afford to splash out hundreds on a line conditioner, so are there any cheap(ish) solutions to this problem? If it only handled the humm, I'd be grateful.

Is there some sort of RadioShack regulated/filtered unit which has a standard female plug jack thingie on it, so it would feed off the regulated/filtered power?

- Matt

 

[Nick Dangerous]

Gotta rule out RF interference, too. I had a NASTY problem with that at work. Some device in the power stream made a steady high-pitched beeeeep beeeeeep beeeeep in my right ear last night no matter where I plugged it in.

I had to do the old TV console dance to keep it quiet. You know... stick out my left arm, balance on one foot, wiggle my toe... that's it! Hold still!

 

[JML]

It could be EMI/RFI or a bad power outlet/circuit. Identify the problem before spending money on a solution. Here are some cheap ways to check:

First, check that the outlet you're using is properly oriented and grounded. That means hooking up a multi-tester to the outlet or using an electrician's outlet checker for a three-prong outlet. If it isn't correctly wired, +/-/grnd, and many are NOT, you may have found your problem (check every single outlet on that circuit -- one miswired one can be the problem even if your amp is not plugged into it!). Second, get a long heavy-duty extension cord, and try reorienting the unit physically within the room (checking to see if the hum changes as you reorient the amp and move it around the room to change reception of the radio waves that can cause RFI). Also try plugging the amp into other outlets in your home that are not on that circuit (i.e., turn off the breaker first to identify all the outlets on the circuit) and also try unplugging all the other things on the circuit (it could be some other appliance that's the source of the noise, and you can find it by plugging things in one at a time -- it could even be a light fixture or a dimmer switch, or even an array of wiring in an adjacent wall).

I'm going to bet the problem is a faulty ground connection. Good luck -- I had an RFI/ground problem that drove me nuts until I figured out a cure.

 

[Matt]

...thanks for the help.

I don't think I have any of that equipment. Erg.

As far as moving it around the room goes, I've tried different jacks within my room and they all do the same thing. I took it downstairs, though, and it was fine.

Erg...I'm not too keen on dicking around with power outlets. Will it require turning the breaker off and all that?

I bought a RadioShack AC line filter (the $14.99 one). Poo. I thought that would work (haven't tried it yet, but based on these responses, it looks like it might not work [?])
Erg...a pain, this is!


- Matt

 

[JML]

That filter is worthless. I just tried it last week.

Either being higher up in your house has changed the radio wave environment, or the circuit into which you're plugged is bad.

You should have the two electrician's toys anyway. The outlet tester is about $10 at Sears, Lowes, Home Depot, etc. A decent multimeter can be had for $25 at Sears (you don't need more than that).

Don't open the latter unless the first shows a problem. The solution to a miswired outlet is as simple as turning off the power and swapping two wires. I'm sure you can do that! The multimeter or a separate AC tester is so you can be sure that when the circuit breaker is off, the power is truly off. Don't trust the circuit breaker, or even the outlet tester. Miswiring can cause the power to be turned off, but a wire to the outlet might still be hot, and we don't need to lose a Head-Fi member.

The AC tester or multimeter would let you confirm that there is indeed no current in the wires before you touch them.

 

[Audio Redneck]

Matt,

JML is right about turning off the circuit and seeing what else is on it. What else is on that circut? First thing I would look for are floresent lights (like those energy saver bulbs). I would then look for high powered equipment (computers, electric space heaters, old TV sets, etc.). Be sure you have everything-else on the circuit turned off. If the problem goes away, turn things on one at a time until you find the culpret.

Check with some of your friends and see if any have an APC or Tripp-lite surge protector with a Fault indicator light and borrow it for a few hours. Just plug it in and if the Fault light glows its telling you your ground isn't connected.

Good luck

 

[Matt]

Hi.

Tried the APC thing...fault light stays off.

Tried unplugging stuff around the room...humm still there.

Alright, so does this potentially mean a hunt around the house for a single offending socket that is mis-wired? I am dreadfully new to this...what can I realistically expect as far as hunting and fixing goes?

Thanks again for helping me through my ignorance.

Best,
Matt

 

[JML]

Go to the box with all the circuit breakers. Turn off the one that controls the outlets in that room. Then see if any OTHER outlets or appliances are also off. Wiring doesn't go by room, it goes by electrician's whim and ease. You can have three circuits in one room, and one circuit for two and a half rooms, and any other combination imagineable, especially if the house is old and any rewiring was done over the years.

One miswired outlet on a circuit can cause a noise problem. Or one item plugged in. No solution other than trial and error. You might also try reversing the orientation of plugs if they're only two prong. The three prong are polarized for safety, but a two prong can cause noise if it's reversed and the audio equipment is sensitive to noise. A multimeter will let you determine the best orientation (I can send you a link to directions).

So check all the outlets on the circuit with that APC. What you're doing is the same thing as using the outlet checker I recommended.

If this doesn't show anything, then you may have EMI or RFI from a non-obvious source. These are bigger problems, and less susceptible to diagnosis and fixing. EMI could be from something else on the circuit, from wiring in the wall, or cable TV cabling, or from proximity to something electrical (it could be a cable or transformer hanging outside the house, or the the wiring coming from a utility pole). RFI is from radio, and a real pain to diagnose and cure. My tonearm turned into an AM radio antenna when I moved it about fifteen feet in my house (same floor, same orientation. same height). I had to work on grounding solutions (from tonearm to chassis to amp to house circuit) to cure it. If you have a portable AM radio, try moving it between the locations in your house and see if it changes what it picks up, and then put it near your amp and see what happens. If the hum gets louder, you have RFI problems. The inexpensive solutions for that are grounding, cable shielding, and ferrite cores on cables.

Have patience!

 

[Matt]

Holy cow. I will conduct this experiment next weekend and tell you how it goes. I've got to get everyone out of the house first! Gee, boy, I'll get this problem solved yet...

Thanks so much for the info, it is much appreciated.


Best,
Matt