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Does 'Dirty Electricity' Exist?

#41
I dont see either of these scenarios- higher voltage or lower voltage thresholds being reached without some sort of egregious human error. That being said, in my own home, i had an issue that blew my mind. Basement lighting fuse - four ceiling lights, one outside light, eight bathroom lights on a wall, a light leading up the steps, several outlets with nothing plugged in started blowing. Townhouse built in 1998, this was in 2019. I attributed it to the strip in the bathroom- there was a broken bulb in it. I went to replace the strip, noticed that the switch was only drawing 48 volts. The cause was the switch to the outdoor light. Someone- either the original electrician or the previous owner who moved out in 2000 had ganged the hot runner and the outdoor light on a single screw tab on the outdoor switch. Clearly not up to code. The hot to the outdoor switch had worked loose somehow and was arcing. The switchplate cover was warm to the touch, the switch had actually melted. Luckily there was no fire. This switch had been wired in this fashion since at least 2000. Why it took 19 years to show up was ponderous. Im guessing that opening and closing the sliding basement door which was inches away from the switch had vibrated the wire from beneath the ganged screw tab on the switch. I hadn’t used that door in over a year, it was actually blocked off with stored boxes that had been there for quite some time. Agedhorse accurately pointed out that it is nearly impossible to point out the root cause of some failures without really digging into surrounding conditions, and this is proof of that. Never in my wildest dreams could i think that out of the clear blue could what i have described be possible, but there it was. I count myself extremely fortunate. Heres a shot of the switchplate- the blackened soot is visible above the switchplate.
 

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#42
turf3 said:
Most equipment is certified to operate at +/- 10% of nameplate voltage. So if it says (for example) "100-120VAC", you should be able to expect that it will operate at 90VAC. It all depends on what's printed on the nameplate.

This is distinct from "dirty" mains voltage which is non-sine-wave voltage. That is very common when a circuit is shared with high power switching power supplies of dubious quality.

In theory an audio amplifier ought to have in its DC power supply sufficient isolation to allow it to tolerate "normal" amounts of noise in the mains power. But I don't know what the "normal" amount would be for audio equipment.

It's pretty easy to measure mains voltage, but it takes much more serious equipment to accurately measure noise in the mains supply. Some multimeters that claim to be "True RMS" will have a power factor measurement, and if you put a pure resistive load (electric heater) on and measure PF, that'll be an indication of how noisy the mains supply is. But not all meters that claim to be "True RMS" really are (I can't remember my sparky buddy's explanation for this).
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Measuring power factor requires both a voltage and current measurement simultaneously.
 
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#46
mapleglo said:
It could also be you are coming close to the max that the one outlet can supply as far as current is concerned, which may be dragging down the voltage slightly.
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This happened to another band I was in when we were outdoors, and the venue only had a single extension cord for us. The PA would occasionally crackle and sputter.

BTW- I've continued to test my Ashdown amp and can't reproduce the noise at home. The venue we played hosts several food trucks and I'm sure they provide electricity for these vendors.
I ordered a Volt Test Monitor that I'll bring to the next gig. It's a small laidback venue, and we don't have to cover a lot of area. We're on their rotation to play several times during the season, so I'd like to keep playing there.

Thanks to everyone for the advice... and 'dirty' jokes. ;)
 
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#47
I have some experience in analyzing the quality of the AC power at sites where we were installing very sensitive diagnostic medical imaging systems in locations, (in under-developed countries, outside of the US) where the grid was known to be unpredictable and tested the power because problems were anticipated. We would find problem situations and engineer custom power conditioning equipment to compensate.



A little pricey for checking the power in a dive bar, but it would be effective.
 
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#50
They make a device called a Power Quality Meter (PQM) for this type of thing. We use it to look for harmonics in the power grid if our equipment is acting strangely while connected. (Large Scale Solar inverters)

It will show you the 3 phase sine wave and any irregularities will be obvious.

kgb
 
#53
jimmydean said:
There is a wiring issue at the venue , usually something is not grounded properly . You can try a noise gate pedal like Electro-Harmonix Hum Debugger .
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I've got a EH Hum Debugger. I'll bring it next time. Thanks!
I'll try everything and try to eliminate all the variables.
I'll also ask some of my buddies who play at this venue. I think they're bass player uses an old Peavey.
If an old Peavey works, I could just buy one and leave it there. ;)
 
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#57
agedhorse said:
A short term solution...
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Quite true, but as @6thplanet said, sometimes that's all you need, and maybe all that's available. I played a gig a little while back at a nice room where for some reason my amp kept making this hum that I've never heard it make elsewhere. It was really bothering the percussionist sitting right in front of my cab, who kept looking at me as if I could fix the problem, which I couldn't. Fortunately, the sound man had one of those E-H Hum Debuggers, and it worked well enough to get us through the evening.

Obviously, it's not a long-term solution. The very fact that the sound man had this thing so readily to hand tells me that I probably wasn't the first person to have this problem in that room, and wouldn't be the last. There was almost certainly an underlying issue that needed fixing. But in the moment, that more fundamental issue wasn't gonna get fixed by showtime, so the temporary solution was quite welcome.
 
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#58
To OP, yes, dirty nasty power exists. Never trust a venue. Make sure you have a Power conditioner as 1st line of defense and a Furman surge protector as a 2nd line of defense. It does not seem a lot when you sit down and figure what you have invested in equipment.

Some here will tell you I am silly. Not an issue in 6+ years. No noise, no blown equipment. Best offense is a good defense.
 
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#59
Parzival said:
To OP, yes, dirty nasty power exists. Never trust a venue. Make sure you have a Power conditioner as 1st line of defense and a Furman surge protector as a 2nd line of defense. It does not seem a lot when you sit down and figure what you have invested in equipment.

Some here will tell you I am silly. Not an issue in 6+ years. No noise, no blown equipment. Best offense is a good defense.
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Yet most of those devices are virtually useless in addressing this problem, and provide virtually no protection beyond what’s already built into the amp.
 
#60
agedhorse said:
Yet most of those devices are virtually useless in addressing this problem, and provide virtually no protection beyond what’s already built into the amp.
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They’ve worked 100% for us. If it’s snake oil? It has worked. And we’ve played some shady joints. No less than 2 have burnt down.

I assure you I wouldn’t plug my gorgeous Subway D800 into any old honky tonk power.
 
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