Bad House Power Causing Bad Tone?

[Daver]

Is it possible for bad power from the outlet to cause unusual tonal artifacts? In the last couple of days I've been prototyping a couple of similar amps. There's been this little "sweet" artifact that you can sometimes hear around the note. It's far more pronounced using an overdrive pedal. That's where I first noticed it. After tearing my hair out trying different circuit tweaks, tubes and speakers I tried my other amps. Holy Crap! They do it too! There's this extra harshness with the tone that wasn't there before. It happens when the pedals are powered from a One Spot, or a battery or if they're used by themselves with no other pedals in line. I can hear a bit of it when the amps are clean. The AC tonight measues 123 volts. A little high, but it's around 120 other times I've measured it. So, can the AC coming in have this affect? Is there a way to test for it? Thanks.
Dave

[Jazz P Bass]

First, rule out any extraneous noise inducers.
Triac lamp dimmers are notorious for putting crap on the line.
Space heaters are another good one (and window air conditioners).

[Daver]

I have no dimmers or space heaters. I have central air but it's in the 30's here, so it's not on. Nothing in my home has changed. This is something new in the last few days. It's weird! Thanks!

[olddawg]

Do you have a scope? You should be able to see it on the line voltage. Once upon a time power transmission was done exclusively with KV AC. Nowadays, more and more, they use ultra high voltage DC and have monster inverters at the endpoint. The reason I have been told is that they can run more current through the same sized wire. This is a big advantage if you have a growing population but do not want to add more infrastructure. But you don't get anything approaching a sine wave and there are artifacts galore. Have you tried using your amp in a different location. I used to play a club that was notorious for crap like that. There was a giant gas station 10 ft away from the stage back wall.

[Steve Conner]

I suggest buying or borrowing a variac. You can apply any line voltage you want and see how your circuit responds. If it sounds great at 120 but lousy at 123, maybe it's on the verge of oscillation.

Speaking of monster inverters: Being a power electronics geek I just bought one of Panasonic's "Inverter" fridge freezers. Unfortunately my workbench is close to it in the kitchen, and it injects a loud whine into my experimental audio circuits.

In HVDC transmission they take filtering pretty seriously, with "harmonic filter yards" that take up the best part of a football field. The mains has to have less than 3% distortion by law.

[g1]

Can we assume you have tried other guitars/cords/pedals, to rule out anything other than your amplifiers?
Next step would be to try one of your amps at another location. Some kind of noise on your house power does not have to come from your house, it could be someone else on your street, some new business/industry started up near you etc.

[olddawg]

I suggest buying or borrowing a variac. You can apply any line voltage you want and see how your circuit responds. If it sounds great at 120 but lousy at 123, maybe it's on the verge of oscillation.

Speaking of monster inverters: Being a power electronics geek I just bought one of Panasonic's "Inverter" fridge freezers. Unfortunately my workbench is close to it in the kitchen, and it injects a loud whine into my experimental audio circuits.

In HVDC transmission they take filtering pretty seriously, with "harmonic filter yards" that take up the best part of a football field. The mains has to have less than 3% distortion by law.

There are laws for water quality, pollution, etc. Doesn't guaranty compliance. Scope your line voltage in a city sometime. There are artifacts galore.

[Chuck H]

I suggest buying or borrowing a variac. You can apply any line voltage you want and see how your circuit responds. If it sounds great at 120 but lousy at 123, maybe it's on the verge of oscillation.

Speaking of monster inverters: Being a power electronics geek I just bought one of Panasonic's "Inverter" fridge freezers. Unfortunately my workbench is close to it in the kitchen, and it injects a loud whine into my experimental audio circuits.

In HVDC transmission they take filtering pretty seriously, with "harmonic filter yards" that take up the best part of a football field. The mains has to have less than 3% distortion by law.

Looks like you'll need to build a Faraday cage around your work room!

That 3% line distortion law is pretty awsome. olddawg may be right, but I'm inclined to think the real noise issue with this method of line power is in the units that make it back into AC for the dwellings.

I've only seen this kind of line power used in newish "homeowner communities". You know, the kind of places where there's a rows of two story houses so close to each other that there's no yard and the whole thing has a big fence around it with a code lock gate. Lots of hash on the mains in these places. Lots of problems in these homes with modern electronics that are sensitive to it. This is in California where I use to live. It's probably improved in the last fifteen years.

[Steve Conner]

My lab has always been in some office block or university campus in an industrial city. Yes, the mains is dirty as hell. I have seen 10+ volts of high frequency hash on it, playing havoc with sensitive experiments. But it's not the utility's fault, it comes from all of the power electronics on the consumer's side. Server room UPSs, inverter driven HVAC plant, that kind of thing.

I've worked with engineers from the power company to track these things down, and they always ended up being on the low voltage side. I've seen power quality data from the 11kV side and it's really quite clean.

Grounding the fridge door seems to help quite a lot.

[Daver]

Thanks for the help, guys. Yes, I've used different pedals, cords, guitars and amps. I'll have a chance to try an amp at a different location this weekend. My house is in a residential area and was built in 1923. To the best of my knowledge nothing has changed in the area. I will put a scope on the AC tonight and try a variac to lower the voltage, although I don't think I have an oscillation becaues it happens in all my amps. I'll report back. Thanks!
Dave

[R.G.]

I did some thinking for my articles on mains power for guitar amps in Premier Guitar.

From that, there is one solution that's available to you and is pretty much slam-dunk. Get a harmonic neutralized constant voltage (ferroresonant) power transformer big enough to run your audio gear.

Ferros have some drawbacks, among them being mildly expensive and heavy. But other solutions to mains pollution with equal effectiveness are probably much bigger and much more expensive than ferros.

A constant voltage transformer (CVT), also known as ferroresonant or "ferro" transformer, is arranged so that part of its magnetic path is in resonance with the main frequency. The resonant part is about 1/3 to 1/2 of the iron and copper, and there's a big (generally oval) metal cased polypropylene film capacitor for the other part of the resonance. This is one big, mean, deep, filter. Hash on the power line in general has a very tough time getting in.

The resonant circuit is the electrical analog to a flywheel. The stored energy resists being pumped up and pays out energy when it's shorted from the mains.

On top of that it *regulates* the output AC in a meaningful sense, not just "how far down does it droop" like other transformers call regulation. We used to have ferros that put out +/-5% outputs with AC inputs from 85 to 132Vac.


Ebay has become not nearly the great deal it started off as, but you can generally find CVTs there for about $50-$200 in the 500VA range that would comfortably run a guitar amp in most cases. Then there's shipping...

[Daver]

OK, more info. I used a variac and dropped the incoming voltage to 115VAC. That changed nothing. I, again, changed guitars, cords and amps. Even my Fuchs ODS when clean exhibits the "noise" and that's pretty heavily filtered. I hooked up my scope to the AC line. I got a fairly decent sine wave with slightly flat tops. The sides aren't completely straight but there's no notches. The tops have a little bit of a point on the edge before the waveform goes down, or up. I don't see any hash or other traces along with it. So does this mean my power is OK? I've moved my amps around the room thinking maybe something was vibrating but it always follows the amp and the volume doesn't have to high to hear the noise. It almost sounds like a bad or loose speaker but all my speakers do it. Any ideas? Thanks.
Dave

[Steve Conner]

I've never seen a line voltage waveform that didn't have the flat tops. I don't think they are an issue.

Is it possible that all your gear always did this and you only just noticed?

Is something mechanically vibrating in the room? I once spent ages tracking down a rattle in a combo amp that turned out to be coming from the central heating radiator on the other side of the room. Try moving the amp to a different room.

I guess what I'm saying is, I can't see how poor power quality would cause one very specific distortion artifact. It's more likely to just make the amp as noisy as hell at idle.

Those constant voltage transformers recommended by RG are great for stopping your trailer blowing away in a hurricane. They're much less common nowadays as more and more equipment uses regulated power supplies.

[Daver]

Steve,
I don't think this has always been an issue. I've lived here a long time and I've never noticed this. It's pretty evident. I moved one of the amps to another room and it still has this noise. I tried playing in the dark in both rooms just for the heck of it and that didn't change anything. It always seems to be coming from the speaker and not elsewhere in the room. I can turn down the volume pretty far and still hear it. I brought home a transformer isolated line filter for a copier from work to try. Not that that's the best thing to use but I figured I'd give it a go. No change. I suppose the variac provided some isolation as well before. This is just killing me. If it's not the power, I can't think of anything that would cause this in all amps, with all speakers, cables, guitars, etc. and in different rooms. What else can I test? I'll be able to play at a different house this weekend, but I'd sure like to get this sorted out now. Thanks.

[Enzo]

But playing at another house is one of the best tests you can do for something like this. It will either tell you the environment is at fault, is whatever way it occurs, OR you will find that sure enough, there is something about the amp itself.

Isolate the problem.