AC Line Filter and/or Regulator....What do you use?

[ajm]

12-14-2025

I looked at the forums and hope I have this posted in the best spot.
I did a brief search as well and didn't see anything.

I have all the makings of a bad stew.
An old house with old wiring, assume all outlets ungrounded.
Half a block from several buildings with God knows what antennas on their roofs.
Half a mile from a major international airport.

Details:
I have grounded the house AC outlet that I'm using to a water pipe. AFAIK all of the other outlets in the house are ungrounded.
I have a Furman PL8 rack mounted type power strip plugged into the outlet.
I run my amp and effects (none digital) off of the Furman.
Using a Kill A Watt AC current meter I'm drawing less than 2 AAC total.

Over the past year or so I am getting strange noises coming through the amp.
It's hard to describe but it's sort of a bleeping type sound if that makes any sense.
No CB radio voices.
I have tried several things to try and isolate the problem.
I have even unplugged the guitar and the effects from the amp, and it still comes through the amp alone.
The more overdrive there is the more it comes through.
I have tried other amps, same thing.
I have a wall wart powered old answering machine in another room, and occasionally it comes through faintly on phone messages.

I'm not sure if it's the AC service, or if it's an over the air thing.
I have a feeling it's the service.
I don't know if any of the neighbors have issues, but none of them play guitar.

I have a friend with a battery powered generator that I can borrow.
That is on the to-do list.
In less than a minute I'll probably know if it's an AC service issue, or an over the air issue.

So...........

Does anybody else have a similar problem?
What has been the solution?
An AC filter better than the Furman?
An AC regulator?
Any part numbers?
If it's a service issue, call the electric company?

Thanks in advance.

Search terms:
AC
Line
Regulator
Supply

[Larry Dering]

Are you laying your cell phone anywhere near the amp? Try turning cell phone off and see if it happens. Turn the amp at different angles and listen.

[Dave Grafe]

Are you laying your cell phone anywhere near the amp? Try turning cell phone off and see if it happens. Turn the amp at different angles and listen.

Definitely sounds like cell phone interference, a phone can induce noise in a pickup or electronics circuit if it's close enough. If the noise was in the electrical service your Furman would catch it.

If you have a ham radio operator broadcasting nearby it is conceivable that airborne interference could affect your pickups but not likely the amp by itself. Go talk to your antenna-laden neighbors. If they are not transmtting RF your problem lies elsewhere.

[ajm]

Cell phone nearby (in the house)?
Nope.

HAM transmitting neighbors?
That could be tough to nail down.
Besides, I don't get voices coming through.

Computer nearby?
Nope.

The noise/interference that I'm getting is tough to describe.

[Dave Grafe]

Okay we have ruled out the cell phone but not ham radio interference as sideband interference is the most common kind.

https://electronics.stackexchange.com/q ... y-problems

If you experienced the same issue with other amps and speakers the amp is ruled out. If your second amp used the same speaker for the test the speaker is NOT ruled out. Nearer to home "chirps" can happen with bad patch cables, speaker cables, voice coils, really anything that intermittantly shorts or opens the electron flow.

Keep us posted

[Bob Sykes]

Interesting problem. Seems obvious but worth saying that all EMI problems have 3 elements. Source, Coupling mechanism(s), and victim. The victim is the only known here. It appears the evil cell phone bleeps have been eliminated.

Sounds a lot like my old house (including proximity to the airport). I also have some outlets grounded to the copper water pipes. These pipes should be bonded to the ground rod, probably near the meter/service entrance. My water piping has a solid plastic feed pipe before it goes into the ground, making it electrically "floating" without that bonding wire.

Everything you have done so far are good steps to isolate the problem. I'm sure you know overdrive will boost the audio noise floor. Are these tube amps or solid state? Tube amps are usually more susceptible to radiated RF noise.

The interference (also) on the telco line points to radiated noise coupling into your house. This landline should also be grounded at the service entrance.

Could be both radiated noise coupling into the AC wiring and/or directly illuminating the amps. House wiring makes an excellent longwire antenna. It may just be your service or could be the neighbors don't have anything with vacuum tubes

The generator should be helpful if its output waveform is "clean" (Nice 60Hz sine wave). This doesn't sound like an AC regulation problem.

You can try calling the power company. They intentionally inject RF signals into the grid for various purposes.

There are always better filters available but I'd hold off on the spend until the noise source and/or coupling mechanism(s) are better understood. Does the noise get louder if you bypass the Furman? A RF spectrum analyzer would tell the story if you can get your hands on one. Is the noise constant or intermittent? The generator would eliminate the power company question. If that doesn't work, my SWAG is airport telemetry. Airports (and planes) can radiate significant RF fields as data transmissions as well as voice communications. You'll have to wrap your house in tin foil to fix this

HAM radio operators also can transmit data, so the lack of voice modulation doesn't completely rule them out. Most HAMs are fairly knowledgeable about electronics and interested in resolving interference issues that their equipment is causing. They are however under no legal obligation to do so in this case. IF the interference is affecting "over the air" T.V. or radio reception, you could complain to the FCC. Guitar amps don't get any protection from them so it's back to the tin foil shielding unfortunately.

As Dave said, keep us posted.

[Dave Grafe]

Occasional loud "chirps" are most likely a bad connector on the amp's speaker cable, especially if it's plastic molded one.

[Tim Rose]

My electric company sends a 12.5khz ping to read the meter.. so they say. Happens every 30 sec of so.....can hear thrrough poorly wired systems....drives me nuts

[Lee Baucum]

My electric company sends a 12.5khz ping to read the meter.. so they say. Happens every 30 sec of so.....can hear thrrough poorly wired systems....drives me nuts

Gone are the days (for many municipalities) of the "meter readers" walking around reading meters. (I used to be one!)

The meter readers have been replaced with "smart meters". Electric meters and water meters. Don't know about gas meters.

~Lee

[ajm]

Update 12-18-2025.

I suspected that the issue was coming from either:
- Over the air radiated RF junk, or
- Through the AC power lines.

I have a friend that has a portable battery powered AC converter/generator.
I suspected that this is an AC power issue.
Yesterday while waiting to use the generator, I decided to cross one possibility off of the list.
My music room is on the north side of the house.
I took an amp to the south side and hooked it up.
None of the noise/blips/fluttering/etc issues!!!!!!!!!!!!!!!

I took the amp back to the music room on the north side.
The problem was still there.
Assuming it's not an AC power issue any longer, I started messing around.
Picking up the amp (a small combo) and rotating it and moving it around the room made the problem come and go.
Then...........
I sat the amp in its normal spot and noticed by accident that walking between the amp and a north facing window made the problem come and go.
So, what's directly to the north?
Gee, not much. Only:
- A 5 story hotel, with what looks to be some kind of antennas hanging off the side, about 100-200 yards away.
- To the west of the hotel, about another 100-200 yards, what can best be described as a "tree" looking tower with all kinds of antenna looking stuff on it.
- To the north of the hotel, across the street, a major international airport.

Just to be thorough, today we tried setting the amp up to pick up the noises.
When connected to the house AC the problem was still there.
Then we tried using the generator to isolate the amp from the house AC.
The problem was still there when using the generator.
I'm going to conclude that the problem is NOT with the house AC wiring.

So for grins, I got a couple of rolls of tin foil.
I started running strips of foil covering up the window.
By the time I got the whole window covered this problem is basically completely gone.
Note that the foil is taped over the window to the wall and is NOT grounded.

Now for the next step.
Some options are:
1) Leave the foil covering up the window.
It seems to work, but it's nice looking out the window when practicing.
2) The window has an outside screen.
Right now it's nylon or whatever.
So, try replacing the screen with metallic (Home Depot has aluminum screen material).
Then get rid of the foil.
I won't know if it works until I try it.
Thoughts?
Will the RF still get through the screen?
Would it be helpful to put 2 layers of screen up, one over the other, for better coverage?
Would I need to ground the screen? (Note that the foil is not grounded).
3) Any other (legal) ideas? ;>))

Thanks in advance to all who have chimed in.

[Bob Sykes]

Sounds like you have figured it out. Copper/bronze screen will work best if you can find it. Not cheap. It's used in some commercial Faraday cage constructions. The screen does not need to be grounded. 2 layers of screen works better but they need to be electrically isolated from each other.

Sounds like the interference is over 1GHz. Once you get into that region, the signal become more "line of sight" and can be attenuated with free-floating barriers (your foil) in the window. I'd look into increasing the shielding in the amp. What kind is it?

I find that wearing a KFC bucket covered with foil on my head clears things right up (for the unfamiliar - google Buckethead)

[ajm]

Bob Sykes: Thanks for the reply and suggestions.
Questions, etc..............

"I'd look into increasing the shielding in the amp. What kind is it?"
There are several different amps, all combos.
A couple of them have an aluminum plate stapled under the top like the old Fenders.

"2 layers of screen works better but they need to be electrically isolated from each other."
I'm not sure that I understand.
I thought about replacing the plastic/fiberglass/whatever is on there now screen with some aluminum conductive screen.
When I do it, I was thinking of putting one layer on top of the other.
Are you saying that this is not ideal?
Note that what I currently have is aluminum foil taped up across the window.
In reality, isn't aluminum foil the same thing as screen but without the holes/gaps?

I also have been thinking of doing the screen on the outside of the window, and then making another screen assembly for the inside of the window as well.

Thanks in advance.

[Bob Sykes]

One layer of aluminum screen will work as well as the foil IF the holes in the screen are relatively small in relation to the wavelength of the RFI. Higher frequency = shorter wavelength. A common practical example is the window on your microwave oven. The mesh size in that window is just small enough to block the 2.4GHz R.F. energy inside. It would not work as well at 3 GHz. I'd suggest trying aluminum screen and see how it works as the wavelength of the RFI is unknown in this case.

Two layers of screen on top of each other will act like one screen. It will reduce the hole (aperture) size if not perfectly aligned and therefore work at higher frequencies. It will not increase the shielding effectiveness [S.E.] (in dB) if the hole(s) are already small enough. This is where two electrically isolated layers work better than one.

Some commercial shielding panels are constructed using a frame of 2X2 wooden sticks with screen stapled to both sides, but not touching (connected).

Hardening the shielding on the amps would require some science experiments to determine the vulnerable section(s) of the circuit and the RFI ingress path. I'm assuming the pre-amp/inverter tubes do have the metal cans over them already?

[Dave Grafe]

Kudos on the scientific analysis technique

[ajm]

Update Monday 12-22-2025
The science project is ongoing, but...........

I bought some aluminum screen material and parts for a frame at Home Depot.
I replaced the polyester/nylon/fiberglass/non-metallic existing screen with aluminum.
Installed the new screen on the outside.
Note that the screen nor the foil are connected nor are they grounded at this point.

Checked the noise problem inside with the foil still hanging.
Didn't seem to matter, the problem is still basically gone, except one amp in the room probably because of its position seems to have a little bit that had either crept in or that I didn't notice before.
Then.............
I started removing the foil strip by strip. It was installed in horizontal strips across the window on the inside.
I checked the problem after each strip was removed, and by the time all of them were removed the problem was still gone with 2 of 3 amps in the room.
However, if I'm being picky there is still a little bit of problem waaaaay down at the bottom in the noise. You'd never hear it when playing in a band or with another instrument. Like I said, being picky. It is MUCH better than it was.

Next steps:
1) There are a couple of other screens/windows that are not really line of sight. They may get the aluminum treatment.
2) Hang a screen up on the inside or the room over the main offending window.
That would be easy, I can temporarily tack/tape it up.
It would be maybe 1-2 inches separated from the outside screen and electrically isolated.
The chances of the holes lining up with the outside screen are basically 0%. If that ever happened, we had all better buy a Powerball ticket. ;>))

I forgot to add the amps. All using a grounded AC outlet.
- A 1984 or so Carvin XV112E.
Foil sheet stapled inside above the chassis like the old Fenders.
One shield over the first preamp tube socket.
The one with the problem waaaay down in the noise floor.
- A Peavey Studio Pro 50 (the one that still has a little of the problem coming through, slightly more than the Carvin).
No tubes, solid state.
Foil sheet stapled inside above the chassis like the old Fenders.
If I move this one to the back of the house it is dead quiet.
- A Marshall solid state combo MG30FX.
Because of where it's sitting, I'd think that this one would be the worst offender, but no problem whatsoever.

Once again, thanks for the help.
I'll keep you posted.

[Dave Grafe]

Excellent progress report!

[ajm]

By the way, FWIW and for your entertainment...............

It seems as though this problem does occur from time to time.
At some point the other night, while eating dinner and watching Youtube videos, this one kept getting suggested to me.
Probably cause I'm a Van Halen/EVH fan.
I wasn't going to watch it since I figured that I've heard all of the stories before.
But what the heck, I clicked on it.
It had time stamps so I browsed them to minimize time wasted.

Lo and behold there was one that seemed appropriate.
Go to 12:37 for about a minute or so.
Like I said, FWIW, YMMV, etc etc etc.

https://www.youtube.com/watch?v=arohd5umLgc

There is a link in the YT info to an article.
Lots of tech stuff on construction and wiring.
Concerning the "chicken coop" shielding:

One unique problem confronting us was KMPC, a 50,000 watt AM radio station sited just three miles from 5150. It was also a necessity that Ed be able to play in any location facing any direction, without hum, RF, or noise problems. Our solution was to build a chicken coop (grounded, of course): standard chicken wire was used in the walls, flooring, and ceiling to surround the entire recording area. The wire enclosure was tied to our central ground, and at no point touched any electrical conduits. The concept worked flawlessly.

[Dave Grafe]

https://en.wikipedia.org/wiki/Faraday_cage

This is how casinos and secure sites disable cell phones

[Bob Sykes]

Great progress and evaluation methodology. You have certainly lowered the noise floor. Keep in mind there may be more than one coupling mechanism so if you eliminated the radiated noise 100%, you might hear some residual low level noise coupling in through the power lines. The portable generator and line filter would be useful again for those experiments. Notwithstanding all of the above, at some point you will have plug in guitars and cables etc. introducing other noise ingress paths.

A small clarification on the screen shielding;

-Two layers of (misaligned) screen laying on top of each other will reduce the aperture size and shielding effectiveness at frequencies higher than one screen layer. It won't increase the shielding effectiveness at the frequencies already attenuated well by a single layer.

-Two layers of (misaligned) screen separated by an inch or two will increase the shielding effectiveness at the same frequency range as a single layer. It won't decrease the effective aperture size (and upper frequency) much.

The Faraday cage pictured in the Wiki link that Dave posted shows a typical construction with two layers of copper screen supported by a wooden frame (aka double shield construction). The "screen within a screen" is only connected together at a single point. These rooms work well below microwave frequencies. They are relatively cheap to build, provide great visibility inside and they keep the bugs out At higher frequencies, solid metal panels are needed which are either welded or clamped together. Disadvantages are you can't see through the solid walls and climate control may be needed if the equipment inside generates much heat.

The "chicken wire in the walls" recording studio shielding works well at AM radio frequencies. Shielding is all about wavelength. The wavelength at 1 MHz (middle of the AM radio band) is between 2 and 3 football fields in length. Whereas above 1 GHz, wavelength is expressed in inches or centimeters.

I used to demonstrate this by playing a battery operated AM radio standing outside of a Faraday cage. I would then step inside of the cage, leaving the door open and the radio would cease to play the AM station, only static remained. The 8' X 4' wide door opening in the cage is "small" with respect to AM radio signals.

A common misconception is that Faraday cages must be grounded to work. They work just as well "floating". The reason(s) for grounding them is Safety (shock prevention) just like any other metal enclosure and to prevent electrostatic charge build up.

Probably more than you wanted to know, but I used to live, breath and eat this stuff in a previous life Now I only dabble in it.