Understanding Hum Elimination

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Back in 2022, and early 2023, I built 6 different circuits designed to eliminate hum and noise relating to guitars and amplifiers. Even thought I had solved the age old issue of noise in single coil pickups. I got busy with other projects and totally dropped my extensive work on hum and noise circuits. Before I stopped working on the noise and hum circuits, I did learn that none my circuits solved noise in single coil pickups.
Last night I was practicing on my pedal steel, and my amplifier had a pretty loud hum. I was so interested in what I was trying to play my mind had tuned out the hum. Finally after a couple hours of torture Joy came to me complaining about the loud hum. I knew my steel guitar had a humbucking pickup. I suspected the source of the hum was the real old Peavey amp I was using. If the source of the hum was the real old amp, I figured the only solution was to change amps, or fix the old amp.
Then I remembered the 6 hum and noise circuits I had built, that were laying on a shelf in my parts room. The first one I hooked up failed to even conduct a signal. I went and got a second circuit, plugged it in, and was totally blown away. There was zero noise coming from the 50 year old Peavey Session 400 amp. Correct me if I am wrong---Amp made in 1974, now it is 2024---that is 50 years!
That got me to thinking. I went back and read all the posts I made on the Steel Guitar Forum concerning the 6 circuits. Then I started looking at the circuit that solved my big hum problem.
Here is the basics of the electronic design that worked so great: I combined two different proven ways of eliminating noise and hum. A op-amp driven transformer, and circuit that provides differential signaling. Both methods are used in telecommunication electronics. My 50 year old amp was dead quite, and there was no frequency loss as there is in suppressors and noise gates.
I wondered if I could produce and sell copies of this design. Most of the noise and hum devices on the market claim to cure all problems, even cancer and bad breath. There is no hum and noise device on the market that will cure all problems. A few of the sources of noise and hum are: Single coil pickups, Ground Loops, defective equipment, defective connecting cords, magnetic interference, and radio frequency interference to name some of the main contributors of noise and hum.
If you have humbucking pickups, the single biggest source of hum is ground loop noise. I think my circuit solves that problem. I also think my circuit solves most of the RFI noise through radio frequency limiting capacitors. I could not truthfully say that my circuit solves all noise and hum problems. Read the sales pitch of the Hum Busters for sale on sites such as Amazon, eBay, Reverb, Musicians Friend, and Sweet Water. From the advertised description of these hum and noise devices one would think they would cure a tooth ache, or even a ingrown toe nail.
I think I am going to produce and market this circuit that worked so great for me. I may not sell very many, but I am going to be honest. I am going to list what the circuit eliminates and what it will not eliminate.
I am certain the circuit could save some recording sessions, and important gigs for musicians with ground loop hum. Is it better than other similar products? All I know is what I have built. It has two proven methods of eliminating noise and hum, with RFI suppression. The circuit does not compromise tone--create frequency loss.

Roger Crawford · From: Griffin, GA USA

Keith, would this circuit eliminate white noise from amps when the gain is high?

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Roger, I will try to answer that question. First, let me say all noise, even white noise has a source. It comes from somewhere. You could unplug the guitar cord, then the source would be the amplifier. If a guitar cord is plugged into the amplifier, then the source of the white noise could be one of the things mentioned.
I am going to answer your question by saying it is possible the circuit could eliminate white noise. It is also possible the circuit would not eliminate white noise. It all depends on the source of the noise.
To understand what I am getting at, I need to give a brief explanation of a transformer, and differential signaling in hum and noise reduction. The beauty of a transformer in noise and hum elimination is two fold. It separates the source of the signal coming in to the amplifier from the the amplifier. It also separates the signal ground from the amplifier ground, which is so important in getting rid of ground loops. Most people understand the operation and benefits of a transformer in isolating noise and hum. The trick to using transformers is to design the circuit to not loose frequency--tone! Not everyone understands differential signaling. To understand, differential signaling, look at a XLR cable. There are two signal connections, and a ground. The two sine wave signals carried on the XLR cable are totally separate, and 180 degrees out of phase. When the XLR cable reaches it's destination only the difference in the two out of phase signals is amplified. What is common to both 180 degree out of phase signals is not amplified. Well guess what---Noise or hum can be common to both 180 degree out of signals. I just said--"ONLY THE DIFFERENCE IN THE TWO SIGNALS IS AMPLIFIED!" Noise common to both signals----"IS NOT AMPLIFIED". In the final termination the two sine waves are transformed into one sine wave with a ground. Meaning you have a 1/4 inch guitar jack, where you can plug in your guitar cord going to your amp.
There is nothing new about what I am doing, the telephone people have been doing the same thing for years.
Roger, getting back to your question; Yes, it could eliminate white noise, or might not eliminate white noise. It all depends on the source of the noise or hum. I can relate this information from my own recent experience. That old 50 year old Peavey amp I told you about in my post above had ZERO white noise. That might not be the situation in every case.
99.9999% of noise and hum elimination products are made in China. So who are you going to trust, an ad on Amazon, eBay, the knowledge of a kid selling stuff on Sweetwater or Reverb?

Jeff Highland · From: New South Wales, Australia

Surely the first step in eliminating Ground loop hum is to eliminate ground loops by ensuring a common ground?

The worst noise issue I have had in my studio was when using a pedalboard with headphones and with dc power (so no Ground connection) I had to either plug into a grounded amp or provide a direct link to mains ground.

But then in Australia we have exclusively had 3 prong grounded outlets for as long as I can recall
_________________
Duesenberg Fairytale
1949 Supro Supreme
1950 National New Yorker
2008 Highland Baritone Weissenborn
2020 Highland New Yorker.
2020 Highland Mohan Veena
2021 Highland Weissencone

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Jeff, insuring a common ground does not always guarantee elimination of ground loop noise. All DC power has a ground of some type or it would not work. Grounds are sometimes difficult to determine, besides a DC or AC grounds you have an audio ground, which can be different.

Jeff Highland · From: New South Wales, Australia

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Jeff, yes I agree, having a common ground is a great first step.

"What about a battery? dc plus and minus but no earth, and a 2pin ac to dc pedalboard power supply is just plus and minus no real earth connection"
Jeff, everything in electronics boils down to two simple things, Voltage and Current. Electronic devices can work without having a earth ground. Most of the time, but not always, 2 pin AC is converted to DC, for use on a circuit board. DC voltage and current is no different if it comes from a battery, or is converted from a 2 pin AC power supply. The import thing to consider is the ground, because it can mean more than one thing. A particular ground can even determine voltage polarity. A 2 pin AC to DC pedalboard power supply, nowadays, means a switching power supply was used. In the old days transformers were used. A rectifier is used to convert the AC to DC.
As far as the noise in your studio, I would have to know a lot more details before I could understand why you needed a earth ground.

Jeff Highland · From: New South Wales, Australia

We are plugging in devices like guitars with an unbalanced cable with "hot" conductor and shield.
All the metal elements in the guitar like strings, bridge, shielding etc are "grounded" by connecting them to the shield of the cable.
My experience was that if using equipment like a pedalboard to headphones without a connection to mains earth through a grounded amplifier, the metal parts of the guitar acted as an antenae. Easily solved by providing a link to mains earth or plugging in to an amplifier (turned off)
_________________
Duesenberg Fairytale
1949 Supro Supreme
1950 National New Yorker
2008 Highland Baritone Weissenborn
2020 Highland New Yorker.
2020 Highland Mohan Veena
2021 Highland Weissencone

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Yes, Jeff, unbalanced cable guitar connection, I agree. I have seen guys using battery powered effect pedals, and a battery powered amplifier. Nothing connected to a earth ground. First off, is your guitar pickup, or pickups, single coil or humbucking? Single coil pickups make the strings of a guitar act like an antennae. A ground loop can also make the grounded parts of a guitar act like an antennae. It sounds to me like you have a ground loop. If the circuit I built was battery powered, and you plugged it between the headphone speakers, and the rest of the gear, I am guessing it would break the ground loop. Seems to me the problem is a grounding problem, with something creating a ground loop. Only experimenting would find the grounding problem.
From your description, pedal board is battery powered. You have not said what is powering your headphones. Something has to be powering your headphones. Headphones don't work without something powering them.

Jeff Highland · From: New South Wales, Australia

Actually the worst was my Duesenberg with Humbuckers But with a lot of metal connected to "ground"
Headphones were plugged into a headphone output on a pedalboard device, so no connection to mains earth.
Anyhow this was a few years ago I resolved the problem.
_________________
Duesenberg Fairytale
1949 Supro Supreme
1950 National New Yorker
2008 Highland Baritone Weissenborn
2020 Highland New Yorker.
2020 Highland Mohan Veena
2021 Highland Weissencone

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