Why Your Preamp Hums and How to Fix It

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Preamp Hums

The excitement of unboxing your new entertainment gear cannot be put into words.

As you wire, mount, and hook everything up, you can’t wait until you can turn up the volume on your favorite Star Wars scene. This is going to be the best thing since sliced cake! Going to the movies is going to be old news.

Instead of crisp sounds coming from every corner of the room, you hear chatter, buzz, and a gentle hum coming from the preamp. Except the sound is not gentle. It is loud and irritating! What to do? What could it be? Firstly, let’s take a deep breath and relax.

Usually, the hum emanates from your speakers and caused by a ground loop. This is the most common reason for the humming noise, and fortunately, the easiest to solve.

Another reason for the humming noise emanating from your speaker could be your transformer, bad wiring, or defective equipment.

Fortunately for you, audio and video systems are rarely quiet on initial set up. Having a humming noise is completely normal. Let’s prepare to dive in and take a look at the reasons for the humming noise, and what we can do to eradicate them.

What Is That Humming Noise?

At one point or another, especially when first setting up your home theater multimedia system, you will experience audio noise emitting from either your speakers or your equipment.

Hums and buzzing noises come in two distinct flavors. Sometimes they are obvious, and sometimes they are not. The not so obvious humming flavor is a non-irritating drone, usually in the range of 50 to 60 HZ.

The obvious flavor of the higher-pitched hum usually ranges from 100 to 120 HZ. Trust us when we say you will know it is the higher-pitched sound.

What Could It Be?

At this point, it is crystal clear that the sound of your much-coveted entertainment gear isn’t so crystal clear.

We would love to say you have done nothing wrong, but then again you may have. Inadvertently of course. There is also the possibility of bad wiring, defective equipment, or even caused by a noisy electronic environment.

Sometimes, you will get video hum as well, usually seen as diagonal bars coming down the screen of your TV or projector.

So what is the cause?

The answer could be one of several things: AC line noise, faulty wiring, or a ground loop. So how do we determine which? And after we determine the source, what are the steps we can take to eliminate the noise?

Before we can answer how to get rid of the noise, let’s further examine the two distinct noises, as the sound level will be our first indicator:

  • A 60 Hz humming noise will be caused by equipment in close proximity to other equipment or caused by cable or wiring problems.
  • A 120 Hz humming noise will be caused by ground loops.

Let’s explore AC line noises, faulty wiring, and ground loops individually.

Ground Loops

Ground loops are the number one culprit of the humming mystery as they are so easy to create.

Often, when ground loops are the culprit, a loud humming noise or buzz emits from the speaker system. Pesky and weird scrolling bands will also manifest on your TV screen when ground loops are to blame.

How Do Ground Loops Occur?

A ground loop typically occurs in an entertainment system when one or more pieces of equipment are plugged into the same alternating current at different locations. These components are then connected by an electrical signal cable versus an optical signal cable. These electrical signal cables can be RCA cables or HDMI cables, whose shielding is connected to ground.

What the heck does this mean? Glad you asked. In layman’s terms, this creates a single-loop antenna. This single-loop antenna then, via electromagnetic induction, draws in various types of noise. Don’t you just love that?

Here is a diagram to further help process this phenomenon:

How Do I Get Rid of It?

When it comes to ground loops, the easiest way to get rid of the humming noise is to simply power everything via a single AC socket. This can be achieved by using a single power strip or surge protector that plugs into the wall. Et voila, problem solved.

On average, most entertainment and multimedia setups can be powered effectively via a 10-amp circuit (which most household circuits accommodate).

What If I Can’t Accommodate a Single Socket?

There may arise cases where you simply can’t accommodate a single AC socket for your multimedia equipment. This often occurs with self-powered speakers and subwoofers.

In these dire scenarios, you can opt to buy a hum eliminator, which will roughly run about $80. The idea is to interrupt the ground loop in the signal cables.

What If the Humming Persists?

If these methods do not yield the results we are looking for, we may be facing OAT (over the air) antenna that has its own path to ground. We may also be looking at any cable TV or coax cable that has found its own path to ground.

Due to the insulation found in cable modems, cable boxes, or the like, normally this scenario is only likely to occur if you are connecting a wire directly to a TV or a video recorder.

After investigating, if you have traced the root issue to a TV signal wire that’s attached to a modem or cable box, simply disconnect it and reattach. If the problem persists, look into replacing that piece of equipment, as it is most likely faulty.

How to Troubleshoot Ground Loops

Once you have identified that the humming noise you are experiencing is a ground loop issue, the process of elimination to pinpoint the source of the ground loop starts. It is essential to determine where the humming noise is originating from, in order to effectively cure it.

Ground Loops in Audio

  • The first suspect in an audio humming noise situation would be the power amp or the receiver driving the loudspeaker.
  • To troubleshoot, first, turn them both off, disconnect all inputs from them, then turn them back on.
  • If the humming problem is still there, then the problem lies with the receiver or the power amp. From here, checking with the manufacturer and dealing with an exchange is the way to go.

Ground Loops in Video

  • For a video situation, inspect sources like DVD players, rather than cable or satellite.
  • First, always assume it is a connection or cable problem. Poorly shielded cables are usually the culprit of humming noises, above any other kind of problem.

AC Line Noise

Unfortunately, ground loops are not the only culprit of electrical noise. The downside is that any device with a motor, such as blenders and hair dryers, will create this type of interference.

As with ground loops, AC Line noise may be audible through your audio equipment or visible on your TV screen, or the sad news, it may not.

The cure to this type of interference, and perhaps the most obvious response, would be to not use these types of equipment while binge watching Netflix or Hulu. For example, refrain from blow-drying your hair while Friends marathon is running in the background.

This may work if you live alone. However, if you live with family or roommates, perhaps not. If this is the case, we have just the thing for you.

What Should I Do About AC Line Noise Interference?

If you cohabitate with others, there are a couple of viable options for you. Investing in an online UPS, or interruptible power supply may be the way to go. You can also choose to invest in an isolation transformer.

Online UPS

ups

An online UPS unit works by having a backup battery always engaged, hence the name online, between the input AC current and the output AC. The electrical power goes through a conversion to DC (direct current), and then back to AC. This process will, in turn, remove the noise. This is known as dual conversion.

A true online UPS unit runs a bit on the expensive side. Price tags can vary from an average $100 to $700 (yikes), but well worth it.

Some online UPS units are the size of small dehumidifiers and include features such as USB monitoring. This is helpful in the event of power failure, as it will gracefully shut down attached electrical equipment. These units also provide protection against power surges and outages.

A good online UPS unit that advertises sine-wave output is a good starting choice for anyone looking to reduce electrical interference. This should run an average of $100.

Isolation Transformer

Isolation transformers are slightly cheaper than an online UPS unit but very effective against all kinds of line noise.

Prices, usually depending on wattage range from $200 to $500 for higher-end models.

An isolation transformer, in a nutshell, works by employing a shielded transformer that turns dirty AC into clean AC. This is done via electromagnetic induction.

What Are the Uses of the Isolation Transformer?

Isolation transformers are designed for use with delicate diagnostic equipment in mind, where even the most minimal of AC noise can cause spurious readings. Since this is the case, isolation transformers are that much more substantial when used for an in-home multimedia setup.

Multimedia Setup Wiring

When it comes to your multimedia wiring, there are a few hard rules to always oblige by:

Rule Number One

Never run a power cable across or near any audio or video wiring or cables. This includes antenna wiring.

Signal cables of today are constructed to be well shielded; however, if you are receiving the dreaded humming noise and it is not a ground loop, the wiring could be to blame.

If you have self-powered speakers, note that cables running into the speakers are audio signal cables (not output cables).

Take note that any three-wired balanced signal cables are less susceptible to humming noises as a result of a nearby power cable, than a two-wired cable. Consequently, if your equipment provides you with the option of using balanced outputs or inputs (three-wired cables), then do so.

Rule Number Two

Another rule that we will want to keep in mind and be on the lookout for is not looping antenna signal (twin-lead) cables. In doing so, will lead to the same noise. This occurs because looping twin-lead cables cause them to become antennas themselves via electromagnetic induction.

Cables fabricated poorly can also lead to noise interference issues. However, there is still not any significant advantage in purchasing a pricey cable.

A common misconception is that the more expensive the metal, the better the cable. This is not correct. For example, gold is used on connectors because of its non-oxidizing properties, and not because it is the best for electrical conductivity.

Gold is quite good, better than nickel and chrome, however worse than silver and copper.

Although very rare, one thing to look for in cabling is to ensure that the cable isn’t microphonic. Physical shocks can be turned into audible signals. This is mostly for Hi-Z applications, such as guitar cables and such, however, it is worth a mention!

RF Interference

If you have ever paid attention to the construction of your stereo receiver, the inner walls are always made of metal. Ever wonder why?

While almost everything else in the manufacturing world is made of plastic, there is a reason for receivers and other electronic devices have metal walls.

Fun fact: metal walls in receivers and other electrical devices are meant to block incoming or outgoing RFI, or radio frequency interference. Conductive materials tend to block RF signals by stopping and sending RF signals to their surface.

RF interference is everywhere these days. RF interferences are emitted from every device imaginable: cell phones, laptops, any smart devices, anything that connects to Wi-Fi, and the Wi-Fi equipment itself.

With so much emitting RF signals, the next viable option is to lessen the strength of the signals that interfere with your multimedia equipment.

This can be achieved by keeping all RF-emitting equipment away from your home theater equipment as you can.

If it is a device that has to be near your setup, ensure it is properly insulated, so as to reduce RF signal emission. 

USB/HDMI Cable Noise

There are several methods in removing USB and HDMI cable noise:

  • One method is to use a cable with a ferrite noise suppressor sleeve. It looks like a big round slug at one end of the cable. Here is an image of a cable with a ferrite noise suppressor sleeve, so that you have a better idea, you’ve seen them before!
  • Similarly, you can also opt to purchase a clip-on ferrite noise suppressor.
  • The second method is to run a wire that is less resistive than the USB or HDMI cord that is hooked up to your audio component. A speaker wire would be okay. The idea here is that electricity always follows the path of least resistance, so current would run down the ground wire rather than your USB or HDMI cable’s shield. Clever huh? This is called a shunt.
  • The third method is to purchase a USB noise filter. The average costs of these are around $50.

Mechanical Hum

If it is a mechanically induced hum, the noise will be coming from one of your equipment components rather than the speaker system. The causes for this could be poorly designed power transformers.

More often than not, a mechanical hum is caused by the transformer.

Why Do Transformers Hum?

So why do transformers hum? The short and sweet answer for this is that transformers hum due to an effect knows as “lamination rattle.” This is caused by DC voltage on the line. This can also be due to poor construction, and sometimes both.

Troubleshooting

As you can see, a huge part of solving the problem is troubleshooting various scenarios until dwindling down, by process of elimination, to the correct scenario.

Fortunately for us, the problems are always the same and well known. There are differences between troubleshooting video issues, and troubleshooting audio issues, so figure out which of the two is step one.

Taking preventative measures and keeping in mind multimedia wiring set up 101s, such as described above, will help you from having ground loops issues and prevent the dreaded humming noise.

Remember, finding the problem is nine-tenths of the work in finding the solution. Navigating through the jungle of multimedia wiring and cables can be daunting, but do-able!

I Can’t Hear It Anymore!

Using the above methodologies and guidelines should help you to troubleshoot the humming noise mystery of your multimedia setup.

After you’ve identified the humming noise culprit, by implementing our suggestions, you should be able to eliminate all noise that is not inherent to your audio system!

Now that you’ve got everything squared away, it is time to kick back and enjoy the show (or the sound)!