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  Finding and Fixing HumVery few audio or video systems are dead quiet. There are usually always a few hum related problems. If your system has a bit of hum, is it the transformer or not? How do you determine the source of hum and what can you do about it?Sometimes hums and buzzes are quite obvious, sometimes not. The 'hum noise' usually comes in two flavors, a low non-irritating drone (50 or 60 Hz) or a slightly higher pitched buzz or raspy/irritating 'angry insect' sound (100 or 120 Hz). Video hum is usually seen as diagonal bars across the TV or screen of a projector. Every audio/video system has some degree of either audible or visual hum or buzz. If your system has some of these noises, and they are at a level that is noticeable or bothersome to you, there are a few things you can do to fix these problems. Find out what's making the noise We first need to divide our search into two categories; electrically or mechanically induced hum. To see if it is an electrical problem, make sure your system has been on and warmed up for at least 10 minutes, then simply place your ear near the loudspeaker (with no music playing) and listen to determine if the hum or buzz is coming from your speaker. If it is, then at least one component of your problem is electrical. A mechanically induced hum or buzz is equally easy to determine. Place your ear very near to each piece of your electrical equipment and again, listen for hum and buzz. If you hear a hum emanating from within your equipment, we would refer to this as mechanically induced noise (as opposed to an electrically induced noise). Mechanical hum If it's mechanically induced hum/buzz, what can be done? Plenty, and PS offers two off-the-shelf solutions: the Power Plant AC regenerator and the Humbuster AC. Mechanically induced hum is caused, almost entirely, by the transformer and is nearly impossible to get rid of (unless you own the PS Audio Power Plant or Humbuster AC). If you suffer from this noise problem, you've probably also noticed that it's intensity varies depending on the time of day, sometimes even the time of month. The reason it varies is due, in large part, to the quality of the AC line voltage and how much DC is on it. Why do transformers hum? We could use the tired saying 'because they don't know the words,' but that might get us sidetracked.  The short and simple answer is that transformers hum because of an effect known as 'lamination rattle' caused by DC voltage on the line or poor construction or both. 'Lam' rattle occurs in all transformers to some degree, that degree being related to the quality of the transformer and the quality of the line voltage.Does my equipment have a transformer? Most likely, yes. With but few exceptions, all powered electronics have a power transformer that is driving them. Why does it have a transformer and what the heck does a transformer do? Transformers serve two main functions: isolation and voltage change. Isolation is essential for your safety. You certainly don't want the metal parts of your equipment to be connected directly up to the wall socket do you? Some of us may remember as a small child the effects of sticking a butter knife or similar types of objects into the wall socket. But connect we must if we're to draw power from the utility company. A transformer connects the equipment to the power but there's no physical connection between the two, they are isolated via a magnetic field which passes the energy. The isolation provided by the magnetic field helps keep us safe. Voltage change is another great feature of the transformer. Most solid state equipment runs on relatively low voltages that range from 5 volts to 30 volts. What comes out of the wall socket is 120 volts (or 220 volts depending on your country) so the transformer reduces the voltage out of the wall to something manageable for our equipment. How does a transformer work? Transformers work with AC power. They will not work with DC power (like what comes out of a battery). This is due to the fact that transformers work on magnetic fields and the magnetic fields need to change their polarity (North to South and back again) to make the transformer work properly. What comes out of your home's wall socket is AC power. AC stands for Alternating Current, which simply means that power alternates between plus and minus voltage, unlike power delivered from a battery which has a fixed plus and minus voltage. Batteries deliver DC which stands for Direct Current. Complicated as all that may sound, it is really quite simple. Think of AC power this way; 50 or 60 times a second (depending on what country you live in) the power in your home goes positive, then negative - like a battery that flips over once every 60th of a second. This polarity change is needed to operate motors and transformers. What's inside a transformer? They're really quite simple devices, consisting of two main elements; wire and laminations. In a typical power transformer, there are two coils of wires wrapped around pieces of iron. The coils are in close physical contact with each other but are electrically isolated. There's an input coil that connects to the homes AC receptacle, and an output coil that feeds your equipment. These coil  s are nothing more than a length of copper wire wound in a circle and when you apply power to them they become magnets.The pieces of iron are called laminations. The laminations are basically small sheets of steel or iron, stacked one on top of the other. They are used to focus the magnetic field, created by the coils of wire. So, why do transformers hum? As mentioned earlier, transformers hum because of lamination rattle caused by either DC voltage on the AC line or poor construction or both. Remember when we mentioned that this humming problem was due to either power line conditions or the quality of the transformer? Here's why: when there's DC on the line, we have an asymmetrical field which causes greater vibrations. The laminations are 'pushed' together in one direction because of the DC. Because transformers work when the coil magnets switch poles from North to South and back again, 60 times a second, DC forces the input coil to always sit in one direction and this makes the transformer a little crazy so it hums. To reduce these noises, transformer manufacturer have several tricks up their sleeves: they can varnish, or use super glue to stick the laminations together so they rattle less, and they can make bigger transformers that don't have to work so hard, even in the presence of DC. The harder a transformer has to work, the more stress and strain is placed on the laminations. But these measures don't entirely solve the problem because you need to do that at the source of the problem, the DC on the line. Why this is bad When a transformer hums, it is actually physically vibrating or shaking inside of the chassis. This, in turn, shakes and vibrates everything else inside the chassis. Many components in the chassis  are sensitive to vibrations, including tubes, semiconductors and capacitors. In an even moderate case, this vibration can effect sound and picture quality as many of these internal components are microphonic and reproduce the humming into the audio or video signal.The magnetic fields produced by transformers create electrical energy in more than just the transformer. They can easily generate an electrical current in a capacitor, for instance, which is essentially a coil of 'wire' itself. It can even generate an unwanted electrical current in any wiring or PC board traces and is why transformers have to be strategically placed away from all other components. So, what can we do? We have several options: power the system with a Power Plant AC regenerator and eliminate the hum, or purchase and connect a PS Humbuster AC to eliminate it as well. We can buy equipment with better transformers. PS and many high-end audio video manufacturers go to great lengths to design and build near perfect transformers that have very low levels of mechanical hum even under the worst conditions coming out of the wall. But regardless of how well the transformer's made, we can't do better than fixing the problem properly in the first place. That's where the Humbuster AC or the Power Plants come into play: they fix the problem at the source. It's best to fix the problem at the source Regardless of how well a transformer is made it's best to keep the DC out of it. Transformers with DC on them have core saturation problems, some amount of mechanical noise and lowered efficiency. PS offers several solutions for lowering hum, eliminating DC and improving performance. The Power Plant series of AC regenerators and the Humbuster AC device. Do your system a favor and eliminate its AC problems. What about electrical noises? Electrical noises are usually caused by one of two main problems: proximity or ground loops. These hums can be identified by listening to the speaker for a low humming sound (as opposed to a buzz) or in video can be seen as a distortion of a TV tube or diagonal bars across the set. Proximity refers to how close one piece of equipment is to another. Since transformers work by generating magnetic fields, these fields can be rather large and if the field gets too close to another audio or video product, noise (hum) can be induced into the product from the transformer. This type of sensitivity is typically restricted to high gain pieces of equipment like phono stages, but even preamplifiers sitting in close proximity to a power amplifier can have hum induced into it. Solving proximity problems is relatively easy: simply move the equipment further apart. Ground loops hums are perhaps the most difficult to track down. Ground loops are a result of differing ground potentials. This means that the ground of one AC source or equipment source is at a different level than the ground of another AC source or equipment. This difference is usually amplified in the form of audible or visible hum. Visible hum is usually seen as diagonal bars across the video screen. Tracking these types of hums down is more difficult and below we have assembled some helpful tips. At the end of the day it may make more sense to speak with your dealer for help. Tracking down ground loop problems The easiest way to figure out where ground loop problems lie is by the process of elimination. You need to determine where the hum or buzz is coming from within your system. If it's a video hum problem, use a known good source like a DVD player rather than cable or satellite. In video, it's best to always assume that it's either a connection problem or, more likely, a cable problem. Our experience has shown that poorly shielded video cables cause more hum problems than just about anything else. In an audio situation, the first suspect in our hunt would be the power amp or the receiver that is driving the loudspeaker. To see if the power amp or the receiver is the culprit, turn them off, disconnect its inputs and turn it back on again. Go back to the speaker and place your ear in close proximity to see if the hum is still there. If it is, then you have a problem with your power amp or receiver and you should seek help from its manufacturer.
Just remember, take the system down to its simplest level of connection. Find a way to hook the system up with as many pieces of the system missing or not connected. Keep it simple and get it to the point where the hum's gone. Then start adding back components one at a time until the hum returns. Finding the problem is 9/10th of the work in finding a solution. Good luck and call us if you need help or use our automated Humbuster's section for more help.. |
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