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Hum and Ground Loops




Hum


Hum and noise are part of the audio experience. We’ve all experienced them. In fact about a third of our conversations with our customers are about solving hum problems. But how do you get rid of them? In this Tip we’ll talk about a few techniques that usually work with Omega Mikro and Clearview components.

 

Ground Loops:


The most common sources of hum and noise are ground loops. Ground loops can develop whenever two components share AC outlets that are at different ground potentials.  This causes a current to flow between the two components: which is like mixing a second signal with your desired audio signal.  You hear the mixed-in hum and noise and it’s annoying. Dual mono amps are especially susceptible to ground loops if the two amps are plugged into different ac outlets.


Here are some ways to beat the ground-loop problem. The simplest way is to plug all of your components into a single AC outlet. You may have to use a multi- outlet power strip to solve your particular problem.  These cost under $10 and will demonstrate the problem can be cured (or not) by a single ground. If it does, and you can live with your system sounding slightly degraded but hum less, that’s great. But few of us want to hear the degradation caused by a generic power strip so consider a Clearview Power Strip or Omega Mikro Power Central or Stratum after you’ve determined that a power strip will solve the problem.


Another way is to have an exclusive, single, ground rod connection for all the outlets you use for your audio/video system.  Everyone that ‘s installed one of these reports the same benefits - even if they had no ground loop or other hum problems to begin with - the background is noticeably quieter, musical details are rendered with greater clarity, and micro-transients and leading and trailing edges have greater realism: the music is more like live.


Still another but slightly dangerous but also effective way to beat the effects of ground loops is to lift the ground connection on each component using a cheater plug. When you lift the ground on a component its chassis ac potential (voltage) can rise high enough to give you a bite - especially if you touch it with one hand while your other hand is touching another component. This technique will also slightly degrade the sound but you may be able to live with it if it gets rid of your hum and noise problem.


If you choose to assume the risks of cheater plugs start with your dual mono amps. Lift one ground at a time then listen. Continue lifting grounds working from the amps, to your preamp, then your sources, until the hum and noise are acceptable. We recommend using the same ac duplex outlet for your CD transport and D/A.  Even if you don’t think you have a ground loop problem this will produce cleaner sound.


Some of our customers have balanced amps and preamps.  Balanced interconnections avoid the effects of ground loops by rejecting ground loop currents. But they do this at the expense of degraded sound from the balanced topology. When they try to go unbalanced they then experience the effects of the ground loop. In every case, when using our interconnects in an unbalanced connection and by solving ground loop problems with the tricks above, the customer reported significantly better sound.

 

Local Electromagnetic Fields:

 
Some of our customers live near a high power transformer or have leaky transformers in their equipment or in nearby electrical devices.  (Almost all transformers emit stray fields). Fluorescent lights (even the new compact ones) can be sources of hum and other degradations too. If you can’t turn these offending devices off then you may want to consider the following.


1. First, low power signals are far more susceptible to external hum than higher power signals. So the most vulnerable interconnects would be between the output of a moving coil cartridge and its phono preamp. Speaker cables would be the least susceptible.

 
2. Once you’ve isolated the interconnect picking up hum (the victim interconnect in EMI jargon) try changing the distance between the two ribbons  - push them closer or spread them part.  We’ve had cases where moving the interconnect two inches totally eliminated a strong hum.  If simply moving or spreading the interconnects doesn’t solve the problem try orienting the plane of the loop formed by the two ribbons at various angles. We’ve been able to use completely unshielded AVII’s between a low output moving coil and high gain phono preamp by orienting this plane so that it cancels the hum- completely. Once you’ve found the plane of cancellation you’ll then have to figure a good way to keep it there without introducing a lot of stray dielectric.

 
3. The earth is literally bristling with hum and noise currents. The Omega Mikro development lab is built on a floor a few inches from earth. The currents are so strong that if we lay even a high-level signal cable on the floor we’ll get hum. Fortunately the solution is simple - keep all interconnects, power cords and speaker cables at least a few inches from basement or ground level floors.