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Silencing Hum: How To Tell Your Connections To Hiss Off!

Silencing Hum: How To Tell Your Connections To Hiss Off! image Silencing Hum: How To Tell Your Connections To Hiss Off! image
Parent Issue
Day
6
Month
December
Year
1974
OCR Text

ê 3 v J. 4 - s _ s % xfJm HOU 'TC 7 9 . va, r % hifi system shouldn't get away with it. Stilt, the chances are a little better than 50-50 that your system hums more than t should, despite the fact that hum s as easy to cure as any hi-fi II. And spending a couple of bucks (at most) and maybe an hour of tour time will do more to mprove the sound of your hifi system than anything short of a hot new amp or pre-amp. Why care about hum f you can barely hear t? Simply because W even a little hum not only places an added load on your system's ability to reproduce music but also mixes with low frequencies, causing muddy bass. lemove hum and bass notes will gain a new clarity and a well-defined, spacious r texture. Ultimately, hum arises from the fact that almost all hifi equipment is pow;red from the AC line. In each component there is a power supply which converts T AC to varoius direct-current (DC) voltages needed to run the device. This power suppiy can be designed to work very well (and expensively) or to opérate in a so-so fashion that will allow the manufacturer to sell his product at a higher prof t. Given the choice of gorgeous performance or a couple of cents profit, the average hifi manfuacturer will take the innoj anH nin tlio Hiicinocc icn't li-nrAn frr "hai-itw In addition to cutting corners on the power supply, many manufacturers are just careless and do things such as route the leads from the phonograph past the him-inducing f elds of the aower transformer. They know what they are doing; hum is well understood and there are lots of reasons for t- but few excuses. Fortunately, there are some things you can do at home on a rainy day that will minimize your system's hum. First, the obvious things. bpace out components. Since the phonograph cartridge will piek up hum from the magnetic field around the transformer in your components, put some distance between it and them. A few inches often make a difference, since the strength of a magnetic field (and therefore the amount of hum t can induce) drops as the square of the distance from its source. Obviously, long phono cables are not necessarily bad. Keep power and signal lines separate. It may be neater to bundie these together as they run between components, but t greatly ncreases induced hum and noise. for sale at most local hi-f i stores and are one of the few bargains n the business. Shorting plugs are nserted n unused pre-amp or receivei imputs to cut noise and they work. For proof you can hea disconnect your present phone cables, switch to this mput and listen to t with and without shorting plugs in the jacks. Sometimes, shorting plugs in open phono jacks will even cut hum on other inputs . Shorting plugs are especially useful in systems with several low-level nputs - forexample, a system with two phono nputs or an additional mcrophone or tape-head input. If your system has more than one low-level n ■ put, short any that aren't n use. Ground the turntable to your pre-amp. If you have jiist put your system together and the phono does nothing but buzz, you haven't followed directions. Run a ground wire of heavy lamp cord between your turntable's motor board and your pre-amp. If you have already done this and you still have too much hum, look for a better spot on the turntable assembly to connect to the ground. Do this by connecting one end of the lamp cord to your pre-amp or receiver and then by touching various places on the motor board. Do this while the system is on, and, f necessary, with the bass and volume up (but be careful- not too high). You'll find the connection point that gives the least hum easy to spot. Ground your whole system. If your home has honest three wire electrical outlets or hand cold-water (not gas) pipes, by all means run another heavy wire from your preamp or receiver to ground. There is one spot within your system that will give the most hum reduction; find it by connecting one end of the ground wire to the water pipe or screw holding the outlet cover on, and then touching the unconnected wire end to various components and to various spo3 on each one. Usually, the pre-amp will be the best connection point. Even f a system ground doesn't cut hum-and n rare cases t won't-you owe -y t to your body to reduce any potential shock hazard. Ground your system anyway. If you have done all this, you should have a lot less hum than you started with. There's now one final trick that will cut hum to the minimum your system can produce, and it may be the simplest step of all- flip your wall plugs. continued on page 7 I The chances are a little bit better than 50-50 that your system hums more than it should, despite the fact that hum is easy to cure. Spending a couple of bucks (at most) and maybe an hour of your time will do more to improve your system's sound than anything short of a hot new amp or pre-amp. Silencing Hum continued from page 5 Because eaclT component has its own power supply, and because these supplies interact with each other, it is possible to plug units in so that hum in one component caneéis hum from another. Make hum as obvious as possible during this maneuver by turning up the bass and volume controls. If you have a receiver complete with tuner, try shorting its inputs and listening to it at full volume on its phono input. Ditto for a separate power amplifier: short its inputs and listen to it at maximum loudness. Now, quickly turn off the equipment, reverse the line cord in its socket and raise the volume gain. There's a 50-50 chance that there will be less hum in the new position. If that's the case, get a pieceof tape or some paint and mark the plug so you know which way works best. Obviously. if hum increases, put the plug back the way it was. Do the same as you connect other components to the system-phonograph, tuner, tape deck, etc. There's one wall plu orientation for each component that will yield the least system hum. and it just takes a flip of the wrist to find it. If you have done all this, you can now sit back and listen to the music- and that's the way it should be.