Humming noise
From Ssl-wiki
Contents |
Introduction
This article gives some tips how to get rid of hum noise while using SSL.
Start
There are a few common causes for noise and hum. Following is a list of things you should double check.
Length/location of cables
(Taken from here, Steve W. from Rane)
- How long are your unbalanced cables and what physical path do they take to get to their destination? Perhaps they're running next to a large hum field and picking up hum? Just move the cables physically around to see if the hum changes.
(Taken from here, Steve W. from Rane)
- Certainly, if you try to use unbalanced (RCA or unbalanced 1/4") cables for the above long distance application you're asking for nasty hum. This is why you cannot buy RCA cables that are longer than 12 feet, you'd get hum every time. This is where balaned audio interfaces can solve the problem. In fact, it's why balanced audio has existed since the 1920s and before.
- If you use balanced audio outputs feeding balanced inputs AND the two pieces of equipment you're interconnecting do not have "pin-1 problems" (See here for more details), you'll be in good shape and will typically not have hum problems at all. If you do have hum in a balanced interconnect, you either have a product with a pin-1 problem, you need better/tighter twist in the audio cable, you need better internal balanced audio circuirty, and/or you need a good audio isolation transformer.
Wrong Gain structure
(Taken from here, Steve W. from Rane)
- Another possibility perhaps: how's your gain structure? Poor gain structure is the #1 cause of hum and hiss. See here If your amplifier is turned up all the way, you may be creating the problem.
Ground loops/proper grounding
(Taken from here, Steve W. from Rane)
- Was the audio system (mixer & amp) earth grounded? If your mixer has a third pin on the line cord AND the AC power outlet had a third prong that truly was grounded at the AC circuit breaker panel, this MIGHT have helped a little. Another complication is the turntables and their need to be well grounded (to the mixer/phono input).
- You might have tried to plug the light into a different outlet (different AC circuit breaker) just to see if it reduced the problem (probably would not)...
- SSL passes all the FCC, CE, CSA, UL and other government agency approvals for emissions, sucseptibility and immunity [to what the governments say are "safe" standards]. We have all the test result graphs at the office up into the several GHz frequency range. The trouble, however, can sometimes be that you're in a situation that exceeds what the government tests to. In other words, the light is tested to a very different set of standards than an audio system/product is.
(Taken from here, Steve W. from Rane)
- If two pieces of equipment use different AC outlets, especialy outlets that are physically far apart or are on different circuit breakers, the potential for hum, buzz and noise that is not the desired audio between your devices is increased.
General breakdown
(Taken from here, Steve W. from Rane)
- Let's assume it's noise pick up. [You won't hear the hum noise in your ears obviously, but the cables pick it up.] All unbalanced interfaces (and I do mean ALL) experience this phenomenon to some degree. Unlike 99% of unbalanced interfaces, yours unfortunately is bad enough that it's making you pull your hair out. The interference is picked up in loop areas. What this means is, if you were to spread out the cables (farther apart from each other) the noise gets worse. Conversely, if you reduce the loop area, the noise is reduced. Despite what Monster Cable marketing tries to tell you, thicker audio cables do not help. Thicker, better RCA shields do not really help either since the "shield" in such a cable is not a shield at all because it carries the return audio current. (Disconnecting the shield will prove this to you since the audio will go away.)
- A "loop area" example so you can wrap your head around what I mean: I'm not sure if you remember the 1970s when a popular and important product for studios was a magnetic tape eraser. here's an example: datalinksales.com This is a device that you plug into the wall and it produces a very large, very powerful electromagnetic field which, when brought physically near magnetic tape, erases the tape. If you had one near your unbalanced audio cables, you'd pick up nasty hums and noises, thus these are nice troubleshooting tools if you're experiencing noise pickup in systems. [You don't need one to solve your problem, I'm just heading somewhere for this loop area idea.]
- [Don't do the following, I'm just continuing the loop thing] If you were to remove the plastic jacket on any RCA cable, you'll find a cylindrical conductor "shield" and inside it is another wire conductor. These are connected to the shield and tip, respectively, of the RCA jacks at the ends. If you could take these two conductors and physically separate them, thus creating a loop with RCAs on the ends, the more you separate the wires, the more noise you'd pick up if a magnetic tape eraser [or anything that uses electricity] were nearby. The closer they are to each other, the less noise you'd pick up if your tape eraser was nearby.
- By putting the inner conductor inside the outer one, this design reduces the loop area pretty well. So, new cables with this design won't get you improved noise immunity since the loop area cannot be improved (unless you move to balanced, twisted cables plus a shield - but let's not go here yet - it's not necessary).
- OK, so for single RCA cables and stereo pairs that are molded physically next to each other, you cannot reduce the loop area. You can however consider the multiple RCA cables required to connect your entire system together as addition "loop areas," each of which contribute a tiny bit of noise. For example, unplug all but one channel to prove to yourself that reducing the total number of connected cables reduces the overall noise.
- By taking all the individual pairs of RCA cables and physically routing them as close to each other as possible, you'll be reducing a variety of the various loop areas in your audio system. This might decrease the noise a little bit. Perhaps enough, but perhaps not.
- Next. Something in your system is generating the noise. If you can figure out what the source of the noise is (a wall wart, power supply in or out of a piece of hardware or an amplifier's power cable or...?) and physically move it farther from the cable(s) that is(are) picking up the noise, you'll improve the noise considerably. Have you tried turning off lights or other things nearby which may generate this noise?
- Next. Since you cannot reduce the loop area of the cables you have, shortening the overall length of the cables can help some (since it effectively reduces the total loop area). This means using a 1 meter RCA cable versus 2 meters will reduce the noise by half. The shorter the unbalanced cables, the better. Only a few companies make REALLY short cables (<0.25 meters), but these are good things, even though they charge too much for them. Make your own if you have the gumption. There's a good reason you cannot buy an RCA cable that's more than 4 or 5 meters long, they'll have so much loop area when in use that they're very likely to pick up noticeable hum and noise. (This is where balanced audio cables - like mic cables - come in which allow quite long lengths without appreciable noise pickup, yet mic circuits and balanced XLR circuits have major major advantages over unbalanced circuits. Since your interconnects are all unbalanced, it doesn't make much sense to go to the trouble of using twisted pair mic cable - 3 conductors where the third, outer conductor truly is a shield.)
- Have you determined if it's only one channel that's noisy? I forget.
- If all these things fail to reduce the noise enough, I wonder if you have a friend that's got an SL 1 you can simply try in your system? If nothing but the SL 1 changes and the noise stays, it's your system and not a broken SL 1? If it's a broken SL 1 box, we'll work on fixing it quick. Every SL 1 we ship is 100% tested and left here working.
Links
Acknowledgements
Credits for this article go out to:
- nik for adding
