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Hum from active monitors on TAC Scorpion Console.

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  • Hum from active monitors on TAC Scorpion Console.

    Hey guys, Im curious if anyone has managed to find an elegant solution to get rid of the hum out of active monitors with older non balanced outs. My console doesnt have balanced monitor outs and I have dealt with hum on my active monitors for a while. I reduced it with a ground lift significantly but never truly got rid of it. It may be a ground look somewhere though I have tried a lot of solutions to no avail and have lived with it. I even tried floating one of the wires to unbalance the plug. Didnt work. Im debating going back to passive monitors but there really dont seem to be many around and Id rather figure out how to fix it. Peter
    Stupidity in of itself is a fine art.

  • #2
    Hum, Is the hum there when nothing's plugged into them?

    If they are quiet, the first thing I'd do is make sure you don't have a ground loop. Use a power strip that has built in filtering and plug all your components into the same power strip. Keep your Monitors, computer, Interface, Mixers or any audio hardware that's being used on the same AC outlet so you don't have a ground loop. Also make sure any lines plugged into your interface aren't on another outlet.

    For example, on my current setup, I have a DI line coming from my Marshall head on the other side of the studio. When I plug it into my patch bay that feeds my Interface, it creates a hum because I have a ground loop. Same thing when I plug in the DI from my Bass head which again is on a different outlet.

    What happens is the resistance on those grounds are greater because the AC wires going back to the breaker box are longer. When I connect those amp chassis to the interface I have current flows between the two grounds because one is a shorter path. Instead of the audio amps chassis being neutral and safely carrying the stray EMF around you to ground, you have current flow through the chassis. The Chassis is a conductor for AC flow between the two grounds and the chassis emits AC EMF into the circuits.

    In my case I get around this problem using special ac line filters on those outlets. I work in the electronics industry and sell filters for all kinds of Office equipment, computer, networks etc. I use 1:1 Isolation transformer type filters on those outlets which completely disconnect the gear from the main line. The grounds are connect via caps so they are essentially lifted. It doesn't get rid of all the hum but its low enough where its barely audible. I have too much gear in the studio to put everything on the same outlet so I found this to be the best solution.

    Of course when I'm mixing I remove those interface inputs and only deal with the small level of hum that was on those tracks. My monitoring system is dead quiet mixing. I do use unbalanced inputs to my monitors too. I did make sure I bought high quality cables to feed my monitors too. When I first bought them I tried them out with cheap RCA cables and 1/4 to RCA adaptors. Between the vibrations on the monitors and the poor quality cables I'd get noise and crackles so I quickly upgraded to some goo 90% shielded cables and have been good ever since. I use a switch box to switch between or combine several different sets of monitors and having good cables is a given. Nothing worse then hearing a pop or hum and then having to dig through all those cables to find the offending culprit.

    Not sure if these suggestions apply, but having everything on the same outlet is priority one. Second would be to make sure you don't have gear sitting on top of power transformers. Some gear has built in transformers for converting AC to DC. The position within that piece of gear may be fine for that gear running noise free. If you place another piece of gear close to where that transformer is within that chassis the EMF may escape and regenerate in another piece of gear. On a crowded work station your may have two pieces of gear too close together and just by moving one you can eliminate the noise. Something like a Computer or Monitor power supply are often the culprit around sensitive audio gear so having enough space between the chassis is the key.

    A trick I use is I have one of those old head demagnetizers I used for demagnetizing my tape heads. It makes an excellent EMF probe. I can plug it in and run it around my audio cables and connectors with my gear cranked up. If I get it near a weak cable shielding or connectors I can easily hear the AC it generates and find the weak spots in my setup. (Of course you want to keep it away from Hard drives and devices that could be damages by ac waves)

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    • #3
      Sorry for the slow reply. So here is the interesting thing. My actives monitors have a slight hum not dead silent. Everything is plugged into a furman pl-plus conditioner. I am guilty of having some smaller things plugged nearby but I experimented with a few things. I plugged the monitor into just a ebtech hum x. No change. I then plugged it back into the furman and plugged the furman strip into the ebtech no change. Then I moved the power supply for console to a different plug across the room and used the ebtech on it. No differences. Now that said I forgot to mention in this that my hum increases substantially once I turn on the console. Turns out that the auxiliary monitor outs per my manual are balanced where the primaries are not. However i have to take this on faith bc my manual is for a scorpion II and I have the scorpion I which was earlier. Not sure if that is different on the outs but I think not. I do have very good cables. I purchased a small length pair of high end Monster cables that I plug into my PDB passive direct box which offers the ground lift and is a marked improvement but no where near silent and the hum is present.

      I have to note that we had this setup in a different location with my older Mackie 824HR monitors and we had the same issue. My drummer at the time got past it by running the monitor amps through an equalizer unit on bypass. I have to chat with him since its been a long time if it was totally silent then. The house is less than 5 years old and I had an electrician check and tune the circuit box and install a surge protector there as well. Im a bit stumped and trying to figure out how to get rid of this or if I have to just live with it. I was thinking of trying a different lift unit from another company such as ebtech or even a higher end conditioner unit from Furman that may offer further isolation.

      PS my mac and monitors are on the other side of the room. Im attaching the console pic so you can see the way I have it laid out. The desk with mac and monitor is on the other side of it so I can just turn around and mix etc. Its a problem for sure I have yet to find a solution this damn hum. I have a super old alesis eq that I could test the solution my drummer did but it would probably just add more noise. Its like 20+ years old and collecting dust indefinitely.
      Stupidity in of itself is a fine art.

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      • #4
        From your explanation it seems your console is what's producing the hum, not your monitors. One way to check is to plug the console outputs you have going to the monitors to something else like a headphone amp and see if the hum is still there.

        If it is, you can disconnect all inputs one at a time to see if its a ground loop or something going into that board. If all inputs and external gear is disconnected and you still have a hum then its likely an issue inside that console. It can be anything from cable routing to an oxidized connector. Filter caps are a common thing to go bad too. Normally you can get 10 or more years out of a set of filter caps but you can have one leaking AC into your DC supply at just about anytime. A common scenario is it begins with a very low level in the background and gradually gets worse over time. Not all boards are built or designed well too. Some boards can get a great reputation for being a workhorse and every once and awhile one has a flaw. A component gets overheated when installed which weakens its lifespan, or something gets zapped. Cracked solder joint or whatever.

        Many times we ignore the elephant in the room just because we paid allot for it and expect its quality to be top notch. To me from what you described, it sounds like there's something leaking ac into the DC circuitry of that board. Troubleshooting dictates you work from one end of the chain back one stage at a time till you find the cause. If you have no hum going in and have hum coming out, you pretty much narrowed the cause down already. Whether something can actually be done to eliminate it may not be nearly as easy.

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        • #5
          I actually have gone down that rabbit hole a bit. From the headphone outs and the channel strips not a hum. Its specifically in the monitor outs. That said, my former drummer said he conquered it going through a dbx eq unit and leaving it on bypass. Interesting. I have toyed with the idea of taking the console to a repair shop that I know of and saying just find it and fix it. But this thing ways a ton and its not exactly easy to export. im pursuing a few leads. ill keep ya posted.
          Stupidity in of itself is a fine art.

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          • #6
            I looked at the schematic a bit. It looks like some outputs like the Aux sends have a buffer just before the outputs jacks. Others like the direct out and monitor sends don't have those same buffers and may have a considerable amount of wiring within the mixers chassis, especially the direct outs which tie directly into the main buss.

            Your key clue here is you say the hum goes away when you add an EQ in bypass mode. That bypass mode is probably not true bypass and you have some 1:1 buffers running in that EQ so the monitors are essentially decoupled from the mixer and no impedance loading is occurring.

            Since your mixer doesn't have balanced outs and your monitors do have balanced inputs there are a couple of things you could try.

            One might be to use impedance matching transformers like these. http://www.parts-express.com/xlr-fem...ormer--240-396 Thee are some that have a flexable wire on the 1/4" end too if that is needed.

            The transformers will convert the high Z unbalanced to Low Z balanced. The sound quality should be pretty good. Shure makes some with Jensen transformers which are noted as the best for passive fidelity but even with these budget versions it shouldn't color the sound much if any. The benefits of being able to run low impedance cables may more then enough to make up for any high frequency losses.

            You can probably do the same thing with passive or active DI boxes. Passive DI boxes do have a ground lift which can be tried, and they do have a built in attenuator switch. Main thing is they too have transformers which should isolate any loading that's causing the hum and you can run unbalanced in and balanced outs.

            A Passive DI may be the best of the bunch because you'll be adding buffers like you did using the EQ, You'll have to do some research to find the best stereo unit, but there's a bunch of them that provide high fidelity. I'd just look closely at the specs and try and get something with low harmonic distortion levels and a flat frequency response so your sound quality remains transparent.

            There are some other options too. They make Headphone amps that can be placed between the board and monitors that may be buffered.

            I think most studios prefer to use a line level distribution amp to drive several sets of monitors. Radial is a well known distribution amp that also buffers the signal. http://www.radialeng.com/chaindrive.php They aren't cheap and there may be less expensive options that will work just as well, but I think something like this might be exactly what you're looking for. The outputs are being loaded down for some reason causing that board to hum so you don't have many options there as a fix. I cant say your problem is unusual. In my days as an electronic tech that defies logic and other then redesigning a piece of gear or modifying it some how, you have to use the solutions which work. You seem to have that solution and by adding a quality buffer it looks like you can achieve your goals.

            I would try the passive line matching transformers first. If they work you're only out $20. If that don't there's a ton of other things you can use them for including converting a guitar cord from high to low impedance and back again. Just be sure to check and see if the Male/Female match your cords when connecting to your monitors. I know it works with a mic but I'm not sure if your monitors have an XLR, Male, Female or TRS. You can get or make adaptor to match those of just swap the connectors out on a mic cord.

            Hopefully one of these should work. Good Luck.

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            • #7
              I already have a DI with a ground lift connected. It reduced it quite a bit but not 100% so im not sure the transformer plug will give me much more. The interesting thing here is that when I was messing around I moved it to another spot and the sound got better. When I touched it the hum pretty much went away. That has me thinking its literally a ground issue on the console. I also wondered if maybe I didnt have the best DI (ART 2x) but I dont think thats it. Its a conundrum for sure.
              Stupidity in of itself is a fine art.

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              • #8
                Oh per the manual the alt monitor outs are balanced but the hum is the same.
                Stupidity in of itself is a fine art.

                Comment


                • #9
                  It looks like that power supply is separate, vs being built inside the console itself. This means the cable between the supply and console carries DC voltage. That cable should be well shielded so stray EMF doesn't get carried into the units amp circuits. In other words, that DC input can act like a radio antenna to carry ac noise into the unit and get amplified. When you move the supply around its like moving a radio antenna around. Ever take an AM radio and put it close to an AC source and hear it hum? Same kind if thing here.

                  When you touch the chassis and the hum level dips, your body becomes earth ground and acts as additional shielding.

                  How bout this. You get a big flat metal plate to set the unit on, then ground that plate to your outlets ground. That should absorb a huge amount of noise. As a quick check, you can also take tin foil and wrap it around that DC voltage cord and ground it to see if there's any improvement. Aluminum foil is a poor shield for EMF. It works very well at high frequencies but passes too much AC for audio but you should hear some improvement. (plus you cant solder wires to aluminum, only weld them) If you do, then get copper foil as a replacement and it will work 3X better to block noise.

                  You do have AC wires running through walls and across the ceilings so you may have allot of emissions there. In office type building they run AC wires through grounded pipes. That console may have been designed to be used in a studio where they have that kind of professional conduit. In a house you just have cables with nothing but the ground wires.

                  All your outlets in a home have either screw or clip type connections on the outlets. They may not provide the best continuity. Same thing with the breakers in your box. They just use clips to hold them in place by pressure. The ground ends at a rod pounded into the ground with a cable attached by a screw on clip. The rod is often brass and brass can tarnish providing a poor ground. Taking some sandpaper and removing that tarnish at the connector can provide a solid ground again.

                  Using an volt ohm meter is another useful tool. Set it for ohms and test between one piece of gears frame ground and another, like the chassis of your console and the chassis of any other piece of gear will tell you if the cables connecting the two pieces of gear are doing their jobs. You can also set it for low AC volts and see if you have any voltage between them. Try it with then connected and disconnected. If you get a higher voltage with then disconnected then you have an AC ground problem.

                  Other things that can help you isolate the problem. If you can get your hands on one of those tape recorder tape head demagnetizers, and use it as a probe to find where the leakage is occurring. You crank the gear up so you hear the hum then go around the unit and its cables like a Geiger counter and when you have a weak area the hum should increase. Be sure to keep it away from your computer and actual chips on boards. You don't want to erase a hard drive or erase data on a chip, but its safe to try this on your cables.

                  AC noise is getting in on either the DC voltage or a signal wire and being amplified so those are your most likely suspects.

                  Another sore spot is a computer monitor. The old CRT monitors had huge AC emissions because of their fly back transformers. Many LED monitors are just as bad. Much better then CRT but some of the old ones were still pretty noisy.

                  The power supply inside a computer can be awful too. Laptops use an external brick and Desktops use internal switching supplies. These power supplies are designed to work fine on computers because they are digital and the emissions don't effect their processing. Get them around sensitive audio gear and you can have allot of noise. Computers circuit boards receive voltage even with the computer turned off so unplugging them may be a test.

                  Be sure you take the excess cables and tie them up with twist ties or tie wraps too. Having excess cable neat and orderly will prevent hum transference between cables. Just having one lay on top of another can add to the problem and make it more difficult to isolate.

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                  • #10
                    Finally I have conquered this. Not the ideal solution but what finally did it was my tac monitor out to a ground lift into an ebtech hum eliminator xlr. Since its the monitors I dont care so much because all my channels and groups are clean. Slight hum still but barely audible. Im happy with this even if it was frustrating as F***.
                    Stupidity in of itself is a fine art.

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                    • #11
                      Well all the TAC shorted out and is DOA finally. Solved the issue by buying a new console. I know have the QU-32 and while it has a few things I dont like such as hard set sample rate and USB2 instead of USB3 everything else is fantastic. The Scorpion now sits in the garage while I decide what to do with it. BTW new console is so quiet with monitors Its like the tin man. Its a digital console with a heart of analog in design. Thanks for all the thoughtful advice previously given. Peter
                      Stupidity in of itself is a fine art.

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