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A/B box hum? NOT ABY!

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  • #1

    A/B box hum? NOT ABY!

    I just recently aquired a JC-120 to use for clean tones and figured I would use an a/b box to switch between the two amps... not an aby to use both at the same time.

    beavis audio research
    http://www.beavisaudio.com/projects/ABSwitches/AB_Simple.gif


    I looked up the plans for it and fulltone has one, as well as general guitar gadgets and beavis audio. I built the box as to these directions, which includes grounding out the input to the amp not being used.

    No matter what I seem to do, I get some horribly nasty BUZZ and HUM especially if I place my fulldrive 2 after the ab box and have it on while playing clean into the JC-120.

    I tried with a 3pdt switch and a carling dpdt switch (I don't use any LED's) and same results both ways. I am assuming it's a ground loop, but most of what I read says this design doesn't worry about these as I'm not running both amps at the same time and I have no desire to at all!

    Any advice? I really don't want to buy a crazy expensive switcher...
    Political Correctness is a doctrine, fostered by a delusional, illogical minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.
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  • #2
    Re: A/B box hum? NOT ABY!

    I'm so totally not technical so I don't have much help to offer other than this:
    Hopefully the Humdinger will solve your problems, althought I've never used one.


    If I know I'm going crazy, I must not be insane.

    Originally posted by TheLivingDead
    DON'TGETMADBRO

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    • #3
      Re: A/B box hum? NOT ABY!

      Originally posted by xxxplorer View Post
      I get some horribly nasty BUZZ and HUM especially if I place my fulldrive 2 after the ab box and have it on while playing clean into the JC-120.
      I'm not sure about the AB box, but this is definitely a problem. JC120's are NOT meant for any kind of dirty playing. Tried it once, never again.
      Custom neck-thru strat
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      Roland RE-201 Space Echo, 70's Fender Reverb Unit

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      • #4
        Re: A/B box hum? NOT ABY!

        That humdinger looks cool. Anyone know of other similar devices?

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        • #5
          Re: A/B box hum? NOT ABY!

          No no... Jc-120 is only used clean. I have my cord into the a/b box, then channel a into the jc, channel b into the fulldrive and marshall.
          Political Correctness is a doctrine, fostered by a delusional, illogical minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.

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          • #6
            Re: A/B box hum? NOT ABY!

            I use two amps as well. When I first did it I used a Marshall 900 combo A/B'd with a Super Reverb. For the most part it worked well. I used a Morley A/B/Y & the Morley pedal really sucked! I tried many different A/B & A/B/Y. IMHO the best is a Lehle. They run about $350. I almost ordered one but I decided to try a Loopmaster A/B/Y. The Loopmaster really eliminated most of the noise & it was like taking a blanket off my speaker cabinet. The tone was much cleaner & more defined. I also added a HumX on bot amps. The HumX removed about 90% of the hum.


            What it sounds like is you are getting a ground loop hum. The Lehe A/B/Y has ground loop transformers built right into the pedal so it is dead quiet. Radial also makes a couple of pedals that also have ground loop transformers in them. Ground loops need to be addressed, generally when you are running two amps they can also operate at different frequencies causing the noise. I recently had some work done on one of my amps and suddenly the amp was much quieter. The fact is my amp(s) were never noisy except when I was in the drive channel, but playing through the the "other" side of the A/B box. You could hear the "hiss" of the drive channel. This is normal and should not be considered a problem.
            Last edited by Bludave; 02-14-2012, 07:17 PM.
            "So you will never have to listen to Surf music again" James Marshall Hendrix
            "When the power of love overcomes the love of power, then the world will know peace."-Jimi Hendrix

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            • #7
              Re: A/B box hum? NOT ABY!

              It sounds like you are getting a ground loop from running both amps. Radial makes a few a/b boxes that have isolated outputs and ground lifts. That should take care of the problem.

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              • #8
                Re: A/B box hum? NOT ABY!

                years ago i tried a morley a/b box and had same problem. Was absolutely unusable. I purchased the framptone, problem solved , very happy. I bought the 3-amp model. Absolutely silent.
                Attention Required! | Cloudflare
                http://framptone.com/

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                • #9
                  Re: A/B box hum? NOT ABY!

                  I'm running one at a time, never both 'on' at the same time. Should I isolate all the jacks from the metal casing?
                  Political Correctness is a doctrine, fostered by a delusional, illogical minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.

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                  • #10
                    Re: A/B box hum? NOT ABY!

                    You need a Radial Amp Bone.

                    Bill
                    When you've had budget guitars for a number of years, you may find that your old instrument is holding you back. A quality guitar can inspire you to write great songs, improve your understanding of the Gdim chord while in the Lydian Mode, cure the heartbreak of cystic acne--and help you find true love in the process.

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                    • #11
                      Re: A/B box hum? NOT ABY!

                      Eric Johnson uses the same circuit... Why does mine not work?
                      Political Correctness is a doctrine, fostered by a delusional, illogical minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.

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                      • #12
                        Re: A/B box hum? NOT ABY!

                        Originally posted by xxxplorer View Post
                        Should I isolate all the jacks from the metal casing?
                        Yes.
                        If that doesn't work out for you and you still wanna DIY, BYOC makes a this.
                        MM

                        2000 ES335LE Teal Blue, 2009 Gibson LP Trad Pro HCS, 2007 Edwards LP-130LTS/RE Lemon Drop, 2010 Gibson '50's Tribute Studio Goldtop.
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