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Advice/troubleshooting help on this noise issue

Discussion in 'Effects [BG]' started by Adamixoye, Sep 26, 2013.


  1. Adamixoye

    Adamixoye A PT Pro is cool for worship, right?

    Apr 9, 2012
    Occasional Beta Tester for Confusion Studios, Singular Sound, and Source Audio
    I have a combo bass/guitar board with ~10 pedals. I have isolated one of the most significant sources of noise to the interaction of two pedals.

    The first is a Morpheus Droptune. It is digital, allegedly true bypass, and needs a 12V center-positive power supply.

    The second is a Hardwire TL-2 (their take on the Metal Zone). It is analog, allegedly true bypass, and takes a standard Boss-style PS (9V center-negative).

    Here's the issue: when the Morpheus is in bypass and the TL-2 is on (at pretty high gain; it knows no other setting), I hear a high-pitched hum. Not gain hiss, but hum. The TL-2 is my most high-gain pedal, I haven't fully tested whether I can replicate this with my other dirt pedals (B7K, Empress Multidrive). When I engage the Morpheus, the noise largely goes away.

    Now let me be clear: I don't really understand the practical electronics involved. I barely know what a "ground loop" is. The question I have is, given these circumstances, will a filtered, isolated power supply help, or is something going on with the Morpheus and/or my board arrangement that will create hum no matter what I do?
     
  2. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Yes an isolated-outlet power supply will almost certainly fix or improve the problem you described. Even with that there is a possibility of some interaction between the pedals via the patch cord shields, so there are no guarantees--some pedals are just plain never going to work together. But the first step is definitely to isolate the power supplies, and odds are pretty good that it will work.
     
  3. Adamixoye

    Adamixoye A PT Pro is cool for worship, right?

    Apr 9, 2012
    Occasional Beta Tester for Confusion Studios, Singular Sound, and Source Audio
    Thanks for the response. I've been debating whether or not to bite the bullet and buy an expensive power supply. I don't have the most pedals, but I have several high-current pedals of various voltages that would necessitate something like a Pedal Power Mondo (if I wanted to cover everything). Right now I'm using wall-warts into power strips, plus one daisy-chained 1Spot for the low-amperage 9V center-negative pedals.

    Do you have a layman's explanation of why, if the issue is non-isolated power, it happens when the pitch-shifting pedal is in bypass but not when it is engaged? I know that daisy chaining opposite polarity pedals off of the same power supply can result in 60Hz hum. I would have assumed that perhaps the two opposite polarity power supplies, even if not daisy-chained, might have interacted somehow. But the bypass=hum, engaged=mostly quiet nature of the problem didn't make sense (again, given my admittedly limited knowledge of the electronics).
     
  4. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    The issue is "potential". A voltage only exists as an amount of difference relative to an arbitrary reference point. That reference point is "0 V", however there is no such thing as 0 V really--we just take the ground wire and call it zero. But if you compare that ground wire against the ground in another device, there may be a measurable voltage difference between them! This voltage is called potential, and it has to go somewhere--so it often ends up bleeding into the audio path, and we hear it as noise or hum.

    Since all pedals share a ground path via the shields of the patch cords, there is always a possibility of unwanted potential noise even if the power supplies are isolated. However the problems become much worse if the potential is amplified by feedback. A ground loop is feedback, like the feedback between a mic and speaker, only existing on the ground planes.

    Regarding the on/bypass difference, the circuit potentials change depending on the bypass status.
     
  5. Adamixoye

    Adamixoye A PT Pro is cool for worship, right?

    Apr 9, 2012
    Occasional Beta Tester for Confusion Studios, Singular Sound, and Source Audio
    Now the question is whether to bite the bullet and see if a power supply will solve it (it helps that I want a power supply anyway)...
     
  6. ledyard

    ledyard

    Jan 31, 2010
    Upstate NY
    With 10-ish pedals I assume you have tried moving the pedals in all different sorts of orders?

    I would assume again, maybe I'm wrong that the extra ground frequency that has to go somewhere is the difference between the 9v and 12v power supply? Have you tried the Droptune at the very beginning and at the very end of your chain? While the problem is still most likely the power supplies it couldn't hurt.

    I assume you have plugged different basses into it to eliminate that possibility? (hey....just checking....it happens)

    Possibly the Morpheus isn't really "true" bypass? Leaking some nasty frequencies that are amplified by your Dirt pedal? I have seen that with my guitarist's pedal board before. At least that's what the mod guy described to me as he modded one of the pedals to true bypass.
     
  7. Adamixoye

    Adamixoye A PT Pro is cool for worship, right?

    Apr 9, 2012
    Occasional Beta Tester for Confusion Studios, Singular Sound, and Source Audio
    Well, I haven't mixed the pedal board up too much. There is a definite order that I want things in. The Droptune is at the beginning and the TL-2 is somewhere in the middle. The Droptune doesn't really work anywhere other than the beginning.

    Like i said it's my guitar/bass board and the issue is the same for both.
     
  8. ledyard

    ledyard

    Jan 31, 2010
    Upstate NY
    I understand that things definitely sound different when placed in a certain order.

    Other than the obvious ground issue I'm wondering, again, if one is not really true bypass.

    Is the 12v pedal the only pedal on your board that has a 12v power supply?
     
  9. ledyard

    ledyard

    Jan 31, 2010
    Upstate NY
    Is your pedal board one of the ones that has plug ins on it for each wall wart? Or does it have the small jacks like the pedals have and you run double "jack" ended cables from the pedal to the power strip?
    Or....is it a home made pedal board? With just a power strip?
    Sorry (face palm)I was automatically thinking it was one of those SKB style pre made boards with a power supply section. I'm so used to seeing my two guitarists boards that I just assumed.
     
  10. Adamixoye

    Adamixoye A PT Pro is cool for worship, right?

    Apr 9, 2012
    Occasional Beta Tester for Confusion Studios, Singular Sound, and Source Audio
    I have another 12V pedal (Markbass Supersynth).

    I have read very interesting things about how not all pedals advertised as "true bypass" truly are. I do wonder about these.
     
  11. Adamixoye

    Adamixoye A PT Pro is cool for worship, right?

    Apr 9, 2012
    Occasional Beta Tester for Confusion Studios, Singular Sound, and Source Audio
    I have two cheap power strips mounted under a PT Pro. I use wall-warts for all the high-current/non-standard voltage/positive polarity stuff. All 9V low-current center-negative stuff is off of a 1Spot.
     
  12. ledyard

    ledyard

    Jan 31, 2010
    Upstate NY
    When I used to have a Boss OD1 and a crybaby, I had them modded for bass. I also had them modded to be true bypass. My tech said as far as signal sucking and order of pedals on a board ect, it can make a difference.

    I would try, just for giggles, moving the Morpheus to the end just to see what happens in regards to diagnosing your hum issue.
    I would also try putting batteries in the Morpheus if you can just to see what happens with the hum. I would also try running an extension chord to another room where you know it wont be on the same breaker in your house and plug just the Morpheus into that. See if that solves it. heck, even try the battery thing and the extension chord thing with the Distortion pedal too. Just to eliminate all the options concerning the grounding. Or most of the options anyways.
     
  13. Adamixoye

    Adamixoye A PT Pro is cool for worship, right?

    Apr 9, 2012
    Occasional Beta Tester for Confusion Studios, Singular Sound, and Source Audio
    The Morpheus does not take batteries, but I can try a battery in the Digitech.
     
  14. ledyard

    ledyard

    Jan 31, 2010
    Upstate NY
    Cheap power strips obviously can be a problem. But you know this already.

    I would try some of the little things I mentioned just to see if you can get something to change. That might give an indication of an easy fix or really let you know that you just need to spend the money on a nice power supply that you already want.
     
  15. Adamixoye

    Adamixoye A PT Pro is cool for worship, right?

    Apr 9, 2012
    Occasional Beta Tester for Confusion Studios, Singular Sound, and Source Audio
    My biggest fear is not so much that I can solve the problem another way; my biggest fear is that I spend $200+ on a power supply and the issue is something else.
     
  16. ledyard

    ledyard

    Jan 31, 2010
    Upstate NY
    :D Exactly why I was trying to give you all those options to try and diagnose it even further. Even a pedal mod to true bypass wouldn't cost anything near a new power supply.

    Also... just for giggles and process of elimination have you tried swapping out patch cables?

    Also removing the two pedals from the board and running them together and seeing how they react.
     
  17. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    That, but also the difference between one "zero V" and another "zero V", neither of which are truly zero since there's no such thing. IOW this kind of problem happens all the time even when all your pedals are 9V.
    The thing is, there are many ways to make true bypass. When one of them doesn't work properly in a given rig, the average confused dude and the typical hack modder will say "oh it wasn't REALLY true bypass".
    Put a battery in each of the 9V pedals, and continue to use the individual wall warts for the non 9V pedals. This will sort out for sure whether isolated outlets could help, for only the cost of some batteries.
     

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