Weird Electrical Problems With Stereo Rig

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Jack Harris, Jun 17, 2019.

  1. Jack Harris

    Jack Harris Member

    Messages:
    3
    Joined:
    Jun 17, 2019
    Alright. So I have a 4104 combo amp and a twin reverb that I have going in a stereo rig. Everything seemed fine, but I rearranged my pedal board because I got a CS12 power supply and got rid of most of the daisy chains. I’m running 17 pedals counting the tuner, but I never noticed this issue when I was running the daisy chain (just the horrible hum is all hints the one spot iso supply) and I have never heard of this problem before- when I have my Marshall plugged into any other available plug in my garage my TWIN starts to crackle. Now I know my Marshall needs to be serviced (tubes crackle a little when it’s warming up) and I JUST had the tubes replaced in the twin and it happens when everything is unplugged so it isn’t my pedal chain and everything is plugged into power conditioners or surge protectors coming out of a power conditioner. Even when the Marshall is off but the plug is plugged in it still crackles (in the twin) however if the plug is in the power conditioner/surge protector but unplugged from the Marshall it stops. So it’s the Marshall. Why would my Marshall make my twin crackle???
     
  2. Jack Harris

    Jack Harris Member

    Messages:
    3
    Joined:
    Jun 17, 2019
    I’m pretty sure it’s this mimiq I’m using in stereo coupled with something else? Is there any reason why a pedal stereo out would make the amp plugged into the mono side crackle? When I take the plug out of the stereo out it stops. I’ve tried a few different cables so it isn’t that. Would a load issue do this? Again I didn’t seem to notice this crackle until I got a one spot iso brick. Why would this happen?
     
  3. xtian

    xtian Member

    Messages:
    1,886
    Joined:
    Dec 15, 2010
    Location:
    NorCal
    You have a LOT of variables, and math says it’s in the pedal board. Start dividing your system in half, testing as you go, until you eliminate the issue. That’s how you can zero in on the culprit.
     
    doctorx likes this.
  4. Vanyu

    Vanyu Member

    Messages:
    366
    Joined:
    Oct 11, 2015
    Location:
    Arkansas
    Sounds like a ground loop to me.

    Are you using your effects loop to drive any of your pedals? I’ve found that out front pedals and fx loop pedals need to be on a separate supply.

    If all of your pedals are out front, then are you using an ungrounded input cable on one of the amps? Using two regular cables creates a ground loop hum. Simply unsolder your ground wire from one of your input cables (and label it so it doesn’t get mixed up with regular cables!). Another option is to use a 3 to 2 prong AC adapter on one of your amps.
     
  5. Jack Harris

    Jack Harris Member

    Messages:
    3
    Joined:
    Jun 17, 2019
    So I redid my board to run mono (one amp as opposed to a double amp stereo rig) and it’s still an issue? I’m wondering if it’s just a scratchy input on a pedal that is being exacerbated by a higher noise floor due to some ground hum or a bad cable. I’ve been trying to avoid testing every single cable/pedal I have, but ya gotta do what ya gotta do I guess.
     
  6. Vanyu

    Vanyu Member

    Messages:
    366
    Joined:
    Oct 11, 2015
    Location:
    Arkansas
    Yep... Gotta love pedal boards! Been there done that one, patch cables can and do go sour, good luck on your hunt and let us know how it goes!
     
  7. BluntForceTrauma

    BluntForceTrauma Member

    Messages:
    3,001
    Joined:
    Jun 6, 2014
    Location:
    Tucson, AZ
    Yep I found this to be true also. My board has 4 pedals in front of the amp and 4 pedals in the loop. Also a Shure wireless receiver. I had annoying hum problems until I started using 3 wall warts to power the board. One Shure wireless 12V to the Shure wireless. One One-Spot to the 4 pedals in front of the amp. One One-Spot to the 4 pedals in the loop. No more hum problems.
     
  8. Glitch Magnet

    Glitch Magnet Supporting Member

    Messages:
    1,647
    Joined:
    Dec 9, 2009
    Location:
    Lower Hudson Valley, New York
    I would never suggest either of the measures you've advised to cure a ground loop issue.

    I would not break the shield on any unbalanced signal cable. To do so means you're relying on the electrical ground for your signal return. Good, consistent, and reliable signal quality relies on the integrity of the entire signal path, which includes both the center conductor and shield. To rely on the electrical ground to carry your signal represents a significant compromise, and defies everything we know about maintaining a proper signal path.

    You can often break the shield connection on a balanced signal because the shield is not part of the signal path. However, for an unbalanced signal, where the shield is an essential part of the signal path, the right way to lift ground is to insert a proper transformer or active equivalent.

    I would never suggest using a ground lift adapter on the AC power cable. That is a safety violation that could have grave consequences. Lifting the ground connection to the main power outlet means, in the case of an electrical fault, high-voltage AC electrical current is going to pass through your pedals, cables, the other amp, and/or your body. Bad idea.
     
    Last edited: Jun 20, 2019
    eolon likes this.
  9. Vanyu

    Vanyu Member

    Messages:
    366
    Joined:
    Oct 11, 2015
    Location:
    Arkansas
    Straight from Strymons website:


    Some things to try when you experience a ground loop are:

    • Plugging both amps into the same circuit or power strip.
    • Lifting the ground on one of the amps. Some amps have a ground lift switch for this.
    • You can also use a prong adapter that eliminates the ground prong for just the second amp.
      • ***Make sure to remove this ground-lift adapter when using the amp by itself. Grounding is important for your safety and that of your equipment.***
    • Cutting the ground/sleeve wire on the cable connecting the last pedal in your chain to the second amp.
    • Getting a ground hum eliminator box between the pedal and one of the amps. Ebtech makes several products for this.
     
  10. pdf64

    pdf64 Member

    Messages:
    5,657
    Joined:
    Aug 9, 2008
    Location:
    Staffordshire, UK.
    Those suggestions indicate either ignorance or a wanton disregard of the basics of electrical safety. It’s extremely unfortunate, appalling really - shame on them :eek:
     
    eolon and Glitch Magnet like this.
  11. Glitch Magnet

    Glitch Magnet Supporting Member

    Messages:
    1,647
    Joined:
    Dec 9, 2009
    Location:
    Lower Hudson Valley, New York
    Interesting. Thanks for showing me that.

    I still disagree with these two approaches for the reasons I stated. And, I think Strymon is endangering its customers by suggesting lifting the safety ground on one amp and relying on that amp to get its ground through the other amp via the signal cables and pedals. That's just not safe. If the amp's chassis becomes energized due to some fault, it needs to be directly grounded so it trips the main circuit breaker rather than passing current through you and your valuable pedals.
     
  12. eolon

    eolon Silver Supporting Member

    Messages:
    447
    Joined:
    Aug 15, 2012
    Location:
    Northwest Ohio
    Glitch Magnet likes this.
  13. eolon

    eolon Silver Supporting Member

    Messages:
    447
    Joined:
    Aug 15, 2012
    Location:
    Northwest Ohio

    Oh, and it has both ground lift and polarity switches on each channel. The signal polarity is important - especially with pedal boards, because some pedals invert the guitar signal and some don't, and usually you can't tell, and the pedal manufacturer doesn't tell you - they assume you are playing through a single amp. But if you play stereo amps (or more) an inverted polarity on one amp compared to the other will make your tone weak and cheesy-sounding. With a polarity switch, it is easy to get both signals in phase again.

    Best Regards,
    Don
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice