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Magnetic interference from my Sunn 1200s

Discussion in 'Amps and Cabs [BG]' started by Infiltration12, Apr 26, 2010.

  1. Hey guys,

    I was having problems using my Bass Pod Pro with my sunn 1200s, thinking I had a ground loop problem. I tried every trick in the book to fix the ground loop, but I was turned on to the idea of magnetic interference from the Sunn in this thread:

    Is there any way to fix this? I got rid of the Bass Pod and got an Art 351 graphic EQ, but the problem persists. A quick google search told me that there was no way to block the magnetic field, but could I replace the power transformer in the Sunn? How much would that cost?
  2. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Probably more than the amp is worth. EMI decreases as a product of the square of the distance between the source and the receptor, so the easy fix is to separate the components.
  3. I was afraid of that. I have to have the components 4 feet apart to even dull the hum. I love this amp, but I may have to try something else.
  4. Four feet apart is ridiculous. It's not induced hum over that distance. The problem with racking equipment IS induced hum and ground loops as you have discovered. Amps with toroidal power transformers are less likely to induce into associated equipment than transformers with traditional laminations but they are not immune.

    I bolt the power amp directly to the rails but all other items are insulated with "Humfrees". This prevents ground loops via the rack itself. The grounds should be lifted if there is a switch for that provided. If you use a power bar in a rack form place that between the amp and the preamp.

  5. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    +1. Even the worst possible devices where EMI is concerned, magnetic pickups, don't react to power transformers at a range of four feet. Something else is happening.
  6. I glanced at this and read it as 'Magnetic Interference from the Sun'. I was going to post up that my aluminum foil hat (easy to make) takes care of that problem for me, but alas, I had the topic wrong.
  7. I already have Humfrees on all of my gear. My Sunn 1200s doesn't have a ground/lift switch, but the ART 351 has one. I've tried switching it, but didn't get results.

    I don't know what else it could be. Even when the ART is resting atop the rack case and not touching anything made of metal, there still is a buzz. As I move it away from the 1200s, the buzz fades out. I guess I should also mention that the buzz is always there even if I engage the "Tuner Only" switch on my amp, which is supposed to mute all sound coming from the amp.
  8. bump for the morning
  9. Four feet of separation is usually more than enough to kill RF hum.

    I'm wondering if you have a bad cable(s). Sure sounds like a cable/connector/grounding issue to me.
  10. +1, thanks for saving me the typing!!! :)

    OP put all of your rack equipment on the floor separated and unconnected.

    Connect the amp only - do you get the hum?
    If no, connect the tuner to the tuner out and AC. do you get hum?
    If yes, use a ground cheater plug to temporally remove the ground from the tuner. Is the hum still there?
    If no make yourself a cable that is grounded only at the amp end and use that to connect to the tuner. Never use a unit with its mains ground disconnected.

  11. Thanks for all of the help... I'll test everything tonight. I'll be keeping my fingers crossed...
  12. Amp only- no hum

    I don't have a rackmountable tuner, used the ART 351 instead:
    There was hum with the 351 connected, tried switching the ground/lift switch, that didn't help
    Tried using cheater plug, didn't help at all

  13. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Four feet is not necessarily enough, but it usually is....

    So if there is still hum, there is a separate problem.....

    1) describe setup in detail.

    2) did this just start, or has it been a feature of these amps forever?

    3A) Plug in a signal cord same as you have been using to the amp, and use something, paperclip, alligator clip, whatever, to "short" the signal wire to ground. (I assume you have been using an unbalanced input wire....) DO you have hum with that setup?

    3B) now touch the shield connection of the plug (the outside of a standard metal phone plug) to the chassis of some other piece of gear that has a grounded mains cord.... does that change the hum, or cause it?

    if you have hum in case 3A, then the problem may be inside the Sunn unit. Possibly a broken ground wire, etc on the input.

    if case 3A is OK, but case 3B causes hum, then the Sunn unit has a "pin 1 problem", and you need to use the balanced inputs only..... and probably should cut the shield connections at one end of the balanced cable.
  14. Ok, here it goes...
    Music Man Stingray
    Furman PL-Plus(Tested with and without components plugged into the power conditioner, there is no change in hum)
    Art 351 Graphic EQ
    Sunn 1200s
    Schroeder 410

    Signal path: bass-Sunn input-Sunn FX loop send-ART input-Art output-Sunn FX return-speaker out-Schroeder.

    This problem has been present whenever another component is in the signal path with the 1200s. These components will function with no problems with my GK 400RB.

    Could you tell me exactly how to "short the signal wire to ground"? I'm not sure what you mean.
  15. Final bump
  16. jastacey

    jastacey Supporting Member

    Feb 8, 2009
    I have the Bassman 1200, which is an updated version of the Sunn 1200s .... did you try using the amp with out any pedals route through the FX loop?
  17. Andyman001

    Andyman001 moderation must be taken with a grain of salt

    Feb 11, 2010
  18. Andyman001

    Andyman001 moderation must be taken with a grain of salt

    Feb 11, 2010
    Just for sh*ts & giggles, try running through the EQ then into Sunn input to see if problem is in FX loop circuit.
  19. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    I mean to have a cord plugged into the Sunn, with no signal, basically, without the free end being left "open" (that usually hums)..... BUT NOT plugged into anything that has a line cord....

    So assuming you are indeed using regular signal and shield (unbalanced) cords, you could probably plug in the bass, and turn down the volume.

    If it hums, there is likely some internal issue in the Sunn that may be fixable.

    The second test is if you get NO hum with the first one...... and it is to have one of the things that it hums with, maybe the ART EQ, powered up just as it is when the system hums, but with no cords in the ART. Touch the SHIELD connection of the cord from the Sunn (usually the metal plug handle) to some bare metal on the ART.
    That means there is NO signal connection, you are ONLY connecting the input ground of the Sunn to ground on the other unit..... There SHOULD be no hum, but there might be.....

    if THAT produces hum, the Sunn has a "pin one" or ground problem and is probably nailed as the source of the humming.... and it is possibly in the design of the amp, harder to fix, but a very good tech could do maybe it.
  20. Just thought I would check in again, I tried the tests suggested, and there is only hum when the units are within 3 feet of each other. However, there is a "sweet spot" when the ART is at the top of my rack case, where the hum is significantly quieter, but still present. So that's the configuration I'm running right now.

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