Is there a fix yet for the MT15 noise/hum?

Discussion in 'Amplifiers' started by jisham, Aug 7, 2018.

  1. desertdweller

    desertdweller New Member

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    Bump!

    Long time Mesa player, I received my first PRS amp today, the MT15, and I'm having the hum issue. For mine, it's not a tube, it's the effects loop.

    When you plug a guitar into the input with nothing in the effects loop, the amp performs perfectly. The clean channel has zero noise. However even putting a patch cable in the effects loop elicits 60Hz hum immediately. Running anything in the loop, pedals, rack effects, other preamps, or just a cable = 60 Hz hum.

    It's not a tube or the transformer, otherwise it would be making the noise with nothing in the loop. So is there a fix for this? The amp sounds amazing and this is a fix that would make the amp nearly perfect.
     
  2. elvis

    elvis Hamfisted String Banger

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    There is a very good chance that ther FX loop tube is bypassed when there is nothing in the loop. Try swapping V6, that is the FX loop tube.
     
  3. desertdweller

    desertdweller New Member

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    That is a very good ideal. Let me give that a shot.
     
  4. desertdweller

    desertdweller New Member

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    Just tried it, swapped out V6 for another 12ax7 I had here in the house, and it didn't fix the issue. So it's not tubes. I'm wondering if it's a bad ground in the effects loop or if there's an internal part causing interference.
     
  5. elvis

    elvis Hamfisted String Banger

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    The patch cable from FX send to return probably rules out external sources. It's possible that there is a loose ground connection in the FX loop circuit, I had that happen on two amps. But it seems consistent with the other amp owners' experience.

    Best to contact PRS directly.
     
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  6. Bill SAS 513

    Bill SAS 513 Just another old guy in a T-shirt

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    Miscellaneous response, about other, but similar things...A couple people mentioned placing pads between the heads and cabinets, and Les' pucks, which look pretty cool.
    I have been folding up a Yoga mat (about $5.00 at the general store "5 Below") to put between my bass heads and cabs. But mostly due to limited space in my dungeon.

    If you have room, most of what I've read states its better to keep heads off of their cabinets, as to minimize the vibrations, as Tubes can be very sensitive, especially when warmed up.

    PRS has always been good about fixing issues, so I assume they will be doing something to correct the ongoing MT-15 issues.
     
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  7. desertdweller

    desertdweller New Member

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    SO here's an oddity. When I use the FX loop on the MT15 with a speaker cabinet, I get the 60 Hz hum immediately, however when I run the output to a Torpedo Captor and into my PC, no hum from the FX loop.

    I'm stumped. I guess it's awesome for recording and would be fine at a gig, but lower moderate volume playing gets the hum.
     
  8. elvis

    elvis Hamfisted String Banger

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    That IS weird
     
  9. Joe Martin

    Joe Martin New Member

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    I use an ISP Decimator II GString to help reduce the hum noise, which is effective but chokes the sustain a little. My lipl send and return runs through it as well as direct to the front input. Hope this info helps some.
     
  10. elvis

    elvis Hamfisted String Banger

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    TC Sentry. It's unlikely you'll see more work on the MT in my opinion.
     
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  11. Joe Martin

    Joe Martin New Member

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    so I tried a preamp tube swap out as suggested in the forums and put a mullard at7 in the pi position and a Jan GE 5751 in the V3 position. the only change was a reduction in gain not a reduction in the hum noise, which I find is more prevalent when I am connected to the effects loop. thinking of trying the Jan GE in v6 position. thoughts?
     

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