Question for JTM45/100 owners regarding background noise/hum/buzz

Discussion in 'Marshall Amps' started by frankcastle, Feb 27, 2016.

  1. frankcastle

    frankcastle New Member

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    Hello!

    So up to this point I have only owned what I considered to be "good for the price" amps (e.g. Peavey 6505+, Mesa Boogie Stiletto Deuce II, Jet City JCA50).

    I saved up and bought something called the Unholy Trinity a Metro/Merren/Friedman modified JTM 45/100. I've always loved music from the 70s and 80s so really a Marshall of some sort really seems like a good fit for me.

    Now the amp sounds great (there are 3 videos that someone has uploaded on youtube if you are curious). But at first I didn't notice it that much but it's like when you notice a scratch in a new car.

    The amp seems to emit a constant hum/buzz through the speakers. I was using a LP copy guitar, I swapped cables, unplugged all pedals, plugged directly to the wall, checked for loose tubes. But the noise persists.

    So my question is this from my understanding amps with a master volume mod, plus extra gain tend to create more noise.

    Is what I am hearing just par for the course?
     
  2. ampmadscientist

    ampmadscientist Well-Known Member

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    With no guitar plugged in...
    This is a buzzing noise, which goes away when the volume is turned to zero?
    Gets louder as (both) volume(s) is turned up?

    Unplug middle preamp tube, turn up volume, buzzing should stop?

    If Yes, This is filament noise in the preamp.
    And yes, there is ways to eliminate the buzzing.
     
  3. frankcastle

    frankcastle New Member

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    Thank you very much for the reply.

    Last night I took out all the tubes, cleaning a bit of white grit of a few pins.
    Move the amp away from an electrical outlet and a bunch of 1/2 inch steel rods (a table I built).
    Left the back cover of the amp off..... can't be certain but when I dropped the cover on the floor I think there was a tiny allen key stuck to the plastic grill on the back of the amp.

    Anyways, not sure which of these things cause it but the noise dropped significantly. Before it was louder and more noticeable than any amp I had every tried (only sample size of 5), but not it is much quieter.

    Before it was a loud buzz, not it is more of a low hum..... which drops to a very quiet hum if I touch a metal part of my guitar.

    I think this might be a grounding issue...... any way to id where it comes from?

    Edit: last night when I did all of this it was at extremely low volumes as I didn't want to wake my wife.

    At low volumes the noise is not that noticeable but as you increase the master volume it does get louder and more severe.

    I will have to give what you suggested about the second pre amp tube a try.

    I will also have to check and see how the different knobs affect the hum.

    On a side note in addition to touching the guitar. Touching the top of the aluminum chasis also cuts a bit of the hum. Does that mean something inside the amp is not grounded properly? Like I said this thing was shipped from New Mexico to Toronto Canada in the winter and even though it was packed as well as possible I bet the postal people were not gentle with the box.
     
  4. shane159

    shane159 Member

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    It is very possibly the wiring in your house. When I bring my amps home from our rehearsal room and plug them in at home, they always are notably noisier. Also, try turning your guitar volume all the way down and see if it reduces the hum. It could also just be your guitar. It sounds to me like your home wiring though.
     
  5. frankcastle

    frankcastle New Member

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    I'll have to check the volume knob on the guitar. I had used it primarily to push the signal for more gain/break up but wasn't paying attention to how the hum.buzz changed.

    If it is the wiring of the house does a power conditioner or some such help to mitigate it?
     
  6. bad565ss

    bad565ss Well-Known Member

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    It could be that your guitar is not well grounded. I dealt with this when I had a tech rewire a Les Paul. Through his little combo workbench amp it sounded fine. Take it home and plug in to my JMP, loud hum,buzz. Take it back to him.
    Same result. I found the problem to be a poorly grounded toggle switch.
    I rewired the guitar myself with shielded wiring and problem gone.
     
  7. Hippy07

    Hippy07 Member

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    Hey frank I'm having very similar problems to you with a 78 jmp 1959. I've taken the amp to a well respected amp tech he agreed that the amp seemed overly noisey. He checked my guitar and the ground was good. I've conveyed to him some suggestions given to me from some helpful forum members. When I get the amp back in a few weeks I will let you know what problems he found and the solutions ( hopefully).
     

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