El34 50/50 Power Amp Connection Help

Discussion in 'Marshall Amps' started by JohnEjackplug, May 23, 2017.

  1. JohnEjackplug

    JohnEjackplug New Member

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    Hello......

    I'm using a JMP-1 and 50/50 Power amp, I run the amp just through channel B at the moment with channel A switched off, I know using channell A in parallel mono mode i have to have speakers attached to both amps but can I run into Channel A on its own if I turn channel B off ?

    Im thinking if Channel B goes bad during a gig can i switch it off and then use Channel A on its own (as long as I turn Channel B off) Not sure if this makes sense lol

    Any help would be appreciated

    Cheers
     
  2. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    :welcome:to the forum...
    yes...
    yes & yes...

    :cheers:
     
  3. DonaldBort

    DonaldBort Member

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    Wouldn't it all depend on what actually goes out in the PA? If the component that fails effects both channels then the answer would be no; however you need to look at the schematics to see if there are independent power supplies for each channel, are the pre-amp tubes shared or is it 1-ECC83 and 2-el-34's per side?
    I used a Rocktron Velocity 300 for a short stint, I ran it bridged and when one channel went out it drastically affected the other (again in Bridged mode) went I switched to stereo and used the remaining good channel, it sounded really thin, not as dynamic and less responsiveness to control settings (volume, definition, reactance). However this was a solid state power amp.
     
  4. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    The EL34 dual monobloc amps are just what "monobloc" implies. 2 distinctly individual/independent amplifiers. The only thing shared is the power cord coming in. Everything from that point on is split separate & they share no stages, or transformers.

    Oh, the case is shared...
     
  5. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    Here, I grabbed this from the owner's manual & put a line through the middle (top to bottom), showing the distinct seperate amps & how they are designed...

    [​IMG]
     
  6. DonaldBort

    DonaldBort Member

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    So the power transformer is shared? If this goes out?
     
    Last edited: May 23, 2017
  7. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    no, there are 2 power transformers - 1 for each side. Each side is a fully independent amplifier...
     
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  8. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    Here's an actual image of the unit:

    [​IMG]
     
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  9. DonaldBort

    DonaldBort Member

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    Okay...Just giving some options for this member to look at to consider and to see how their equipment works, and adding my experience. That's all.
     
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  10. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    yeah, the only thing that makes his question somewhat confusing to some people is that Channel A's input jack has a bridge to Channel B. Channel B, input jack has a disconnect switch. So, if you simply plug into Channel A, you have a parallel bridge from A to B. If you hook into Channel B, it disconnects the bridge, so you can run B independent.

    Either way though, if A & B are bridged, if the power to B is off, you will only be running Channel A, if you are plugged in (Channel A) & the amp is bridged.

    Best bet though, is to run Channel B, if you are planning on only running ½ of the amp.

    Tube amp's can not be bridged, like a stereo solid state amp. The amps still run independent, other than the bridge the signal before the 1st stage of either amp's input...

    Solid state amp's that are stereo, are not dual monobloc, for the most part & have a way of internally bridging, but, it also changes the impedance requirements.

    I think I've got that all right... :)...
     
  11. DonaldBort

    DonaldBort Member

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    I learned something new... One thing i got right is to steer away from the Velocity 300 (I actually went through 2 of them, same issue on each).
     
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  12. JohnEjackplug

    JohnEjackplug New Member

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    Thank you ALL for your input above it is much appreciated !!
     
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  13. JohnEjackplug

    JohnEjackplug New Member

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    I got this from Marshall today after asking the same question...

    Hello John,

    Thank you for your e-mail regarding your question, as long as you switch channel B off this should cause no damage.

    Kind Regards
    Joanna

    Joanna Green | Customer Relations Manager
    Marshall Amplification Plc
    Tel: +44 (0) 1908375411
     
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  14. Sir Don

    Sir Don Well-Known Member

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    Just curious, what about the first stereo power amps that Marshall made? I've got a 9005 model, as I understand it there are some shared components within whereas the dual monobloc is totally separate?
     

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