A/b/y Pedals: Switching Channels On A Jcm800 2204

Discussion in 'Marshall Amps' started by InfernoChicken, Apr 10, 2019.

?

Possible?

  1. Yes

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  2. No

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  1. InfernoChicken

    InfernoChicken New Member

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    So I built a sweet JCM800 2204 last year and it is the sound I was always looking for!!

    Both channels sound great, but for me, as for many others, the HIGH input is the way to go. But if you need a real clean tone, I mean really clean, by not only rolling down the Volume Knob on your guitar, the LOW input seems to get interesting. Logically, I come to the conclusion that channel switching via an A/B/Y pedal should do the trick.

    Now I have read some posts about people who claim that this would not work, as the LOW channel overrides the HIGH channel, so if you connect cables to both HIGH and LOW jacks to the A/B/Y pedal, only the LOW channel would work.

    My question here is about the functionality of A/B/Y pedals: Considering that both channels are connected to the switching pedal; if one of the channels is selected, shouldn't be the other channel "unselected" meaning "disconnected"? And in this case, the *not-active-channel-cable* just be an extension of the input jack pins (ground and hot) ??

    If my assumption is correct, then there sould not be an issue with switching as there is no cable/input registered by the amp?

    TL;DR: Are A/B/Y pedals cutting the input signal physically by just not connecting the guitar output circuit or are they only muting the not-active guitar output (Scenario: 1 Guitar ---> HIGH/LOW channel JCM800 2204) ?
     
  2. pedecamp

    pedecamp Well-Known Member

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    It wont work without doing some mods to the amp, when you plug into an input it disables the other input. The other issue is the shared volume and preamp, even if you modded the amp so you can be plugged into both inputs at the same time the volume between the high and low input is so far off it will never match. Get yourself a 2205 or 2210.
     
  3. InfernoChicken

    InfernoChicken New Member

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    Thanks for your answer. But where does the amp decide whether there is something connected to the low channel? If for example you just plug a cable into the low channel, without guitar, the amp should not detect aynthing as the circuit isnt closed, right? So if the pedal does not close this circuit as well, why wouldnt it work?

    About the channel volume: there are clean boosters to fix that.
     
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  4. Len

    Len Well-Known Member

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    The jack you plug into has a physical switch in it. If a cable is plugged in the amp knows...
     
  5. InfernoChicken

    InfernoChicken New Member

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    A physical switch inside the amp? I built the amp according to the 1987 schematic, and I havent seen nor have I built a switch into it.

    So there is no jack-detecting mechanism inside here.
    I have expanded the tags of my thread, maybe some electro nerd could clear out what i am missing :)
     

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  6. Marshallhead

    Marshallhead Well-Known Member

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    Assuming you built the cascading gain type circuit, look closely at the low input jack socket, and in particular what happens when you plug a cable into the socket. That’s where the ‘switching’ is happening.

    Basically you are tapping into the circuit further down the signal chain, cutting the first gain stage out.
     
    Jethro Rocker and InfernoChicken like this.
  7. ampmadscientist

    ampmadscientist Well-Known Member

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    There is only 1 preamp.
    The switching is accomplished by a switching contact inside the LOW jack.
    When you plug into the HI input, the switching contact in the low jack is engaged.
    When you plug into the LO input, the switch contact disengages.

    To make A/B/Y, there needs to be 2 separate preamp stages and 2 sets of volume controls, etc.
    This amp does not have that.
    But if you have a second external preamp, and you have an effects loop installed, you could do that with an ABY switcher.
     
    InfernoChicken likes this.
  8. InfernoChicken

    InfernoChicken New Member

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    Ahhh now I understand! Thanks a lot mates! I love this forum.:cheers:
     
    Mitchell Pearrow likes this.
  9. ampmadscientist

    ampmadscientist Well-Known Member

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    Are you in OZ?

    Yes that is correct: this is the best guitar amp forum. :rock:
     

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