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Dual concentric gain and master pots???

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Terry McInturff, Jan 3, 2018.

  1. Terry McInturff

    Terry McInturff 40th Anniversary of guitar building! Gold Supporting Member

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    To the amp gurus...

    Given a simple-ish amp such as a Marshall 2204, would it be that hard to use dual concentric pots on the gain and master, in order to set-up two different gain/master settings...and then footswitch between them via a relay or such? In effect, creating a "two channel" amp (with shared EQ)?
     
  2. Jeff Gehring

    Jeff Gehring Silver Supporting Member

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    The biggest trick is to avoid switching pops that would occur when changing channels. Also there would be a change in the loading/voltage division, since you would be paralleling the two existing pots with two more.
     
  3. jay42

    jay42 Member

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    Problematically, 1M dual concentric pots are hard to come by. 500K is the Jazz bass part, so those are easy enough.
     
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  4. Terry McInturff

    Terry McInturff 40th Anniversary of guitar building! Gold Supporting Member

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    http://www.potentiometers.com
     
  5. walterw

    walterw Gold Supporting Member

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    not a dual gain, but it's fairly easy to rig up a switching master volume boost on a knob, i did it myself many years ago on my '78 2203 and it made the amp so much more giggable.

    the idea is to insert resistance between the master volume's ground lug and ground, that makes the master volume not as effective and the amp gets louder. make that resistance the two lugs of a 500k audio pot and you now have an adjustable solo boost knob.

    my setup uses a relay powered by 9V, which i just send via a footswitch on my pedalboard. mine was a little complicated in that i switched in both lugs of the pot between the master's ground lug and ground, and i had to make little jumpers across the legs of the DPDT relay so that while it was switching i didn't have that instant of no connection and the amp on "10"!

    i since discovered a schematic for a far simpler way, where the lugs of the boost volume stay connected between the master volume's ground lug and ground and a simple 2-way relay either shorts across them or doesn't.

    [​IMG]

    either way the master boost is awesome! it lets me run the amp nice and crunchy and still bump my volume for solos that jump out of the mix, and i can get a decent loud clean sound by bumping the volume and turning my guitar down.
     

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