Using a Fender ext jack for alternate impedance

Discussion in 'Shock Brother's DIY Amps' started by Prophetsnake, Dec 3, 2019 at 7:05 AM.

  1. Prophetsnake

    Prophetsnake Tele-Meister

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    I'm not seeing any real use for the ext jack on my Tremolux. I just got a new OT for it and it has a 4 ohm tap, so I'm thinking of adapting the ext jack for 4 ohms.
    I figure I would have to split them completely, that is each would have a connection to the common - which I could jump from one to the other - and each a separate tap, and that's it. No shorting jacks, no switches, etc.
    In other words, either unused jack would have to be open.

    Am I right?
     
  2. radiocaster

    radiocaster Poster Extraordinaire

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    Yes, you would be able to use only one jack at a time, which is no big deal since many cabs have 2 jacks for parallel connection anyway.

    Some people use that hole for a mids or master volume control.
     
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  3. Prophetsnake

    Prophetsnake Tele-Meister

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    Thank you!
    I actually have plans for a MV as well, but the best place for that, right in between the output tubes, is occupied by the power switch. I'm going to move that to the now vacant ground position, so not a lot on the panel is going to be labeled correctly.
     
  4. sds1

    sds1 Tele-Afflicted

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    Yeah exactly, and you lose that protection in case no speaker load is present, but there's no other way to do it in this case.
     
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  5. Bill Moore

    Bill Moore Tele-Afflicted

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    On my DR build, I kept the main speaker shorting jack, and ran the 4 and 8 ohm leads to a switching jack in the aux hole. Default is 8 ohm, when a plug is in the aux hole it is switched to 4 ohm. I expect to only use 8 ohm speakers, but if I wanted to, a dummy plug inserted into the aux would make the shorting jack 4 ohm.
     
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  6. RottenTheCat

    RottenTheCat Tele-Holic

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    Bad practice. Much safer for one shorting jack and put SPDT switch in Ext jack opening.
     
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  7. Snfoilhat

    Snfoilhat Tele-Afflicted

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    Screenshot from 2017-07-13 10-35-01.png

    Fender used this switching jack on some non-vintage models (I think this is the same that Bill Moore mentioned).

    Dr. Z has used the totally separated secondaries with no shunt to ground -- it's left to the operator to always ensure one and only one load is plugged in (same as discussed at the top of the thread).

    Marshall has used an impedance selector switch.

    All options seem to have trade-offs and possible pitfalls, user error, part failure.
     
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  8. Tube Life

    Tube Life TDPRI Member

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    I purchased the Hoffman speaker impedance switch but it’s pretty big for a Fender chassis and didn’t end up using it. What’s another alternative to be able to utilize all three taps, 2, 4 and 8 one at a time of course and still have fail safe protection? I have an ab763 MojoTone super reverb and I have various cabs etc. primarily would be 2 ohm but occasionally 4 and 8 also. Thx.
     
  9. Bill Moore

    Bill Moore Tele-Afflicted

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    My Twin build, I used a Marshall switch, and although the hole is large, it doesn't extend too deep into the chassis. In that build I had 4-8-16 ohm taps, and I also incorporated a "series" jack.

    Twin.jpg Twin23.jpg
     
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  10. schmee

    schmee Poster Extraordinaire

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    [​IMG]
     
  11. Wyatt

    Wyatt Tele-Afflicted

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    That's what I used in my Vibroclone. But since it retains the shunt to ground, it's not real useful for an either/or impedance, but it great for keeping the impedance matched when using an ext cab with a combo.
     
    Last edited: Dec 3, 2019 at 3:12 PM
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  12. FenderLover

    FenderLover Friend of Leo's

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    I'll add my Matchless to the list. Not saying it's a good idea, but others do it too, and so have I.
     
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  13. radiocaster

    radiocaster Poster Extraordinaire

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    That seems totally pointless, you have 3 holes, you can use one for the 4 ohm out as well.

    Marshalls have only 2 holes, but a 3 way switch to select impedance. Now that is more versatile.

    And anyway, the switch is to be avoided if possible, because it can lead to more mistakes if setting up fast and you don't look at the switch because you expect it to be in the "usual" place. I am saying this in particular to the one in the diagram. Plus most people don't use two 32 ohm speaker cabs to warrant two jacks in parallel to be used with the 16 ohm setting.
     
    Last edited: Dec 4, 2019 at 1:04 PM
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  14. schmee

    schmee Poster Extraordinaire

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    It's just a common example of using the switch, use it with any impedance tap you want and one jack if you want.

    "if setting up fast and you don't look at the switch because you expect it to be in the "usual" place" Ditto for leaving the plug in the wrong jack. No different.
     
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  15. Prophetsnake

    Prophetsnake Tele-Meister

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    Hmmm. Something to think about anyhow. At the moment, I can't see myself using anything but the 8ohm option, so I may just leave it as stock and park the 4 ohm lead until I change my mind. It wouldn't take a lot to wire it up some other way, so I think I'll just leave well enough alone.

    Thank you, gents!
     
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