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Need Amp Tech advice please

Discussion in 'Amps and Cabs [BG]' started by Zapp, Sep 23, 2005.

  1. Zapp


    Sep 4, 2005
    Gruene Texas
    Need a tech to look at my logic here and advise:

    This is on an early 90's Workingman's 12. Nothing wrong with the amp but I am trying to modify a switch matrix. The amp has a jack for external cabinet, and that jack is tied to a six-pole three-way switch.
    My objective is to isolate the external Cab jack so that it is ON all the time 24x7. The way SWR wired it, it does what the internal big driver does, so it is impossible to isolate JUST/Only the external cabinet.

    The picture shows the wiring: the external jack is the round thing to the left, and the switch sits right beside it to the right. I marked a few parts with text.

    The three-way switch:
    - Upper position is Horn + Internal 12" Celestion + External jack
    - Middle position: everyone off except headphones
    - Lower position: Leaves out the horn/tweetie. external jack and internal biggie are "On"

    I think what needs doing is the following, but do NOT know what effect this will have on current draw, amperage, etc [will the fuse be affected?]:
    1. Sever both of the external jack's single-core leads from the upper and lower posts of the switch
    2. Leave the red internal-driver lead attached to the remainder of the single-core wire attached to lower post
    3. Route a new insulated strap from the upper left post to the lower left post
    4. Route a new insulated strap from the white power-lead joint at the middle left post of the switch. [NOTE: hard to see, but the middle two posts of the switch are bridged]

    That should do it, I think. Could someone comment on this please?


    Attached Files:

  2. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    Disconnect the external jack wires from the jack.

    Remove said wires from the switch and throw them away leaving the internal speaker leads intact.

    Run two new wires from the external jack to the amp/internal source totally bypassing the switch remembering to keep them in phase.


    Or did I miss your point?

    I would remove the switch from your external cab wiring altogether since it wont be needed. It would eliminate a mechanical component from the path which would otherwise be a potential point of failure.

  3. Funkengrooven

    Funkengrooven Turn it down? You gotta be nuts!!

    Lowtonejoe is correct...If you can use a schematic Email Fender and they will send one. or I can email Fender
    You may also connect it in other ways but I would rather draw it than talk it.
    I'll see If I can score a schematic.

    Workingmans 12 ..ok got it.
  4. Zapp


    Sep 4, 2005
    Gruene Texas
    i do understand the logic but the instructions aren't precise enough for me to get it done.
    See that little red wire that intercepts the lead from the ext jack to the mid-poll of the switch? that is the main power [+] lead to the big internal 12. so its gotta be soldered somewhere if I "throw away" the rest. that's why I was figuring on severing that strap on the jack-side of that point where the Red wire is patched in. why mess with a good solder point.

    The ground to the ext jack is fine as is, so it doesn't need to be messed with. you can't see it in the pic cause its black and skinny and snakes up the left-most edge of that jack and is tacked down at about 11 o'clock. So all that jack needs is to somehow bridge over to either that big white wire or down to the common solder point where the white one is nailed to a capacitor or somesuch [very bottom of the picture, out of the frame of view]. Thing is, I'm not 100% sure I can get to that spot well enough to secure a good connection.

    how will all this affect the draw? any ideas?

  5. Trevorus


    Oct 18, 2002
    Urbana, IL
    Why not take a high quality switchcraft switching jack that (when you plug in a speaker cable) it will cut off the internal speaker. This will then send full power from the amplifier to an external cab. You just need to make sure not to go below the amplifier's rated impedance.
  6. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    Fair enough.

    You should remove (snip off is fine) the wire from the top left of the switch to the jack and from the jack to the red wire. Then you need to attach (solder) a jumper from the red wire back to the top left of the jack so that it is still connected to the top and bottom left terminals.

    If you are fretting about saving solder joints you probably shouldn't be messing with you amp like this. Use an insulated piece of wire.

    So you are saying that the ground on the jack is going to chassis ground, right?

    It would be nice to see exactly what you were talking about but if that is indeed the main wire that is powering the speakers then you can just solder in a jumper from the jack to the wire or splice into it at a convenient location.

    Take a real good look and make sure you can before you start this project.

    Exactly the same as before.

    Disclaimer: All this advice is based on a boatload of assumptions. A schematic would really help. Enter into this project at your own risk.