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strange input jack with preamp. can I rewire?

Discussion in 'Luthier's Corner' started by emjazz, May 7, 2005.


  1. emjazz

    emjazz Supporting Member

    Feb 23, 2003
    Boston, MA
    Hi all. I just got a Jim Williams preamp and he uses an input jack that I've never seen before. It ended up finding it at Stew Mac. It's this one: http://www.stewmac.com/shop/Electro...ecial_9-pin_Switching_Stereo_Output_Jack.html

    Well, it doesn't fit into the pre routed shaft that the typical switchcraft jack for my bass fits in. Can I rewire the preamp using the jack that I already have or do I need to do something as drastic as reroute the hole? Thanks.
     
  2. emjazz

    emjazz Supporting Member

    Feb 23, 2003
    Boston, MA
    Here's the schematic:

    I'm not using the alternate power switch.
     
  3. paintandsk8

    paintandsk8 Pushin' my soul through the wire...

    May 12, 2003
    West Lafayette, IN
    You can rewire it using a typical jack, but you will have to use that "alternate power switch". That 9-pin jack is basically a DPDT switch that is "toggled" by the insertion of a 1/4 phone plug. So, basically when you use that jack, when you plug your bass in, it automatically turns your electronics on, and when you unplug it, it automatically turns your electronics off. So, if you want to use a normal jack, you have to wire in that alternate power switch so you can manually turn th electronics on or off.
     
  4. emjazz

    emjazz Supporting Member

    Feb 23, 2003
    Boston, MA
    Will this toggle act as an active/passive switch? Or maybe an on/off switch?

    Is there an input jack that will do the same thing without the switch that is the same size as a standard input jack?

    Thanks so much. This is a big help.
     
  5. paintandsk8

    paintandsk8 Pushin' my soul through the wire...

    May 12, 2003
    West Lafayette, IN
    Whether or not the toggle will act as an active/passive or an on/off depends entirely on the preamp, and this one I am not familiar with.

    You can wire a typical stereo jack as a switch. The problem is that your preamp is using the jack to switch two seperate circuits. A stereo jack can only be used to switch one circuit.

    It is *possible* to make this circuit work with a stereo jack acting as a switch and then using a relay to activate the second circuit, but If I were you, I would just get the toggle, or re-route for the 9 pin jack.
     
  6. emjazz

    emjazz Supporting Member

    Feb 23, 2003
    Boston, MA
    Thanks again. I got the toggle from radio shack and it works fine. I'm just frustrated that it's on a toggle because I don't really want to drill an extra hole in my bass for it. Maybe if I decide to keep the preamp than I'll do it.

    One more question. If I just leave the toggle on will it kill my batteries even when I'm not plugged in?
     
  7. paintandsk8

    paintandsk8 Pushin' my soul through the wire...

    May 12, 2003
    West Lafayette, IN
    That I do not know. I would guess yes, but I don't know enough about the pre to make a definitive answer.
     
  8. gyancey

    gyancey

    Mar 25, 2002
    Austin, TX
    You can't use a normal jack because that preamp is using a biopolar +-9V power supply. One solution is to use a discrete N-channel MOSFET between the negative -9V battery supply and the preamp with the gate tied to -9V via a large value resistor and to the short lug of a standard stereo jack. In other words you're best off using the jack that came with it.