Ampeg SJ 12 T speaker connection

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Gumby, Nov 24, 2005.

  1. Gumby

    Gumby Member

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    I have an ampeg SJ-12t and a THD Univalve. The speaker in the ampeg is hard wired to the amp, but the speaker itself has four tabs for connection. 2 (+) and 2 (-). With the power off on the ampeg, could I connect the the speaker output of the Univalve to the remaining two tabs of the ampeg speaker. I was wondering if there would be any harm to the ampeg if I left the connection on during use of the ampeg, of course the two amps would not be used simultainiously- one or the other. Good idea or bad? Thanks in advance.
     
  2. Wakarusa

    Wakarusa Member

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    Bad idea.

    In your scheme the OT secondary of the Ampeg is still connected and in parallel with your Univox.
     
  3. Gumby

    Gumby Member

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    what difference does it make if the ampeg is turned off? What do you mean the output transformer secondary??? wired in parallel?? What the heck are you talking about? I don't understand your reply, please elaborate. I have a univale amp, not a univox effect. Can anyone else clear this up for me? Let me reiterate, I would like to use my 1x12 ampeg combo as a extra speaker cab. While doing so, the power is off on the combo. The combo does not have a 1/4 inch plug disconnect for the speaker, but the speaker itself does have two open terminals 1 positive 1 negative (4 total). Can I connect to the two open terminals? Is that more clear? Thanks.
     
  4. aleclee

    aleclee TGP Tech Wrangler Staff Member

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    Hooking up two amps to the single speaker is bad news, regardless of whether they're run at the same time.

    You'll be running signal into the second amp and that could damage things in one or both amps.
     
  5. Wakarusa

    Wakarusa Member

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    Your question was perfectly clear the first time. My answer, unfortunately, was not.

    There are two side-effects of doing this that come immediately to mind:

    First, the second amp will see the Ampeg as a load in parallel with the speaker. I'd have to do some math & modelling to figure out the exact effect, but my gut tells me the second amp won't like it.

    Second, the OT in the Ampeg works both ways -- in normal operation it transforms the high voltage (and impedance) of the output tubes into the low voltage (and impedance) of the speaker. Driven as you suggest, it will happily transform the low voltage output of the second amp into high voltages in the Ampeg, but the Ampeg in this case is "off" -- so it's missing interesting features like a bias supply voltage in the power section. You could easily damage the Ampeg's power section by doing this.

    Hopefully that answers the question more completely.
     
  6. Gumby

    Gumby Member

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    Yes, I understand now. Thanks to both of you for the reply. The univalve has a built in dummy load, but the ampegs power section does not, and it is still in the signal path, even though its turned off. No problem.
     

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