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Help needed amplifier, A/B box & ext. preamp

Discussion in 'Amps and Cabs [BG]' started by atoni, Aug 23, 2004.


  1. atoni

    atoni

    Jan 23, 2004
    Helsinki, Finland
    Endorsing Artist: Salo Guitars
    I founded spare A/B box from our guitarist's "junk pile". Can I do the following application?

    bass
    |
    |
    A----->SVT2pro's pre (normal input)--->SVT2pro's power amp----->cabinet
    B----->External JMP-1 preamp-------|

    Signal from bass to A/B box which is used to switch between SVT2pro's own preamp and external preamp. External preamp's output is connected into SVT2pro's power amp in.

    Does the connection from external preamp into SVT2pro's power amp in break the SVT's own preamp path into power amp section.
    External preamp is a guitar preamp to use for distortions and SVT's own preamp section is used for cleans and Ampeg growl.

    Hope you get my point :D
     
  2. I can't say for certain, but on my Peavey plugging anything into the poweramp in socket cuts off the preamp, even if it's just a cable with nothing else on the other end.
     
  3. pedroferreira

    pedroferreira

    Feb 10, 2003
    Portugal
    What he said
     
  4. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    you need a 2nd a/b box to do that, once you plug into the poweramp input the internal preamp is bypassed
     
  5. atoni

    atoni

    Jan 23, 2004
    Helsinki, Finland
    Endorsing Artist: Salo Guitars
    Could you explain how to hook it up with two boxes?

    Could this work with one A/B box which can be used as:
    one input Z to two switchable outputs A/B
    or
    two switchable A/B inputs to one output Z

    1. Bass into SVT's input
    2. SVT's preamp out signal into A of the A/B box
    3. SVT's tuner out signal into JMP-input
    4. JMP-1's output signal into B of the A/B box
    5. A/B box's input/output signal into SVT's poweramp in
     
  6. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    yeah - that works perfect - good job :)
     
  7. atoni

    atoni

    Jan 23, 2004
    Helsinki, Finland
    Endorsing Artist: Salo Guitars
    But does the connection number 5 break the signal from SVT's preamp out jack...?
     
  8. yes but no because the signal is coming from the pre-amp into the a/b and finaly into the pwramp= no break in that chain ;)
     
  9. atoni

    atoni

    Jan 23, 2004
    Helsinki, Finland
    Endorsing Artist: Salo Guitars
    Hmm.. the SVT manual says following about Power Amp In jack:

    "This jack accepts a signal to be sent to the power amp and the Slave Out jack. It does break the path from the Preamp Out jack. This can be used as a post-Master patch point."

    I understood that if I plug something in the Power Amp In jack, there is no signa coming out of Preamp Out jack.

    Well I'm going to try to hook up this monster today or tomorrow, and see what happens. I hope that I don't screw up my amp :)

    Thanks for the help fellow bassists!
     
  10. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Not quite. Check page 3 of manual, where there is a "system block diagram".

    The power amp in jack is AFTER the preamp out. The power amp in jack IS ahown as a "switch type".

    What that means is that when you plug into power amp in, the signal from preamp output is disconnected FROM THE POWER AMP IN. It STILL GOES to the "preamp out" jack.

    So you can use the preamp out and power amp in the same way as you would use a line in/out.

    In your case, you want to use the A/B box, so you can do it as we discussed in PM a few days ago, same as you posted above.

    Have you tried it yet?

    The only thing to remember after that, is that the master will only affect the 2PRO preamp. You have to use the master on the JP-1 to set its level.

    That actually is good, because you will probably want to set them differently anyway. But when you adjust level you will have two knobs to turn.

    For any of these sorts of question, on any unit, it is good to check for a block diagram. That is sort of a "roadmap" of the unit, and will tell you how the signal flows. Then you can see if some hookup idea is workable.
     
  11. atoni

    atoni

    Jan 23, 2004
    Helsinki, Finland
    Endorsing Artist: Salo Guitars
    Ok.
    I'm going to try this today. Thank you all for your help, and all the best for you!