Can I drive a 2ohm cab safely with my Kemper Power Rack?

  • My backline amp of choice is a 4x10 Fender tweed Bassman reissue. It's 4x10", 8ohm speakers are wired parallel for a 2ohm load. Can I drive this cab at low levels for rehearsing and small club gigs without damaging the power amp in the Power Rack?


    I've read in other threads where driving a 4ohm load is safe although it may cause momentary dropouts.


    Thanks

  • You could try a series parallel speaker splitter box and add a second speaker or dummy load to get it up to over 4 ohms.


    My suggestion would be to rewire the cabinet with a dual input plate where one side gives you the 2ohms needed to run it as is and the other is wired to give you 4 or 8ohms. I did my Mesa Rectifier Horizontal 2x12 with so that When I plug into the left side only I get both speakers connected as normal but whenever a second plug is inserted in the right side it become two independent speakers for stereo use with my 2:ninety power amp.


    I’m not sure whet the exact wiring would be in your case but I’m sure its doable. If in any doubt take it to an amp tech. They will do it in about 5 - 10 mins so shouldn’t be an expensive mod and should be fully reversible if you are worried about preserving resale value e of the cab.

  • My backline amp of choice is a 4x10 Fender tweed Bassman reissue. It's 4x10", 8ohm speakers are wired parallel for a 2ohm load. Can I drive this cab at low levels for rehearsing and small club gigs without damaging the power amp in the Power Rack?


    I've read in other threads where driving a 4ohm load is safe although it may cause momentary dropouts.


    Thanks

    Are you sure, that these four 8 Ohm speakers of this Fender reissue Bassman are currently cabled all parallel to arrive at 2 Ohm overall? I doubt it, because I'm not aware of any tube amplifier, which is able to deal with speaker loads below 4 Ohm. Too close to short cut. I guess, these are two pairs of serial speakers in parallel or two pairs of parallel speakers in series which gets you to 8 Ohm overall.

  • Are you sure, that these four 8 Ohm speakers of this Fender reissue Bassman are currently cabled all parallel to arrive at 2 Ohm overall? I doubt it, because I'm not aware of any tube amplifier, which is able to deal with speaker loads below 4 Ohm. Too close to short cut. I guess, these are two pairs of serial speakers in parallel or two pairs of parallel speakers in series which gets you to 8 Ohm overall.

    Yes, quite sure. It's a Reissue 59' Bassman. Fenders 4x10 and 4x12 amps of the period including the Super revers and the Bassman all ran at below 4 ohms.


    Here's the specs from Fender's site:



    ELECTRONICS

    Voltage 120V

    Wattage 45 Watts into 2 Ohms

    Controls Presence, Middle, Bass, Treble, Volume (Bright Channel), Volume (Normal Channel)

    Channels Two

    Inputs Four - (1/4", Two Bright and Two Normal)



    So what do you think Burkhard? Will my Kemper tolerate a 2 ohm load?

  • Wasn't aware of this 2 Ohm tube amp. Our digital power amp cannot be used below 4 Ohm. I suggest, you modify the cabling of that cab to derive at 8 Ohm. The power amp can handle that perfectly. I don't see any disadvantage.

  • As proposed above the cabling in series/parallel should be no Problem. Btw - as I remember - the cabeling can easily be done without soldering. (the Speaker-Junction is provided with cable-lugs).

  • The Problem is not the power-stage of the profiler (if it is not driven at full volume over a Long period) but the Speakers. They obviously cannot handle the huge power of the profiler. 600 Watt at 8 Ohm would mean 1200 Watt at 2 Ohm

  • The Problem is not the power-stage of the profiler (if it is not driven at full volume over a Long period) but the Speakers. They obviously cannot handle the huge power of the profiler. 600 Watt at 8 Ohm would mean 1200 Watt at 2 Ohm

    No. It would be 1200 watts at 4 ohms and 2400 watts at 2 ohms (if the power amplifier would work at 2 ohms), BUT the power is limited to 600 watts.

  • That's not correct, the powerstage is limited to 600 Watt, when a 8 Ohm load is connected. Due to physic-laws the Output-power increases by square root of 2 when the load is halfened. ;)

  • That's not correct, the powerstage is limited to 600 Watt, when a 8 Ohm load is connected. Due to physic-laws the Output-power increases by square root of 2 when the load is halfened. ;)

    And the rules are ....
    (U = Voltage (Volt), I = Current (Amper), R=Resistor (Ohm),P = Power (Watt)

    1. U = I*R
    2. I= U/R
    3. P= U*I => P = (I*R)*I => I2*R. (For solid-state amp, current intensity goes by square damaging the power transistors)
    4. P= U*I => P = U * (U/R) => U2/R ( For Tube amps, voltage goes by square so audio transformer get's damaged)

    For 600W at 8Ohm you have 8.6 Amper and 69 Volt.
    So don't use a Guitar Cable to connect your Cabinet :)

    Be the force with you ;)