Running Kemper Powerhead Into My Vibrolux 2x12 Speakers

  • Hi guys, I've seen a lot of posts about speaker cabs, ohms, FRFR speakers etc. But what I"m looking for is an answer to something a little more specific.


    I just got a powerhead, I'm going to be using it 90% for recording. However, I would like to every once in a while to go play with friends or maybe a live performance.


    I noticed on the back of my Fender 68 reissue Vibrolux combo amp, I can unplug the built in head and run something else into the speakers.


    Would this be safe to do? Ive read a lot of conflicting info about ohms and watts.


    I've also read all about how this might not be ideal for the pure sound of the profile, etc. I'm ok with that, as this would be just have the feeling of an amp in the room the few times I do play with people.


    All in all, I'm just trying to avoid buying another cab if I only play with others a handful of times a year.


    I've attached a screenshot of the back of my vibrolux showing the 35 watts and 4 ohms.

  • May I ask, rather than risking an amp malfunction why don't you just unload the Vibro and get a good FRFR or cab that you can use without worry? You could totally use the Vibro but @35 watts as others said, just be careful.

    That's a great suggestion, I am brand new to the Kemper, In fact I just ordered it and it's not even here yet. I will definitely consider unloading the vibro once I spend some time with Kemper.

  • At 4 ohms the 600w amp is a lot!
    What wattage is the speaker in your combo?
    Be careful and you should be OK. Might want to turn the cab off on the Kemper.

    Ya that's what I was concerned with. I looked up the speakers, they are Celestian 30 Tens, which are 30 watts and 8ohms, even though the back of the cab input says 4 ohms. I would definitely be turning the cab sim off after all I've read.

  • Ya that's what I was concerned with. I looked up the speakers, they are Celestian 30 Tens, which are 30 watts and 8ohms, even though the back of the cab input says 4 ohms. I would definitely be turning the cab sim off after all I've read.

    2x 8 ohm speakers wired in parallel = 4 ohms

  • Others have already given you the answer.


    I would simply add that many of the posts about ohms and watts that you have ready online and are causing confusion probably relate to valve (tube) amps.


    The class D power amp in the Kemper is very forgiving of impedance mismatching. In fact the manual says you can leave the power amp on permanently even with no speaker connected. I turn mine off when not in use simply to conserve power etc but I don't believe it is necessary. Try doing that with a valve amp you will have a very expensive repair as you will fry the output transformer.


    Valve amps are susceptible to damage from impedance mismatches where the speaker load is less (lower) than the amp is designed to feed. Basically the amp will keep pushing power unrestricted unless there is a load on it. Think of it like a car engine if you push your foot to the floor in 1st gear. You are likely to exceed the rev limit and blow the engine. However, if you change up gears the engine won't need to rev as hard. The speaker resistance (impedance measured in ohms) acts like the gear box in this example and, as long as the speaker load (impedance) is higher than the recommended amp rating it also acts as a rev limiter to stop the amp blowing up.


    The speaker itself doesn't care what impedance your amp is outputting other than the same wattage at lower impedance means you will be driving it harder so there is more chance of giving it too much power. As long as you keep the volume low enough you should be fine.

  • I’m not aware of any specific way.


    I would start with the Kemper volume totally off and raise it to a level no louder than you are used to with the Fender itself. As you will have the Fender amp with you at the time you could set a room level that sounds good with the Fender (which should be well within limits) then switch over tho the KPA and rais the level gradually until you reach a similar percieved loudness. I would expect you to be safe enough with that. The only thing to be aware of is that double the power isn’t double the volume. It actually takes 10 times the power to double the perceived volume so I wouldn’t want to push 60w of speakers to anything that sounds louder than the Fender itself.

  • I’m not aware of any specific way.


    I would start with the Kemper volume totally off and raise it to a level no louder than you are used to with the Fender itself. As you will have the Fender amp with you at the time you could set a room level that sounds good with the Fender (which should be well within limits) then switch over tho the KPA and rais the level gradually until you reach a similar percieved loudness. I would expect you to be safe enough with that. The only thing to be aware of is that double the power isn’t double the volume. It actually takes 10 times the power to double the perceived volume so I wouldn’t want to push 60w of speakers to anything that sounds louder than the Fender itself.

    Awesome, the fender has always been plenty loud with room to spare, so I don't anticipate needing to go any louder than I have previously. Thanks for the tip!