Please Explain: Power Amp Signal Parallel with Monitor Output

  • The documentation says that the power amp output is internally parallelled to the Monitor Output, presumably so that one could set up a stereo pair of guitar / FRFR cabs with the appropriate output settings.

    I note that when using a powered stage monitor off the Monitor Output, turning off the internal power amp results in a large drop in output volume from the Monitor Output. This can be compensated for by just increasing the volume on the powered stage monitor (or by increasing the volume of the Monitor Output in the Output section, presumably, although I have not tried it).

    All this confuses me a little as the documentation has a very strict warning about not connecting powered devices to the Speaker Output jack, but the Monitor Output jack doesn't care. I guess they're buffered differently...?

    I don't need to keep the power amp on as I'm not using a guitar cab, so other than the resultant power drop at the Monitor Output, is there anything else I need to attend to for my powered stage monitor?


  • The paralleled path is NOT intended to sun stereo from Speaker out and Monitor out. Quite the opposite. Basically what the manual is saying is that both outputs get the same signal at all times. However, one sends upto 600w of power down the cable to drive a speaker the other sends a line level signal to feed an amplifier. If you send 600w into the amplifier section on the powered FRFR you will fry the amp.

  • Yep, as Elvis says, that seems strange.

    I’m not an electral or electronics engineer so this is just a layman thinking out loud; I wonder if it could be becase the two signals a literally just split at the point of sending to the power amp. If the signal pths aren’t isolated somehow then the could affect each other. A good example of this is tryng to run two sets of headphones from a single output. If you use a dedicated headphone amp everything is fine but if you just plug both into a little Y splitter the output level drops significantly as the load the output is trying to drive has been increased. However, in you case I would have expected the Monitor signal to get louder when turning off the power amp.

    However, I would open a support ticket in case there is a hardware issue.

  • Wheresthedug: Yes, that's what I'm thinking as well.

    I don't see it as a hardware issue (yet) because I'm not sure if it's normal or not. At any rate it's not causing me any problems.

    Elvis: I will check power amp boost; that makes sense and I appreciate the suggestion.

  • I just did a little experimenting.

    The Monitor Output level is indeed dependent on the power amp boost level (Elvis wins the free beer!), and whether or not the power amp is turned on.

    The factory default (on my unit at least) for power amp boost is +6 dB. With the power amp ON, turning the boost level up and down affects the Monitor Output accordingly. With the power amp ON and the boost level set to 0 dB, the Monitor Output level is the same as if the power amp is OFF.

    My powered stage monitor, running off the Monitor Output, has plenty of juice to rip my head off even with the power amp off.

    From a design or end-use point of view, I'm puzzled as to why Kemper linked these two outputs - or, rather, made the Monitor Output level dependent on the power amp boost level and ON/OFF state.

    The documentation clearly states that these two signals are linked internally. From the 5.5 Main Manual, page 77:

    "The most common purpose of the built-in power amp of the models PowerHead and PowerRack is to drive a guitar cabinet, therefore it is cabled internally to the MONITOR OUTPUT. However, the MONITOR OUTPUT jack carries the exact same signal in parallel, so you can still use the MONITOR OUTPUT as if the power amp wasn't there."

    Well, OK. :/

  • Yes, I've just carried out the same test and mine does indeed behave exactly as you describe. I can understand how it is working but, like you can't see the logic in linking the monitor out to the power amp boost parameter which isn't even visible if the power amp is turned off.

    At least we know what is going on now. Self help group of the day :-)