Need urgent help: Powered Kemper on real cab, all of a sudden shitty 'crackling bypass'-sound (details in post)

    Ok,

    I'm am confused and clueless. I hope someone can help me with this as this happened to me twice now.
    I'll explain in detail. In all cases I used the internal poweramp on a real cab in primarily in Performance Mode (when in trouble I tried other rigs using Browser Mode, but that made no difference for the issue I came across). Monitor CAB is set to off.

    After 5 years of using my Kemper without any issues I was auditioning at an experienced band I'd like to join.
    I'm using the poweramp in my Kemper on a 4x12 cab (unknown brand but sounds good). I turn up the volume (not crazy loud but really loud without the need of hearing protection).
    Then after the rest of the band joined after 10mins or so the sound when completely shitty. It's hard to describe but I would describe it as if you would bypass a guitar pedal, so just the sound coming from just the guitar, the volume was a bit lower and sounded crackled. The screen on the Kemper Remote and the Kemper itself looked ok. I switched off the Kemper, turned it on again and it improved but still way from as it should be. I managed through the rehearsal and luckily they could see through and judged my playing not my sound.

    So two day's layer I rented a rehearsal room in my hometown to dive into this issue. I got a Marshall 1960 4x12 , connected my Kemper (again using it's internal poweramp), put in my earplugs and play loud, really loud (even with plugs in) for two hour without any issue! All presets were there sounded great. No problems at all. So my conclusion: it must have been the CAB or speaker cable at the auditioning. Just to be sure I did a factory reset and restored my latest backup. Still the same proper results.

    Then the day before yesterday I went with my other band (they play even louder), got my Kemper to their rehearsal room (at another town), again a 1960 4x12. Very loud playing for 3 hours without any issues at all! So felt confident with my Kemper.

    Yesterday I got my second rehearsal with the band I auditioned for (feeling confident about my Kemper). Now here is where the story gets really weird.
    I arrived 30mins early so I could take time to settle my sound. I got the same CAB as the first time that gave me trouble. But this time it sounded great! Volume was 'very loud without the need of ear protection) so I took the time to configure the EQ on the MONITOR OUT menu in the OUTPUT MENU to my needs on that specific cab. I even turned up the volume to even louder. Then when I was satisfied with the settings I pushed the STORE button three times to save the performce.
    As soon as I pushed the button, THE SAME PROBLEM as the first rehearsal occured. The 'crackling bypass sound at low volume' was there again. I still could change presets and rigs, but they all sounded about the same ('crackling bypass sound at low volume'). Then a technician (experienced repair professional of recording gear and tube amps) assisted me and these were the steps I did to try to solve the issue:

    • Tried a different cable from the Kemper to the cab -> same problem.
    • Tried a different cab -> same problem.
    • Tried a different amp (completely take out the Kemper from the signal chain) -> problem was gone.
    • Replaced the different amp with the Kemper again but this time replace my wireless (Shure GLXD4) with a cable -> same problem
    • Then I restored a backup from USB I created the night before (so the only difference between the backup and current settings where the EQ adjustments I did in the MONITOR OUT section just minutes before). -> same problem
    • We even switched guitars -> then all of a sudden the sound was good again. So the technician said my guitar was the problem (I'm sure it wasn't!! New battery, used the guitar the night before with the other band and besides that the problem started when I pushed the save button on the Kemper, has nothing to do with the guitar).
    • So reconnected the whole setup as it should be (my guitar, my wireless, into the Kemper, on the CAB from the rehearing room) -> no problem at all and I could play the whole night without any issues! WTF??
    • I wasn't able to test any of the other outputs (mains/FOH) but I guess that still worked fine (is use that on a daily basis).

    So I am confused, not a bit, but completely confused.
    I took the time to explain in details what happened because I need a solution for this as I can't afford to have the same experience the third rehearsal in a few weeks.
    The weird thing is that I only experienced this on the same CAB in that same rehearsal room (and therefore with the same band). But if you read through the steps we took above, the problem cannot be the CAB. I couldn't sleep because this issue bugged me as this is a vague issue which I can't explain.

    I read through the Kemper manual and the only reference I could find that could be describing my experience (although I'm not sure if that is really the issue I had) is written in the 'Power Amplifier' chapter in the Basics manual where it says on page 24 'if you are running at high volumes and notice any indications of speaker distress, turn down “Monitor Volume” or “Power Amp Boost”.'
    Not sure where my Monitor Volume where at when the problem occurred but my Power Amp Boost is on 6.0db.

    OS version: 8.7.15.42312 (Jan 30 2013 16:11:29)

    I hope this explanation in detail gives you a proper description of the problem and maybe someone of you had this issue too.
    Or maybe someone from the Kemper team understands what went wrong.
    Anyhow any help would be very welcome as I don't want the same thing happening again.

    Thanks in advance for your help

    I had a somewhat similar experience a couple of months ago.


    I played most of the rehearsal and everything was going fine then I went for a solo near the end of the night and suffered major volume drop and my sound went all thin and tinny.


    I assumed the issue was the the KPA so I tried pushing buttons and switches but nothing helped. I rebooted the KPA still the same. Then I noticed that the sound was OK when using the Piezo pickup on my PRS. I rechecked the magnetic pickups again and found that the neck pickup was actually OK it was only the bridge pup that wasn't working.


    I re tested everything the next night at home and the problem was still there. So it was clear the issue was the guitar. The battery wasn't flat but was getting low so I changed it. No difference. I assumed I had a faulty pickup and was expecting to need a rewind.


    I took my guitar to a good guitar tech and we went through everything with the multimeter. The pickup read fine. We traced the problem to the selector switch. I cleaned it out and sprayed some contact cleaner. Everything worked perfectly again for over a week then the same problem returned. The PRS Hollowbody II has a circuit board in it so I started to think the issue might be related to the board. So I arranged to the guitar to a tech that deals with amps, synths etc . The night before I was due to take it to him everything started working perfectly again!


    I went anyway and described the problem and the steps taken to fix it. His response was immediate and clear. "The switch is dirty. Change it and everything will be fine. Trust me." He explained that the cleaner and process of cleaning had simply dislodged something which was causing a partial short. Also the newly exposed contacts would now be more prone to reoxidising.


    I still haven't changed the switch but I recleaned it again when I got home and it has been working perfectly since.


    I don't know if this is your problem or not but just want to stress that sometimes the problem is the least likely thing you could imagine and the only way to trace it is to be very meticulous about swapping out every possible cause (often several times are necessary with an intermittent fault) until you find the problem. I know you have already taken considerable steps to test this already but you may need to run through them again and think about anything else you might have missed.


    Best of luck and hope you track it down soon.


    Alan

    In my case the first time I used a different guitar than the second time.
    The only common thing between the two occurrences is the location (same rehearsal room with the same cab).
    But the owner/technician stated other guitar players using that cab had no problem and even loved the cab.

    Quote from MetalMauce

    In my case the first time I used a different guitar than the second time.
    The only common thing between the two occurrences is the location (same rehearsal room with the same cab).
    But the owner/technician stated other guitar players using that cab had no problem and even loved the cab.

    As that's the only common factor you need to disregard what then owner says and test for yourself with a cabinet you know definitely works to rule out the cab in the studio. If everything works with another cabinet in that studio then their cabinet would seem to be the issue. If not you either have an intermittent hardware issue with the Kemper power amp or something else in the signal path (if it is intermittent then it can work sometimes and not others so can be difficult to trace). Or, there is something else about that location which is playing up but I can't think what that would be.

    Quote from MetalMauce

    So reconnected the whole setup as it should be (my guitar, my wireless, into the Kemper, on the CAB from the rehearing room) -> no problem at all and I could play the whole night without any issues! WTF??

    You mention a wireless connection - have you tried using a cable instead? Could it be that your wireless connection is suffering from temporary external interference, causing the signal to get messy? That would explain why the same setup is at times unproblematic and faulty at other times...

    Yes, he mentioned replacing the wireless with a cable.


    To the OP, you simply don't have enough data to reach a conclusion. This is the nature of intermittent issues. Welcome to statistical problem solving. I don't believe that this forum will offer a response that will provide a definitive solution although you may get ideas that you have not considered. So far, you have been very logical in your test ideas. I think you are going to have to continue as you have. You will eventually determind if it is the Kemper or something else.

    Quote from lbieber

    Yes, he mentioned replacing the wireless with a cable.


    To the OP, you simply don't have enough data to reach a conclusion. This is the nature of intermittent issues. Welcome to statistical problem solving. I don't believe that this forum will offer a response that will provide a definitive solution although you may get ideas that you have not considered. So far, you have been very logical in your test ideas. I think you are going to have to continue as you have. You will eventually determind if it is the Kemper or something else.

    THank you for your response and confirmation on the steps I already took.
    It's the helpless feeling that's killing.
    I was thinking about this yesterday. Assuming that the problem is with the Kemper (I doubt it, but just in case and if so I suspect the internal poweramp), what I can do is:
    - Next time, try the same cab at the same rehearsal studio
    - Bring my Headrush FRFR as a backup to the internal poweramp (so I can use it on MONITOR OUT and bypass the cab)
    - Bring my Palmer MACH 402 as a backup to the internal poweramp (so I can use it on MONITOR OUT and use the cab).

    I was thinking bringing those two things would allow me some more steps to test if the problem occurs again.
    Would that be good thinking?