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Amp ohm and attenuator damage

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  • Amp ohm and attenuator damage

    Hello. I got a 50w evh amp recently with cab but I’ve been playing through my Marshall cab instead since it’s broken in. Yesterday I decided to start breaking in the new cab. Marshall is 8ohm EVH cab is 16ohm. No problem amp has a switch for either, but I left my 8ohm attenuator plugged in(in the off position) I ran the amp and cab for an hour or so. When I realized what I had done, I shut it down and unplugged the attenuator and realized I was still losing about 10db with it through the off attenuator. So it’s possible I did damage to the amp I guess. I’m wondering what you guys think? I played it a little today and nothing odd but I’m wondering if I could/should send it in for repair at my local shop to prevent a full melt down.

  • #2
    Are you measuring decibels with a meter ?
    Just curious.
    id say plug in one amp / one cab / one guitar and see if everything works.
    If it does then get rid of everything else and consider yourself lucky.
    To be honest an attenuator with 2 cabs makes no practical sense.

    Comment


    • #3
      My understanding is you might have just shortened the life of some components by running a 16ohm amp into an 8ohm load for a little while, but if it didn't completely fail, you'll probably be able to just keep going as long as you don't do that again.

      But if you're worried and can afford a service call, it wouldn't hurt to have a tech measure the components and circuit and check how they are performing, just to make sure there isn't any indication of an imminent failure.

      Comment


      • #4
        IME tube amps are pretty forgiving and I think it's unlikely that you've done any real damage.
        I've run 8 Ohm outputs into 16 Ohm cabs for years of heavy gigging without any problems.
        The opposite mismatch might be more stressful however - I don't recommend running a 4 Ohm cab off a 16Ohm output, for instance.

        I think it's likely that even with the attenuation off, the impedance matching part of your attenuator is still active.
        The slight volume drop you're hearing might simply be due to the impedance.
        When I used to run my 16 Ohm Marshall cab from an 8 Ohm output of my Boogie, I did it to reduce the volume a bit.

        I suggest trying your rig with the attenuator plugged in but turned off, then trying again with the amp plugged straight into the cab.
        There might be a difference. Then again, there might not. But at least you'll know if your attenuator is full bypass.
        .
        "Brains have been washed. Fear has been mongered. Now we prepare for the final stage of our conspiracy theory." - Isle Of Dogs

        .

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        • #5
          If you hurt anything you would instantly know it. Even Dave Freidman said on his podcast that you could run a tube amp for awhile without anything for load, granted the volume wasn't turned up on the head for a long time. It would eventually overheat but would take awhile, and if the volume was turned down it is unlikely to build much heat for awhile.

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          • #6
            Ok. To be clear it was only the 1 amp and the 1 cab. 16ohm out of the amp into an 8ohm attenuator and then into the 16ohm cab. Everything sounds normal today so I’m guessing it’s fine but I don’t want to find out in a month the amp catches on fire or something.

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            • #7
              I think 16ohm amp into 8ohm attenuator, the amp would have been trying to open up, but you weren't hearing it, because...
              ...8ohm attenuator into 16ohm cab, that lowered your volume.
              I don't think it hurt the amp any more than running it wide open on 11 with a proper 4x12 would

              Comment


              • #8
                Originally posted by beaubrummels View Post
                I think 16ohm amp into 8ohm attenuator, the amp would have been trying to open up, but you weren't hearing it, because...
                ...8ohm attenuator into 16ohm cab, that lowered your volume.
                I don't think it hurt the amp any more than running it wide open on 11 with a proper 4x12 would
                Running it wide open into a 4x12 would hurt you far more than it would the amp.

                Sent from my SM-A115A using Tapatalk

                Comment


                • #9
                  Originally posted by dave74 View Post
                  If you hurt anything you would instantly know it. Even Dave Freidman said on his podcast that you could run a tube amp for awhile without anything for load, granted the volume wasn't turned up on the head for a long time. It would eventually overheat but would take awhile, and if the volume was turned down it is unlikely to build much heat for awhile.
                  Friedman would tell you "for best results always correctly match impedance."

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                  • #10
                    Were you running it on 10 or 2? If 2, it should be fine, if 10, well, honestly, if it didn't smoke then, it's most likely fine.

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                    • #11
                      Originally posted by JMP/HBE View Post

                      Friedman would tell you "for best results always correctly match impedance."
                      Yes of course he would, but in this case he was answering a question about accidentally having the amp running for awhile when the owner had forgotten that he had unplugged the cab for whatever reason. It was very close to the OP's question but more extreme.

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                      • #12
                        The amp was only running at 2 volume so I think it’s fine. Thanks for the reassurance y’all.

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                        • #13
                          A mismatch is a mismatch regardless of volume.
                          Mesa Boogie amps can tolerate certain mismatches because their output transformers are spec'd for it by Randall Smith.
                          EVH amps are made in Mexico or Indonesia and are not on par with Mesa Engineering.
                          JMP/HBE
                          Ultimate Tone Slacker
                          Last edited by JMP/HBE; 06-22-2022, 07:54 PM.

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                          • #14
                            No, current = volume, current is what would do damage. You can leave an amp on for a week without a speaker plugged in as long as you have the volume on zero.

                            Feel free to ask Dave.

                            Comment


                            • #15
                              Originally posted by devastone View Post
                              No, current = volume, current is what would do damage. You can leave an amp on for a week without a speaker plugged in as long as you have the volume on zero.

                              Feel free to ask Dave.
                              Dave Friedman and i are friends have chatted many times and he's done work for me.
                              So lemme get this starlight you're actually telling a noob [OP] who has just about fried his amp by doing the wrong thing that David Friedman of all people [in a 3rd party sense] is telling him to hook up his amp with no speaker load and leave it on for days ?
                              My how internet amp forums have gone down the sheeter.

                              Comment

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