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  • Didn't blow up my amp today

    Lugged my second 4x12 into my rehearsal space today and hooked it up. Amp is an EVH 5153, early serial. Forgot to switch the output selector over from 16 to 8. Played for 10 - 15 minutes or so before auddenly realising my mistake. Switch the amp off, set it to 8 ohm out, turned back on. Played for another hour. Output tranny seems fine - no smoke, no smell, no horrifyingly loud silence. Guess I dodged a potentially very expensive bullet.

    My only questions is... why? Conventional wisdom says you can connect a speaker load with higher impedance than the output and you'll be fine (I've tried it before - there's some tone suck but that's pretty much it) but shouldn't connect a lower load to the amp lest you'll send it to amp heaven.
    --------------------------------------------------------
    1973 Aria 551
    1984 Larrivee RS-4 w/ EMG SA/SA/89
    1989 Charvel 750 XL w/ DMZ Tone Zone & Air Norton
    1990's noname crap-o-caster plywood P/J Bass
    1991 Heartfield Elan III w/ DMZ mystery pups
    1995 Aria Pro II TA-65
    2001 Gibson Les Paul Gothic w/ PG-1 & SH-8

  • #2
    Re: Didn't blow up my amp today

    I think it really depends on the design of the amp. Some amps don't tolerate mismatches well, and tubes will wear faster. Some do (my Mesa does) and you can use mismatches to change the tone. I never thought 10 minutes or so would kill an amp, though.
    Dave, Ambassador/Writer/Artist for Seymour Duncan

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    • #3
      Re: Didn't blow up my amp today

      Originally posted by Mincer View Post
      ... I never thought 10 minutes or so would kill an amp, though.
      +1
      Sanford: "The hardest part about tone chasing is losing the expectations associated with the hardware."

      Comment


      • #4
        Re: Didn't blow up my amp today

        Originally posted by Coma View Post
        Lugged my second 4x12 into my rehearsal space today and hooked it up. Amp is an EVH 5153, early serial. Forgot to switch the output selector over from 16 to 8. Played for 10 - 15 minutes or so before auddenly realising my mistake. Switch the amp off, set it to 8 ohm out, turned back on. Played for another hour. Output tranny seems fine - no smoke, no smell, no horrifyingly loud silence. Guess I dodged a potentially very expensive bullet.

        My only questions is... why? Conventional wisdom says you can connect a speaker load with higher impedance than the output and you'll be fine (I've tried it before - there's some tone suck but that's pretty much it) but shouldn't connect a lower load to the amp lest you'll send it to amp heaven.
        Review the Maximum Power Transfer Theorem. If the amp internal impedance and the load (speaker) impedance do not match, the amplifier dissipates the excess power not reaching the speaker.

        It is actually the inverse scenario of what you describe.

        When the speaker impedance is lower than what the amp is set for, it is the tubes dissipating the excess power. This is harder on your tubes.

        When the speaker impedance is higher than what the amp is set for, it is the transformer dissipating the excess power. This is harder on the transformer and the transformer runs a hotter.

        I avoid mismatching as I have never noticed any improvement in tone. Still many people and even some manufacturers will tell you a mismatch of one tap (16 ohm to 8 ohm, 8 ohm to 16 ohm, 8 ohm to 4 ohm or 4 ohm to 8 ohm) will not damage your amp. This has to do with impedance varying with frequency. Also manufacturers over-engineering the transformer size for a safety factor.

        What kills transformers is no speaker load. This is the case of speaker impedance being much higher than what the amp is set for. Actually an infinite ohm speaker. In this case all the power is dissipating in the transformer. This is why you never run a tube amp without a speaker load.
        I miss the '80s (girls) !!!

        Seymour Duncans currently in use - In Les Pauls: Custom(b)/Jazz(n), Distortion(b)/Jazz(n), 59(b)/59(n) w/A4 mag, P-Rails(b)/P-Rails(n); In a Bullet S-3: P-Rails(b)/stock/Vintage Stack Tele(n); In a Dot: Seth Lover(b)/Seth Lover(n); In a Del Mar: Mag Mic; In a Lead II: Custom Shop Fender X-1(b)

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        • #5
          Re: Didn't blow up my amp today

          As a rule of thumb:

          You can safely use higher impedance speakers with SS amp no problem, but lose lot of power important for SS amps. Which is what I think was referred in original post.

          With tube amp you want to use lower impedance speakers for the reasons JamesPaul very well explained above.
          "So understand/Don't waste your time always searching for those wasted years/Face up, make your stand/And realize you're living in the golden years"
          Iron Maiden - Wasted Years

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          • #6
            Re: Didn't blow up my amp today

            yes and no, you dont want to go too low on a tube amp. an 8 ohm ot tap doesnt want to see a 2 ohm load on even a good amp for long. the power tubes will suffer since its the relationship between speaker and tubes the ot is dealing with. you are 100% correct on a ss amp, you dont want to go low since the amp may see it as a short and give up the smoke but higher is ok. youll just get less power. 99.9% of the time, its best to match things properly

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            • #7
              Re: Didn't blow up my amp today

              Originally posted by jeremy View Post
              yes and no, you dont want to go too low on a tube amp. an 8 ohm ot tap doesnt want to see a 2 ohm load on even a good amp for long. the power tubes will suffer since its the relationship between speaker and tubes the ot is dealing with. you are 100% correct on a ss amp, you dont want to go low since the amp may see it as a short and give up the smoke but higher is ok. youll just get less power. 99.9% of the time, its best to match things properly
              I thought that obvious from earlier posts in this thread, but good to point out.

              You should always use matching impedance in tube amps in general, but it's safer to go lower than higher if you can't.
              Last edited by Jacew; 01-08-2020, 11:01 PM.
              "So understand/Don't waste your time always searching for those wasted years/Face up, make your stand/And realize you're living in the golden years"
              Iron Maiden - Wasted Years

              Comment


              • #8
                Re: Didn't blow up my amp today

                People on the interwebs get very worked up about this stuff (duh), but honestly, having the selector switch on the wrong setting won't really hurt most good quality tube amps. It may put a little more wear on the tubes depending on which way the setting goes, but transformers, again, good quality, should be overdesigned enough that it doesn't bother them. Can't speak to some of the MIC amps where they have cut every corner possible, but I would still bet the transformer is stout enough to be fine.

                Some of the Fenders heads, the Tone Master (?), had settings of high, medium, and low on the selector and you were encouraged to experiment to find the one that sounded right for you.

                That said, don't run them below 4 ohms or above 16, and yes it is best to keep things matched. But having the switch set wrong is nothing to freak out about. Running without a cab, yeah, that's bad, but still, if it takes you few minutes to figure out why you don't have any sound coming out, probably not going to smoke it, any good designer would have realized that stuff like this will happen and design it well enough to prevent "reasonable" catastrophic failure. The industry term is FMEA, Failure Modes and Effects Analysis, which is done on most products, or at least should be. If you are in the medical field, it is required and reviewed by the FDA, in aerospace, if people are involved it is highly reviewed, if it's a satellite, failure to find potential failures can cost hundreds of 100s if not millions of $. But as recent news has shown, stuff can slip through the cracks of the biggest and best companies (Boeing).

                Comment


                • #9
                  Re: Didn't blow up my amp today

                  My buddy from the UK who has passed now did a whole US tour with his Marshall JCM800 2203 set accidentally to 16 on a 8 ohm cab.

                  On one of the very last shows of the tour, I noticed it when I shared his rig in Asheville NC

                  Didn't hurt anything after 40 shows -just changed the tone slightly.
                  “For me, when everything goes wrong – that’s when adventure starts.” Yvonne Chouinard

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                  • #10
                    Re: Didn't blow up my amp today

                    From the Tone Master Manual, again, not saying this is true for all amps:

                    D. IMPEDANCE SWITCH - This is labeled LO, MED and HI. This switch serves two functions.
                    One, to set the output impedance of the amplifier to best match the speaker impedance for
                    maximum power. Second, to enable the amplifier to better achieve the cranked-up sound at a lower
                    volume. On the B CHANNEL, with a single Tone-Master enclosure, this switch should be set
                    according to the setting of the B CHANNEL volume knob: For volume settings of 3.5 and lower,
                    LO would be the appropriate setting. For settings of 3.5 to 7, MED is best. For settings above 7,
                    HI will produce full power and tone. This switch will not damage tubes or reduce tube life at
                    these settings. What it does do is increase the gain in the LO and MED settings and thereby better approximate the Full volume sound at a lower level than by adjusting the VOLUME alone.
                    With a single 16Ω enclosure, LO will produce 30 watts, MED will Produce 60 watts, and HI will
                    produce a full 100 watts. With two 16Ω enclosures, (an 8Ω load), LO will produce 60 watts, and
                    MED will Produce 100 watts. In the A CHANNEL, the switch has the same function, although
                    blues players may like running the switch on LO all the time to get that great crying tone.
                    Conversely, a player looking for a New Wave Strat® tone might like the sound of the A CHANNEL
                    on HI.

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                    • #11
                      Re: Didn't blow up my amp today

                      that was such a cool amp!

                      Comment


                      • #12
                        Re: Didn't blow up my amp today

                        Refreshing to see a couple of people understand that tube amps and solid state amps operate differently, and that speakers impedance and amp output impedance mismatch is different for tube amps and solid state.
                        Last edited by PFDarkside; 01-11-2020, 08:38 AM.
                        Oh no.....


                        Oh Yeah!

                        Comment


                        • #13
                          Re: Didn't blow up my amp today

                          Originally posted by devastone View Post
                          People on the interwebs get very worked up about this stuff (duh), but honestly, having the selector switch on the wrong setting won't really hurt most good quality tube amps. It may put a little more wear on the tubes depending on which way the setting goes, but transformers, again, good quality, should be overdesigned enough that it doesn't bother them. Can't speak to some of the MIC amps where they have cut every corner possible, but I would still bet the transformer is stout enough to be fine.

                          Some of the Fenders heads, the Tone Master (?), had settings of high, medium, and low on the selector and you were encouraged to experiment to find the one that sounded right for you.

                          That said, don't run them below 4 ohms or above 16, and yes it is best to keep things matched. But having the switch set wrong is nothing to freak out about. Running without a cab, yeah, that's bad, but still, if it takes you few minutes to figure out why you don't have any sound coming out, probably not going to smoke it, any good designer would have realized that stuff like this will happen and design it well enough to prevent "reasonable" catastrophic failure. The industry term is FMEA, Failure Modes and Effects Analysis, which is done on most products, or at least should be. If you are in the medical field, it is required and reviewed by the FDA, in aerospace, if people are involved it is highly reviewed, if it's a satellite, failure to find potential failures can cost hundreds of 100s if not millions of $. But as recent news has shown, stuff can slip through the cracks of the biggest and best companies (Boeing).
                          I once forgot to connect Orange TT to speaker. Burning smell coming out of it almost right away made me realize that mistake very quickly.

                          Didn't break anything though.
                          "So understand/Don't waste your time always searching for those wasted years/Face up, make your stand/And realize you're living in the golden years"
                          Iron Maiden - Wasted Years

                          Comment


                          • #14
                            Re: Didn't blow up my amp today

                            Originally posted by Jacew View Post
                            I once forgot to connect Orange TT to speaker. Burning smell coming out of it almost right away made me realize that mistake very quickly.

                            Didn't break anything though.
                            Yeah, that's why I'm trying to be careful to say "probably", "most of the time", "most amps" (meaning not all). I've done that with old Marshalls and took me a few to figure out why there wasn't any sound, but yeah, they don't build them like they used to, or maybe I just got really lucky.

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                            • #15
                              Re: Didn't blow up my amp today

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