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16 ohm speaker into an a 8 ohm output, ok?

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  • 16 ohm speaker into an a 8 ohm output, ok?

    Just nailed a pretty solid deal on a Mesa nomad 55 1x12 combo. I already have a nice worn in vintage 30 rated at 16 ohms 60 watts I'd like to put in this amp. The Mesa has one 8 ohm out and 2x 4 ohms outs. I can run my speaker from the 8 ohm out right? I know this isn't really a prob with solid state amps but is it the same for tube amps? Will I lose any power if I do? I Think it might be ok but I just wanna make sure.
    -"Who is John Galt?"-

  • #2

    Sounds like a bad idea.
    You don't ever want to run into a load that is higher impedance (more resistance/load) than the amp is designed for because you might kill the tranny.

    Several years ago I asked Mike Soldano if there is a correct way to mismatch impedance and, if so, why it won't hurt the amp.
    He said that running a higher load than the amp is designed for is really bad, but that a lower load is okay, but you wouldn't want to mismatch by more than one "notch". Running an 8 ohm amp into a 4 ohm load is fine, but mismatching any further would not be a good idea. You can run an 8 ohm head into a 4 ohm load, your tubes will just wear out a little faster. You cannot run an 8 ohm head into a higher resistance without

    possible damage.

    You do not want to run into a higher resistance than your amp is designed for because the power created in the power transformer cannot get out of the

    transformer as quickly or completely as it was designed to, so there is power left in it that should not be there. 

    If 100% of the power created by the primary winding of the transformer cannot escape from the secondary winding by going out to an equal (or lesser)

    resistance than designed for, that power which is trapped in the secondary winding will continue to stack/increase as the primary winding continues to

    refill this secondary winding at the normal rate of 100% of the power it was designed for.  This excess power must go somewhere... the insulation melts and

    you get a blown tranny and possibly a fried tube and socket.

    Soldano's standard 50+ watt amps have a a load selector switch to select which ohm setting you want, but the 20 watt Astroverb does not have this switch so

    he designed the Astroverb to run into a 16 ohm load so that no matter what you plug into (4 ohm cab, 8 ohm cab, 16 ohm cab) you never plug into a higher

    load than the amp wants. Mike said that running the 16 ohm Astroverb into 8 ohms simply makes the tubes run a little hotter so they wear slightly faster.

    DR Strings > '97 Mexi Strat: USACG neck & Super Vee Blade Runner > Duncan TB-11 Custom Custom, Fender Original '57/'62 > Barber Direct Drive > Soldano Astroverb > WGS RETRO 30 (replaced Vintage 30) in Avatar 2x12. DD-5 Delay, Chorus. Fender Blues Junior III (BillMAudio mods in the mail)


    • HKSblade2
      HKSblade2 commented
      Editing a comment

      Not usually a good idea. Read up on OT flyback voltage. IIRC Weber had a great article about high impedance loads on low impedance outputs.

      I know a ton of people who ran 16 ohm cabs on 8 ohm out loads and were fine. Doesn't mean it's ever the right thing to do. Would I recommend it? Not really. See if you can find a used 8 ohm speaker for $50-75.

      Contact Mesa support and see what advice they have if you are concerned about any amp damage.

  • #3
    As always fellas I really appreciate the help. Say what you will about the v30, it's a great speaker and is the only thing that made my valve king bearable. I'm pretty excited about my Mesa, as it's definitely the nicest amp I've ever owned, can't wait to get it. I hate to see my v30 go but I was already looking into a scumback just in case the impedence was gonna be an issue. Though maybe I'll take a look at those warehouse guitar speakers or whatever theyre called. I have heard good things about them. Soooo anyone interested in a peavey valveking 1x12 with a Celestion v30??!! Heh heh.
    -"Who is John Galt?"-


    • WittyMonikerHere
      WittyMonikerHere commented
      Editing a comment

      Hold on, I have a related question: I currently have a 2x12 8 ohm mono cab that has two 16 ohm Eminence Wizards wired in paralell. I wanted to swap out the speakers and retain the 8 ohm output to maximize compatability, so I was told getting two V30s @ 16 ohms would do the trick. This info accurate?


  • #4

    Tube amps use an output transformer to filter DC voltage (from the tube's bias circuit) from the AC waveform (the amplified audio signal), and to match the output impedance to the load impedance.

    The output transformer has taps at different locations on the output coil to match the output impedance to different load impedances, depending on which tap you use. When the impdances are matched, most of the amplifier's power is being transferred to the speakers and there's very little (negligible) energy being dissipated by the transformer. When the output impedances do not match, the transformer isn't transferring all of the energy to the speakers and must dissipate the energy somehow... usually as HEAT.

    If the load impedance is too low, there is much more current flowing on the output side of the transformer, this can damage the transformer and/or the speakers. If the load impedance is too high, there is much more current flowing on the amplifier side of the transformer, which can damage the transformer or the amplifier itself.

    Keep in mind that the difference between 4 ohms and 8 ohms is a factor of 2. The difference between 4 ohms and 16 ohms is a factor of 4. If you have a 4 ohm load connected to the 8 ohm tap, there's twice the current flowing on the output side. If you have a 4 ohm load connected to the 16 ohm tap, there's four times the current flowing. That extra current isn't flowing to the speakers either, it's building up in the transformer and turning into heat... which will eventually damage it.