Impedance Rant

Discussion in 'Amp Central Station' started by JamesFlames714, Oct 18, 2021.

  1. JamesFlames714

    JamesFlames714 TDPRI Member

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    I just think it’s funny how much rhetoric/discussion/explanation there is available about speaker impedance/pairing heads with cabs etc and how little consensus there is in those discussions. People use so many different metaphors to explain it and people in various videos/comments/threads seem split 50-50 between ‘you must NEVER have mismatched impedance’ and ‘yeah man as long as the Ohms on the head r lower than the Ohms on the cab I just plug into whatever and RAWK OUT’. I felt I really had to have a solid understanding of all of this before I bought a head but trying to do that was making my head spin. Anyway, wish me luck at band practice this week when I go plug my new head into a loaner 4x10 at the hourly practice spot.
     
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  2. arlum

    arlum Tele-Afflicted Platinum Supporter

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    It's an important subject. If you own an expensive amp head you don't want to do anything that could cause it harm. Some amps can handle mismatches better than others. Some won't handle it at all. Many vintage amps and boutique amps that cost $$$$$ need a near perfect match. Certain production amps, (Mesa for example), do a pretty good job when lightly mismatched.
    Mesa has good info on this subject. It's proven itself to me over the long term.

    https://mesa-boogie.imgix.net/media/Amplitudes/2013/June/Speaker Impedance Matching and Hookup.pdf
     
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  3. kbold

    kbold Friend of Leo's

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    For valve amps, you need to match the speaker impedance with the amp impedance.
    Not connecting your speaker to a valve amp does very bad things.

    For a s/s amp, your speaker impedance just has to be above the minimum recommended.
     
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  4. Jakedog

    Jakedog Telefied Ad Free Member

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    People get REALLY uptight about this stuff. I’ve read a gazillion technical explanations why.

    This is what I know- I was taught to never go below what the amp is rated at. Stay at, or above rated impedance. I’ve been working with that rule for over 30 years. I’ve never broken an amp doing it. I’ve run 8 ohm heads into 16 ohm cabs, cranked and blazing, five nights a week, four sets a night, for YEARS. And not hurt a damned thing. Ever.

    I have also run an 8 ohm minimum load amp into a four ohm load and blown that sucker up in no time flat.

    So my rule is the “at or above” rule. It’s always worked for me. Decades of it. Tube and SS. It’s never failed.

    Disclaimer- I’ve never seriously pushed it. Like, I’ve never tried a 4 ohm amp into a 32 ohm load. But based on my experience I don’t think I’d be scared to. I’d just think it was a dumb idea cause really, what’re you hoping to get outta that?
     
  5. Dacious

    Dacious Doctor of Teleocity

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    Although some Fender vintage amps would tolerate a 100% mismatch it's never been recommended -
    Yes you can do it. In some cases with little penalty, but you are wearing out something faster.

    It's like, you can buy a new Corvette and drive it everywhere at legal speed in first gear. You won't even void your warranty. But you are shortening the life of at least the engine.

    Impedance matching is to match the alternating current impedance of the tubes to the speaker's impedance on the other side of the output or impedance matching transformer.

    Vintage Fenders especially 6L6 units tended to be mildly biased for moderate current draw and moderate preamp gain which means running everything a bit harder is no big deal. You'll wear tubes out a bit faster.

    EL84s like Vox and small Mesas - you really don't want to push them much harder usually they're at their rated limits. Especially not if you're pushing them hard with drive devices.

    I'd match the rated impedance of any EL84 amp. EL34, 6L6, maybe not so much.

    With solid state, you only need match the minimum rating. Because ss amps are current devices you want to limit high current draw on them which is what reducing impedance will do - most solid state devices put out more power (heat) as impedance goes down.

    Tubes will self-limit to some extent but there's enough blown output transformers around to suggest you can heat them up but good - that's when things melt. Tubes are also not that keen on pushing higher than rated loads although it's the output transformer that's the issue there.
     
    Last edited: Oct 18, 2021
  6. klasaine

    klasaine Poster Extraordinaire Silver Supporter

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    The confusion is the inherent problem with the internet, not the actual information. Way too many folks talking about $h1t they don't know anything about.

    Matched is what is recommended.
    Above is fine for the cab.
    Below is not recommended and depending on the heartiness or lack thereof of the head, you may blow the amp.

    With impedance mismatches there will be slight tonal and volume differences. You may like that.
     
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  7. Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    Impedance itself is something that's difficult to explain and for people understand.
     
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  8. sax4blues

    sax4blues Poster Extraordinaire

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    Why wouldn’t you just match?
     
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  9. bebopbrain

    bebopbrain Tele-Meister

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    Maybe put an ohm meter on the mystery 4x10 and see if it reads less than 2 ohms.
     
  10. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    This answer came from the late great Ted Weber:

    “Here are the straight facts on impedance mismatches, and hopefully it will explain why there are contradictory reports:

    ON A TUBE AMP
    It is okay to run a LOWER impedance cabinet or speaker than the amp’s output impedance. Usually a mismatch of 2:1 is okay. (i.e. amp at 16 ohms, cab at 8 ohms.) It is dangerous to run a HIGHER impedance cabinet or speaker, as there is a potential for flyback currents that could either cause a catastrophic failure, or the stress over time can cause long-term failure eventually. (although with a tube amp, it’s really best that you keep the impedance matched.) Amp power is not affected by mismatching.

    ON A SOLID STATE AMP
    It is okay to run a HIGHER impedance cabinet or speaker than the amp’s output impedance. (i.e. amp at 4 ohms, cab at 8 ohms.) It is dangerous to run a LOWER impedance cabinet or speaker. Amp power output is reduced, the higher the impedance.”


    For this, and other actual facts about speaker impedance, like how 'nominal' works here and why it’s not a fixed number, search his old Q&A page for “impedance.”

    https://www.tedweber.com/lets-talk-speakers-q-a/
     
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  11. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    For example;
    :lol:Take your pick...........:twisted:
     
  12. BigDaddyLH

    BigDaddyLH Tele Axpert Ad Free Member

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    [​IMG]
     
  13. Killing Floor

    Killing Floor Poster Extraordinaire Silver Supporter

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    Better to ruin someone else’s gear than your own.
     
  14. fasteddie42

    fasteddie42 Tele-Afflicted

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    because of all the confusion on this subject, I've found the easiest path for me is to always use the recommended impedance.

    no guess work.
     
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  15. Dan German

    Dan German Doctor of Teleocity Silver Supporter

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    Man, I know what you’re saying; kids these days have no respect, and they will give you lip about… what? Oh, IMPEDANCE?? I thought you said IMPUDENCE. Never mind, carry on. I’ll just go back to my meditation.

    Ohm…
    Ohm…
    Ohm…

    (And for the record, not trusting anything I read or hear, I’ve just stuck to matching the impedance to the “correct” value at all times.)
     
  16. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    LOL, you're right, this thread certainly supports the OP's idea there's a lot of different info out there. I don't know which answer is 'right.' (You, Bendyha, surely do.) I'm just saying I like to get my internet info from known reliable sources, and cite 'em, and Ted Weber knew more than most of us ordinary citizens who share opinions. Full respect, though, to Jakedog, who has a lot more experience than I do. I didn't realize the Ted answer seemed opposite to his.
     
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  17. Tim S

    Tim S Tele-Afflicted Gold Supporter

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    This isn’t difficult. Do what the amp manufacture says.

    The people who engineered the product know its capabilities better than anyone who makes general statements.
     
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  18. Lone_Poor_Boy

    Lone_Poor_Boy Tele-Holic

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    Excellent pdf linked. Thank you.

     
  19. beanluc

    beanluc Tele-Afflicted

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    By "ohm meter" are you ruling out an instrument which measures DC resistance in ohms? Do you mean to specify something which measures AC impedance?

    Is there a risk of measuring the wrong thing with the wrong meter?

    I don't know, I'm asking.
     
  20. Wally

    Wally Telefied Ad Free Member

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    As I understand it, pertaining to tube amps there are dangers in mismatching to either side of the suggested impedance. Mismatching to the low side places the stress on the primary side of the output transformer…mainly the power tubes. Of course, a stressed power tube is more likely to suffer a failure. If that failure is catastrophic, the OT could be taken out. Mismatching to the high side places the stress on the secondary side of the OT…..the possibility of flyback voltage damaging the windings. That damage does not have to be total and catastrophic. The OT can continue to function albeit with lower output power and degraded Sonic quality….depending on the amount of piercing of the winding’s insulation occurs.
    Mismatching to either side yields change in the sound and output. Everything I have ever read states that a matched load allows the OT to operate most efficiently in the safest manner while delivering its designed output.
    I run matched loads. What someone else does is not my concern….until it is time to replace the transformer.

    The situation with solid state amplification is a starker reality. If you mismatch to the lower side, the changes are great that the output section of the amp will burn down in short order. If you mismatch to the high side, the output is drastically reduced…but at least the output section of the amp is safe.
     
    Last edited: Oct 18, 2021
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