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发表于 2010-8-19 11:58:13
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我帮你找了一个比较有说服力的答案----不行
但箱子坏不坏取决于具体的设计.注意这是说 管箱. 具体原因会看英文的自己看. 反正是让我开了眼界.
你下一个问题是如何将 16 的cab变 8, 答案是可以的.学习一下电阻串联与并联.
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http://aga.rru.com/
Can I plug a X-ohm cabinet into a Y-ohm head? Several answers are provided: Rich's short answer, Miles's fairly short answer, LV's long answer, and StratMatt's non-technical answer. Rich's answer:
``NO!!!!!!!!!!!!!!!''
Short answer:
In general, you should match impedances. If you must mismatch, mismatch in the right direction, but stay as close as possible. So what's the right direction?
With tube gear it's better to have the speaker impedance lower. Connecting a 4 ohm load to an 8 ohm amp may be OK, but connecting a 16 ohm load to an 8 ohm amp is probably not. Connecting a 16 ohm load to a 4 ohm or 2 ohm amp is begging to destroy the amp. Running too high of a load on tube gear can fry anything (and occasionally everything) in the outputs, including tubes, transformers, resistors and tube sockets.
With solid state gear it's better to run a higher impedance. Connecting an 8 ohm load to a 4 ohm amp should be fine. Running too low of a load with solid state will fry your output transistors, and possibly more.
For more information, and to see when you might be able to get away with impedance mismatching in the wrong direction, see LV's explanation ("Long Answer") below and the AGA Technical FAQ.
-Miles
Long Answer:
Actually, this thread pops up every month or so. It always winds up the same way, too... the guys who know their stuff tell everyone that it's not a good idea to run a tube amp at a higher load impedance than it's looking for, and a bunch of other dudes chime in with "Oh Yeah? I ran my (whatever) into a 16-ohm cabinet for years and it was rated for 8 ohms. What about that?"
Well, this is what about it: sometimes it'll be OK. Things are different from amp to amp; playing style and signal type factor into the equation, too. A player who plays loud, with lots of treble, through an amp with high plate voltage (old Marshall, Orange, Music Man, older Ampegs, etc.) is much more likely to wind up with arced sockets (or worse) than a dude who plays jazz, with bassy tone, through a Fender amp with 430V on the plates. The type of mismatch matters, too... running an 8-ohm amp into a 16-ohm cabinet is less likely to cause problems than running a 4-ohm amp into a 16-ohm box. Running a downward mismatch will eat your tubes up a bit faster, but if your amp has a good output tranny that's probably the only thing that will happen.
Older Fenders have an extension speaker jack that's wired in parallel with the main one; if you plug an extension cab into a Twin Reverb (for instance) the load will be lower than 4 ohms, no matter what the box is rated at. If the amp was going to be damaged by running a load that was lower than the rated impedance, it stands to reason that Fender would have wired the jacks in series. They didn't, though.
A downward mismatch is usually OK, or at least it's better than the upward variety. I see a few Super Reverbs every year that have been re-speakered by their owners; they go to a lot of trouble to find out how to do a series-parallel hookup for the speakers because they "know" that the amp should be running an 8-ohm load. All of a sudden, the amp starts sounding like crap and blowing fuses. A Super Reverb wants a 2-ohm load; running it at 8 ohms pretty well guarantees you'll be making a substantial contribution to the Lord Valve Home for Lord Valve. (My favorite charity.) Of course, there will be a few "experts" who are convinced that SS amps and tube amps respond to improper loading in the same way. They're wrong, no matter how loudly they may screech.
As far as solid state amps go, it's a lot more straightforward... if you go below the rated impedance, you're going to smoke something unless the amp has really good current limiting in the output stage. Running a higher-than-rated impedance is just fine... you get less power output, of course, but the amp will run cooler and last longer. You can run a SS amp into an open circuit 'til the cows come home, and it won't do jack to it. Run a tube amp into an open, and you'll probably arc a socket (or worse) with the first note you play. It's a really common failure; I do three or four a week, year in, year out.
-Lord Valve
StratMatt's non-technical explantion:
I wanted to know the facts on this so I asked Mike Soldano when I picked up my amp. After explaining it to me in detail (as he does with all my tube amp newbie questions) I asked if this was an accurate way to put it (in simple non-tech terms).... If the amp is designed for 8 ohm load and you are running it with an 8 ohm speaker load the speakers are using 100% of the power that the primary winding of the transformer is refilling to the secondary winding of the transformer. Now if you run a higher speaker load like 16 ohms or more (or no speaker load), since the resistance is higher than the transformer expects to see the power leaving the transformer can't get out as fast because its path is restricted by the higher resistance/impedance. So now only 60% (for example- I'm just making up this number) of the power has been able to leave the secondary wiring of the transformer and there is 40% left in there. The primary winding of the transformer now refills the 100% it always refills to the secondary that still has 40% in it. Obviously the transformer was not designed to cope with 140% of it's design load. Over and over this repeats with power remaining in the secondary- and it keeps stacking hihgher and higher until it gets so overloaded and hot that the insulation melts and you get arcing and all that fun stuff.
Mike said this was a somewhat accurate way to put it in simple non-tech terms.
So that is my understanding of it. And I am definitely not a tech!
-StratMatt
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http://www.geofex.com/tubeampfaq/tubefaq.htm#transformers
Q:Will it hurt my amp/output transformer/tubes to use a mismatched speaker load?
Simple A: Within reason, no.
Say for example you have two eight ohm speakers, and you want to hookthem up to an amp with 4, 8, and 16 ohm taps. How do you hook them up?
For most power out, put them in series and tie them to the 16 ohm tap, or parallel them and tie the pair to the 4 ohm load.
For tone? Try it several different ways andsee which you like best. "Tone" is not a single valued quantity,either, and in fact depends hugely on the person listening. Thatvariation in impedance versus frequency and the variation in outputpower versus impedance and the variation in impedance with loadingconspire to make the audio response curves a broad hump with ragged,humped ends, and those humps and dips are what makes for the "tone" youhear and interpret. Will you hurt the transformer if you parallel themto four ohms and hook them to the 8 ohm tap? Almost certainly not. Ifyou parallel them and hook them to the 16 ohm tap? Extremely unlikely.In fact, you probably won't hurt the transformer if you short theoutputs. If you series them and hook them to the 8 ohm or 4 ohm tap?Unlikely - however... the thing you CAN do to hurt a tube outputtransformer is to put too high an ohmage load on it. If you open theoutputs, the energy that gets stored in the magnetic core has nowhereto go if there is a sudden discontinuity in the drive, and acts like adischarging inductor. This can generate voltage spikes that can punchthrough the insulation inside the transformer and short the windings. Iwould not go above double the rated load on any tap. And NEVER opencircuit the output of a tube amp - it can fry the transformer in acouple of ways.
Extended A: It's almost never low impedance that kills an OT, it's too high an impedance.
The power tubes simply refuse to put out allthat much more current with a lower-impedance load, so death byoverheating with a too-low load is all but impossible - not totally outof the question but extremely unlikely. The power tubes simply get intoa loading range where their output power goes down from the mismatchedload. At 2:1 lower-than-matched load is not unreasonable at all.
If you do too high a load, the power tubes still limit what they put out, but a second order effect becomes important.
There is magnetic leakage from primary tosecondary and between both half-primaries to each other. When thecurrent in the primary is driven to be discontinuous, you get inductivekickback from the leakage inductances in the form of a voltage spike.
This voltage spike can punch throughinsulation or flash over sockets, and the spike is sitting on top ofB+, so it's got a head start for a flashover to ground. If thepunchthrough was one time, it wouldn't be a problem, but the burningresidues inside the transformer make punchthrough easier at the samepoint on the next cycle, and eventually erode the insulation to make aconductive path between layers. The sound goes south, and with anintermittent short you can get a permanent short, or the wire can burnthough to give you an open there, and now you have a dead transformer.
So how much loading is too high? For a welldesigned (equals interleaved, tightly coupled, low leakage inductances,like a fine, high quality hifi) OT, you can easily withstand a 2:1mismatch high.
For a poorly designed (high leakage, poorcoupling, not well insulated or potted) transformer, 2:1 may well bemarginal. Worse, if you have an intermittent contact in the path to thespeaker, you will introduce transients that are sharper and hence causehigher voltages. In that light, the speaker impedance selector switchcould kill OT's if two ways - if it's a break befor make, thetransients cause punch through; if it's a make before break, the OT isintermittently shorted and the higher currents cause burns on theswitch that eventually make it into a break before make. Turning thespeaker impedance selector with an amp running is something I would notchance, not once.
For why Marshalls are extra sensitive, couldbe the transformer design, could be that selector switch. I personallywould not worry too much about a 2:1 mismatch too low, but I might notdo a mismatch high on Marshalls with the observed data that they arenot all that sturdy under that load. In that light, pulling two tubesand leaving the impedance switch alone might not be too bad, as theremaining tubes are running into a too-low rather than too-high load.
[ 本帖最后由 triangle 于 2010-8-19 12:02 编辑 ] |
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