Two Amps One Pair Of Speakers

I've read posts here on audiogon stating not to connect two amplifiers to one pair of speakers because (as it was put) the stronger amp will win if they are both on at the same time. To me, this means that one amp will likely have a fuse blown - however, I wonder if this is even true at all and I am curious to know if anyone out there has connected two amps to one set of speakers.

Now - I am not talking about bi-amping from a single source. I am talking about two separate systems connected to a single pair of speakers.

Of course having amps sending signal at the same time wouldn't make for good listening but even if they were, wouldn't the speakers just play both sources? Power flows from + ...> - so the positive output of both amps would flow through the speakers into the - of both amps wouldn't it??

Perhaps its just me but that seems more likely than something blowing up... but then again, what do I know?

Even in cases where someone bi-amps in a single system, there are two amps driving the speaker which in many/most cases is connected internally via crossover - regardless of how many binding posts are on the speaker. This is tried and true - lots of people bi-amp but why would it not cause damage but connecting two amps from different sources cause a problem?

Sorry for the rant, I hope someone can shed some technical knowledge on this.
Well, I'm no EE, but it seems to me that electricity always takes the easiest path. If another amp is connected to the output of the first amp(at the speaker terminals) the speaker has an impedance load of about 8 ohms, and the other amp has an output impedance of near zero ohms. Now, I don't know how an output impedance works in reverse, but it seems to me that the majority of the power will be diverted into the non-used amp, and try to drive it in reverse. I don't know if this would do anything to the output transistors or tubes. I do know that if the non-used amp is a transformer coupled tube amp, that the driving amp will "see" the load characteristics of the other tube amp's output transformer, and it will act like an inductor in the crossover network. This will screw up sound for sure. And if any damage may occur, that would be even worse than bad sound.

If you want to use the same speakers for 2 different systems, it is much better to get a switch box with 2-in and 1-out, and switch to the one you want to use. It may have some small sonic affect, but not near as much as loading the output of your amp, with another amp's output stage. Any parts in the other amp that can react to the signal, will react to the signal, and will cause changes in your music at the very least, and possibly damage something. Not sure about that part of it. There are just some things that you don't do.
As TW1 put it, Electricity will travel the path of least resistance, ence it will go to the outputs of the other amp.
Output stages can't deal with that, the output will be complitly burn, output transistor are directional they don't work bidirectional, they will blow. unless the other
amp has some kind of output protection circuit that will prevent the signal from entering the output circuit.

P.S. I don't have a EE but I have an AS on Electrical Engineering technology.

So please don't try it. Or you will be sorry you did.
Hey - now that makes sense! Thanks guys for your input on this topic. I dislike the idea of a switch box but I certainly dislike the idea of a damaged amplifier more.
Just for the record, there are amplifiers on the market that you can run in bridged mode (a topology that connects two amps to the same speaker with one amp serving the plus pole, the other the minus pole and a connection between the amps).

I believe the Pass X1000 falls into that category. Accuphase has or had a such amp as well (I think it was called the X2000). These amps were designed to be used in that setup. In bridged mode, these behemoths produce a lot more power (and cost a lot more, too).
Many amps can do this. Bridged, common ground amps have their output stages, in effect, connected in series, not parallel as the OP suggested., thanks for the correction. Should have looked it up before posting.
Okay if someone bi-amps and has only one amplifier on, wouldn't that do the same thing as having two amps from different sources into one speaker pair as this thread addresses?

If not, then why? If so, then why don't more bi-ampers have damaged amps?
"Even in cases where someone bi-amps in a single system, there are two amps driving the speaker which in many/most cases is connected internally via crossover - regardless of how many binding posts are on the speaker."

I don't think anything's "connected internally via crossover" for a system designed for bi-amping: such designs use parallel crossovers (aka electrical filters): each driver has its own filter. It would only be a problem for series crossovers, but they are much, much, much less seldom used and no designer would put another set of binding posts on such a system. I believe.
This is why you remove the jumpers when you biamp: so they're not connected anymore.
do not do not do not do not
try this without a switchbox
Never, I repeat, never hook up one set of speakers, or one speaker for that matter,to more than one amplifier! It is very dangerous. You will blow out the amps. Theoretically it could be done with an A-B switch, however I don't recommend it. 51derrill
Well when I tried it, many long years ago, I blew up an amp when I forgot to make sure the other one was off. I presently have two systems connected to one set of speakers, so to speak, and I use a seperate set of cables to each amp. I use bananas at the speakers - I simply connect only the system I want to use by changing out the bananas to the appropriate amp. Simple and fool proof.