Unfocused Sound stage

I second Newbee's comment. The only things I can think of that would account for the symptoms the OP described are a +/- reversal to one (and only one) speaker, or use of a balanced interconnect that has pins 2 and 3 interchanged at one end of the cable in one (and only one) channel.

Regarding the experience Marakanetz reported, I agree with the comments by Stan and Metro, provided that the speaker is purely passive (i.e., it does not contain an amplifier), and provided that a powered sub is not connected to the outputs of the main amp.

If the main amp is connected to the inputs of another amp (either in the speakers or in a powered sub), then it is possible that a +/- reversal could cause damage. That would occur if both amplifiers have 3-prong power plugs, and both have ac safety ground in common with (i.e., connected to) their internal circuit ground. In that situation reversing + and - would short the + output of the main amp to its ground, via a path through the amp in the speaker or sub and the safety ground wiring of the two components.

Regards,
-- Al

I have never heard of swapping the plus and minus connections on a passive speaker cause any amp damage either. Like Almarg said, if the speaker is AC powered somehow, or a powered subwoofer that may tie the two plus or minus outputs from the amp, yes, that can cause damage. Regular passive, never heard of it, just as long as the left and right channels connections stay isolated from each other.

If this wide sound stage happened on its own, there may be a bad connection in a component, or one of its semiconductors somewhere. With the ground, or other connection opening somewhere, I think there is a possibility that it is starting to give the ambient information (the difference between the two channels) and acting like a matrix surround sound coming through your mains speaker.

Double check all of your speaker connections like mentioned.

If this is a vinyl system, double check your cartridge and turntable connections.

If you have any recording that you know that has an instrument, or vocal that comes *mostly* but not totally out of one channel before, try it and see if it still does. If it comes more out of both, possibly with some echo now, there is a good chance like I mentioned before about a bad connection somewhere in a component or outside (cartridge/speakers etc.) wiring. Another sign of something like this happening can be a lot of reverb/echo type of sound in a lot of your stereo music.

Figure seven in this link is something on the idea I'm picturing could be happening, somewhere in the system. Link
[http://www.amsky.com/~cirkuit/media/surround.html]