Signal degration over length, source vs. output ?

If you have a solid state preamp with output impedance in the 50-100 ohm range, interconnects are not all that critical. As Kr4 says, impedances for this interface (preamp to power amp) are well defined, whereas the power amp-to-speaker impedance relationship is variable. Therefore go with long interconnects. I note that at recording sessions it is not uncommon to have a hundred feet of interconnect wire between microphones the mic preamp and the recorder.

If you have a tube preamp, with the typical 600ohm output impedance, keep the interconnects short.

These general rules apply for "decent" (affordable)wire. The disadvantages of long wires of either type can be overcome (so they say) by various kinds of exotic wire configurations, for which you will pay dearly.

I have a tube preamp with <50ohm output impedance as well.

I agree with what El and Kr4 are saying in terms of low output impedances being highly beneficial to this situation, but El is tossing out statements about long mic cables while forgetting to mention that these are all primarily runs of balanced / xlr cables. BIG differences in performance between xlr's and rca's on a long run.

Corona: If music consisted of a series of non-distorted sinusoidal waveforms, your comments would make more sense. Since it is quite possible to have notes that are not of equal amplitude / duration in positive and negative attributes, "diametric opposition" or having an "AC flywheel" doesn't come into play quite as much or as linearly as one might think. Then again, i might be misinterpreting what you are saying as you tend to "fly" with your "cloaking devices" pretty well maxed out.

Having said that, I do agree with your comments pertaining to field contamination. I have tried to get this point across to Audioengr in terms of shielding of cables only being bad when it is improperly applied. You may / may not agree with this, but judging from what i think you're getting at, i think that you would agree. Sean
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speaking of 8...10' you loose almost nothing with longer speaker cables.

Kr4...I didn't know that you could get 50 ohms output impedance with a tube output stage (usually a 12AU7 cathode follower: 600ohms). What kind of preamp do you have, and did they slip in a transistor line driver?

sean...Yes: balanced lines are better for long runs, but that's another discussion. I only meant to suggest that a long run of low level signal is not the end of the world.