The test is really simple: feed the exact same mono signal to your monoblock amplifiers, with and without different fuses (thus, keeping everything else constant) by replacing one fuse at a time, to easily look for differences; if your speakers are properly positioned in the room and you have no weird room reflections, no differences using a mono input signal would be rendered as a perfectly stable mono image right down the middle between the speakers as you move your head around, as you would expect; but if there are differences, you will easily pick them up and then you engage in critical listening to figure out whether they are for the better or worse. This is your typical equilibrium-type test, where you bring the system to equilibrium, change one parameter and see if it makes a difference, then bring it back to equilibrium; if that one parameter change affects equilibrium, evaluate it further.
- In Stereo mode, set the preamp's volume at a constant, normal-to-high listening level for the duration of the test. Test with high-powered music.
- Replace the preamp's stock fuse with the same kind under evaluation - this eliminates the preamp's fuse from being the weakest link in the experiment. Remember, fuses _may_ make a difference depending on how your entire system draws current (in the case of Spectral, probably how this affects the leading edge) - the fuse is an integral part of the critical power supply. Wait for the preamp to warm up again as long as you see fit. When I did this step I heard no differences, but I suspect it was eventually because the weakest link at that point were actually the amplifiers' stock fuses. If you do hear differences, then steps 3-5 are probably less necessary but still worth doing.
- Still using the stock amplifier fuses, now push Mono on the preamp; as you move your head around the mono image should remain completely stable and dead center. This proves that the amplifiers reproduce the exact same input signal exactly the same way with the stock fuses.
- Replace one of the amplifiers' fuses with the new one under evaluation; you are still in Mono; wait for the amp to warm up again as long as you see fit; move your head around and see if the image is still completely stable and dead center, or whether there are differences; this is really black and white. In my case, the image changed and moved slightly as I moved my head. If there are differences, this proves that the amplifiers now reproduce the exact same input signal differently, and the only parameter changed was one amplifier fuse.
- Replace the other amplifier's stock fuse with the new one under evaluation; you are still in Mono, and now both amps use the same [new] fuses, as well as the preamp; if you heard differences in Step 4, the image should now be completely stable again. This proves that the amplifiers once again reproduce the exact same input signal exactly the same way but using the new fuses, verifying that you did indeed hear differences in step 4. You can repeat 3, 4 and 5 as many times as you want to convince yourself.
- Steps 2 and/or 4 may have established differences: qualify them with critical listening in stereo. In my case, they were for the better, and quite evidently so. There can be a number of valid reasons why you may not hear any differences; e.g. your stock fuses are already very high quality; your system isn't necessarily fast enough and the leading edge is not affected by fuses; your system's power supplies sport high-capacity capacitor banks and they do not really need to draw a lot of current very quickly; the music you used for this test is not high-powered enough and does not stress the power supplies; etc...
Therefore, whether fuses make a difference in anyone's system or not is system dependent, and you just need to try them out. The better systems, of course, will require no fuses and employ sophisticated and non-intrusive monitoring and power-cut-off circuits.
