Okay well, just as a counterpoint to the pro fuse movement...
There is no scientific reason why swapping fuses should make a difference. You are replacing a 20mm piece of wire with a different 20mm piece of wire in series with a transformer primary winding that is many, many times longer than that. Being on the primary side of the mains transformer, the fuse is about as far out of the amplifier signal path as can be possible. The claims by Synergistic Research reek of pseudoscience. This particular section of their FAQ is particularly alarming.
"Q: Are fuses directional?
A: Yes, fuses are directional. Electricity should flow from the left to the right when you view the fuse. If you do not know the direction of flow you should listen to the fuse inserted in both directions. One direction will sound more detailed. This is the correct way."
These fuses are being used for alternating current, which is NOT directional, the flow of electrons reverses direction entirely 60 times per second dependent on the polarity of the AC waveform. This indicates the creator lacks a fundamental understanding of how electricity works, so I am more than a little skeptical of their "Inductive Quantum Coupling" technology. If you don't understand alternating current, you sure as heck aren't going to be able to understand quantum mechanics. Also, the Purple fuse is actually a modified normal fuse made by SIBA, which costs around $1.
Obviously, I am a big tube guy, I am not a measurebator. However, to design and build audio gear you do need to use science, measurements, etc. They do matter! I try to find a healthy balance between following the science and using my ears for audible things that the measurements cannot easily explain. But the fuse thing falls very far outside of my comfort zone as far as following the science goes. I gave it a fair shake and tried it myself, both sighted and blind A-B testing, and I could not discern a difference. I even fell victim to expectation bias at one point, which was later proven to be false by blind testing. Expectation bias can be very powerful, you'd be shocked by what you think you are hearing if you blind test.
https://www.head-fi.org/threads/l0rdgwyns-diy-audio.921105/post-17220095
https://www.head-fi.org/threads/l0rdgwyns-diy-audio.921105/page-371#post-17221162
I'm not saying people should be blind testing everything like they do over at ASR, but when it comes to something that really has no scientific explanation and you are paying 200x or more the cost of a normal fuse, I think it is worth trying. I know people don't like to hear that, everyone wants to "trust their ears", but we are talking about an area where there is a high risk of being taken advantage of based on expectation bias and the verbiage used on Synergistic Research's page is highly suspicious.
YMMV of course and people can do as they please. I've been more restrained on this topic in the past, but I think the alternative viewpoint should be given some consideration before everyone starts buying $200+ fuses.
