I have installed the HiFi Tuning Supreme fuses in my C1000C controller, MC2301 amps, and MC601 amps. I had to order another 500mA HiFi Tuning Supreme fuse for my C2300 because on my initial fuse order I neglected to notice the C1000C controller required two fuses, so I used the fuse I ordered for the C2300 as the second fuse in the C1000C.
The HiFi Tuning fuses have a symbol printed on the barrel with an arrow. I take this to be an indication of the direction the fuse should be installed in the 120 volt circuit. Initially, I installed the fuses with the arrow pointing into the amplifier. After several days of auditioning I decided to reverse the direction of the fuses, and surprisingly discovered the systems sound better with the fuse arrow pointing toward the rear of the amp. In other words, the fuse arrow is pointing toward the fuse holder cap. This discovery motivated me to pull my C1000C out of the rack, remove the cover and examine the fuse holder. As I suspected, the voltage path through the fuse holder is toward the rear of the amp. See my example below.
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This particular fuse holder wiring scheme is the way McIntosh routes the incoming 120 volts AC. I cannot state with conviction that this is how other manufacturers may wire their fuse holders, so you should look for yourself if you plan to install HiFi Tuning fuses in amplifiers or preamplifiers other than McIntosh.
With respect to the sound of my gear after the HiFi Tuning Supreme fuses were installed in the correct direction, I am sensing a minor improvement in the micro details, plus a small improvement in the space between voices and instruments. This improvement is not dramatic, in my opinion, more just a slight increase in clarity of the presentation. This did not jell until I reversed the fuse positions from my initial install, and though I don't understand why the direction of a fuse impacts the sound, I sense the system sounds better with the present fuse arrangement. At $53.95 per fuse for the HiFi Tuning Supreme fuse in small Slo-Blo size, the four I installed in the studio system ran $215.80. As audio tweaks go, this is not an outrageous price, even considering the audible improvements aren't monumental, at least to my ears. I had the same sensation of a slight performance enhancement with the MC601's in the living room system, and feel that once my last HiFi Tuning Supreme fuse is installed in my C2300 the overall performance bump is worth the price of admission.