??? Fuse UpGrade??What Size???

As per 240i manual, page 25; you need a large AG Size (6.3x32mm) Fast Blow - 4 Amp fuse.

Sweet..I did not know the AG designation related to the physical size..Thanks much..

@freediver keep us updated on the outcome.  I would be interested if you notice any difference.  I swapped in a Purple Fuse and did notice improvement, wasn’t night and day but there seemed to be a wider deeper soundstage and improved imaging.  Could all be in my head but I don’t think so.

@jastralfu ,WilCo...

Let it burn in for a week and then switch the direction. If it wasn't in the optimal direction, you should hear a very noticeable difference. If it gets worse, well switch it back. I tend to oversize the fuse... thicker wire. 

Go with a 6 amp fuse Fast blow. SR fuses had a history of blowing on inrush current startup if you went with factory size. 

The Cable Company has them on sale.  

I would call SimAudio (Moon) tech support to get their opinion/advice.  I've received helpful advice from them on my Moon 390 set-up.

One is 20 mm ,one is 32 mm, you can see if it looks small or longer

and if fast blow always go 1 size up I have had fuses go in fast blow fuses on startup why ? The cheap stock fuses can vary up to 20%  

I recently upgraded my fuses for my Shindo Mr T,Aqua LinQ transporter and Weiss 501 MK2 for the Pink fuses and after experimenting with the right direction and between 100-200 burn in time,I can hear a very noticeable difference with the soundstage(,wider and higher),Instrments and voices are more detailed and airy and the overall sound is more live. I also recently bought a Rel S510 sub and Wow! It was probably my biggest upgrade. I know adding a second sub would complete the 20% on the 80 % upgrade but I live in a condo with neighbours downstairs so 1 is satisfying for me, should have done this years ago.

IME the Vera-Fi Audio SDFB outperforms any aftermarket fuse on the market. Many excellent reviews here & elsewhere. Email Mark with any questions. He's very responsive. 

I can vouch for the Synergistic fuses, I was skeptical, put one orange in my amp... Then I had to do every fuse, my preamp, my DAC, my streamer now all have SR fuses. Some really good snake oil that adds warmth, analog, real sounding performance value.

Now for the rest of my life I'll have to always buy these things because I couldn't have a 50¢ cheap fuse be the weak link in any component going forward... 

I'd use a pure copper penny to get the best sound. Pre 1982. (pssst, fuses make ZERO) difference in sound).

Can a McIntosh 2301 Mono amplifier fuse be upgraded?

@emergingsoul -

     There’s a fuse holder, next to the 2301’s IEC PC socket, on the top/rear of that amp.

                            Yes: that fuse can be easily upgraded.

     Two fuses also reside on a Printed Circuit board, within the amp.

      Those are harder to get to and you'd have to experiment with them, as regards any sonic benefit.

                                               Happy listening!

Fuses are important. I wouldn't vary from factory spec. 

Does anyone seriously believe that the makers of high-end amps or whatever would cheap-out on the freaking fuses knowing that by doing so they would be seriously diminishing the sound quality of a product that they had spent countless hours developing and testing? These fuses are an insult to common sense. BTW, I heard that by painting the purple fuse red you double the width of your soundstage. Geez.

No one is suggesting they cheaped out but that doesn’t mean there isn’t one that might be better.  Same goes for crossovers components in speakers.

     "Louis Pasteur's theory of germs is ridiculous fiction."  (Pierre Pachet, Professor of Physiology at Toulouse , 1872) 

     "The abdomen, the chest, and the brain will forever be shut from the intrusion of the wise and humane surgeon,"  (Sir John Eric Ericksen, British surgeon, appointed Surgeon-Extraordinary to Queen Victoria 1873)

      "The super computer is technologically impossible.  It would take all of the water that flows over Niagara Falls to cool the heat generated by the number of vacuum tubes required." (Professor of Electrical Engineering, New York University)                        

      "There is no likelihood man can ever tap the power of the atom."  (Robert Millikan, Nobel Prize in Physics, 1923)

      "Man will never reach the moon regardless of all future scientific advances." (Dr. Lee DeForest, Father of Radio & Grandfather of Television)

      "Heavier-than-air flying machines are impossible!" (Lord Kelvin, president, Royal Society, 1895) 

      "The bomb will never go off.  I speak as an expert in explosives."  (Admiral William Leahy, re: US Atomic Bomb Project) 

      "These fuses are an insult to common sense."    (@wesheadley, Denyin'tology Disciple)

     When the steam locomotive came on the scene; the best (scientific) minds proclaimed, "The human body cannot survive speeds in excess of 35MPH."

      Until recently (21st Century); and the advent of the relatively new science of Fluid Dynamics, the best (scientific) minds involved in Aerodynamics, could not fathom how a bumblebee stays aloft. 

     Often; Science has to catch up with the facts/phenomena of Nature and/or, "reality" (our universe). 

     I haven't been in school since the 60's, but- at Case Institute of Technology; the Physics Prof always emphasized what we were studying was, "Electrical THEORY."  He strongly made a point of the fact that no one had yet actually observed electrons (how they behave on the quantum level) and that only some things can really be called, "LAWS." (ie: Ohm, Kirchoff, Faraday)   

                         PERHAPS: that's changed in recent years and I missed it?

+1 @jastralfu - simply a better part can yield better sonics

Hi Gregory,

          Thanks for your comment concerning a second Rel S510 subwoofer. I had bought 1 a couple of weeks ago and found a noticeable improvement in all aspects of my SQ. Was very concerned about my neighbours downstairs, but never got any complaints so sometimes overthinking can stop us from moving forward. I decided to call my dealer and he had one more left at an incredible good deal since I bought the other one. That 20% missing is subtle but there.There is more coherence between the music and instruments. I can say, it’s like I was waiting at the gate of heaven and now I stepped inside for good. Thanks, just thought to share my experience with you,🎼🎹🪕🎻
 

Well I received my Purple fuse yesterday from HiEnd-Electronics..Since someone recommended I not listen for at least 12 hours after installing, I waited until late last night,put the new one in,plugged in my headphones & left it running..A good 8 hour sleep,breakfast & a few chores & 12 hours passed..
 Spent the last 90 minutes listening to Classical music,especially my favorite classical instrument,the cello...Now,perhaps it's just psychoacoustic bias, or a subconscious justification for spending $140.00 on a fuse,but I swear instruments seem to have more physical size & weight to them...Piano soundboards seem almost visceral,as do cello's,with body resonance clearly more defined.. 
Whether or not there is an actual gain in performance of my amp I will never be able to prove but even if it is purely a psychoacoustic benifit I would say I have NO buyers remorse & look forward to seeing if there is further changes as I put more hours on the fuse...

@freediver Littlefuse and Bussman make the best fuses around IME. Just for fun, you might obtain some and then do the same listening test that you did in your post just above.

BTW running an overrated fuse is bad advice. If for any reason your equipment failed with an overrated fuse in it, even if the fuse was known by some to fail earlier than stated on the label, your warranty would be void. If the fuse actually held to its rating, it could start a fire if there was a component failure.

@atmasphere I completely agree with the statement about running an over rated fuse,I stuck with factory spec'd size...