Fuses fuses fuses

ok dude!!

@zavato 
I tried to warn you...

are specialty fuses  supplied as original equipment, and directivity.

I don't fully understand the question you asked. 
Do you mean aftermarket fuses already installed by the manufacturer?
If so, I doubt any put them in as original equipment.
Bob

I don’t want to put words in Ralph’s mouth, either, but I’m pretty sure he’s not really on board the whole fuse directionality train. His argument is (and I suppose he could possibly be accused of fence sitting on fuse directionality) that when someone flips the fuse it somehow magically gets a better grip in the fuse holder. Cough, cough As I recall the other fence sitter Almarg agrees with Ralph in this regard.

Thanks, Geoff, that was what he said!

Actually that isn't what I said.

Its not magic.

Its the simple fact that neither the fuse nor the fuse holder have perfect dimensions. As a result, there is a small amount of resistance at the contacts as the fuse sits in the holder. If you shift the fuse around you can reduce or increase that resistance. That is why they **appear** to be directional.

Now this is easy to measure. All you need is a DVM (Digital VoltMeter) and you simply measure the voltage drop across the fuse in the circuit. Its not going to be very much, so a DVM with more than 3 1/2 digits is helpful but not mandatory. If the fuse is in an open holder, you simply rotate it in the holder and you can watch the voltage drop across the fuse rise and fall. The least voltage drop is what you want. 

Panel mount fuseholders are harder to deal with because you can't rotate the fuse while the device is on (and BTW, this is not for someone who does not have technical skills as you can zap yourself easily enough, so if any of this sounds weird or mysterious take the unit to a technician and have him do it) so quite often the remedy is to simply reverse the fuse in the holder. But you could spin it; the problem is with a panel mount holder its going to be random results. **That** is why it **appears** that there is a directionality!

So to be very clear this is only reducing the voltage drop of the fuse **in the holder**. Its not only audible its also easily measured.

An alternative is to use a better fuse. That is why we use FNM types with the larger fuseholders on our MA-2 amplifier. They put considerably greater pressure on the fuses, which have much larger (and usually silver-plated) contacts. Now we've been doing that since the inception of the MA-1 way back in 1990; that's how long we've been aware that fuses can be audible in the circuit.

I can't speak to the average fuse holder and fuse dimensions mentioned, but the ones in my Marantz Reference don't appear to be average.

They appear to be silver plated (not really sure)
They  have a shape that can only hold the fuse in one manner
They require effort to remove (the circuit board literally lifts upon removal)
They can be rotated in place but it is not easy to do so 
Comparatively, they have a much tighter grip than any bananas I've encountered with speaker cables and speaker terminals

These facts then to relegate the "what could be wrong with fuse holder" arguments to a fall back position: a general statement.

I readily concede that not all fuse holders are equal but that implies that some don't fall into the category of holders with poor contact points. It could very well be that Marantz takes all aspects of QC seriously and rejects lots of fuse holders or goes for a top grade vendor to supply them or even makes them themselves. I can't really say one way or the other but then, how often does this come up in discussion?

All the best,
Nonoise

So to be very clear this is only reducing the voltage drop of the fuse **in the holder**. Its not only audible its also easily measured.

To clarify this more, it "maybe" only audible if the supply stages after the fuse/holder are NOT regulated. Most sources, s/s preamps are so it shouldn't be audible .
Some power amps can be, most not. 

Cheers George