Fuse direction for Pass amp and preamp

I am going to re fuse my Pass X250.8 and XP-32 with Synergistic Research purple fuses in a couple of days. I was hoping to get advice on a rule of thumb for direction of the fuses. My instinct tells me to start by installing the fuse by the direction of the lettering on the fuses. I am thinking that the direction should be the lettering left to right with the beginning of the lettering facing out of the amp and the end of the lettering facing into the amp. Does this sound right?

I will be re fusing 4 components at the same time so a good rule of thumb is important. I will be refusing my Pass Labs X250.8 and XP-32 as well as a new PST transport and an Auralic Aries G2.1 streamer.

According to the Synergistic Research web site:

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.

In a typical amp or other component with the fuse holder being in between the iec inlet and power on/off switch would it be proper to put the fuse in with the lettering on the fuse left to right with the end of the lettering to the inside of the amp or component and the beginning of the lettering to the outside direction of the amp? I will be doing 4 components at the same time so it would be reassuring if there is a rule of thumb.

Happy cake day!


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Thank you for both the well wish and the photograph which diagrams everything and addresses the OP question very well.

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I’d always do a continuity testing to find out, as every fuse holder can be connected differently. Just in case those pictures are from the manufacturer of the equipment asked for, they make sense imo.

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Makes sense :+1:t2:

So I have 4 components I will be changing fuses in. Should I do one at a time or do all 4 but start switching one at a time to hear for difference?

I would do the latter. I love a big barrage of audio change. :wink:


If you’re curious about the influence of the fuse on the sound of each component, I would do one at a time.
Curiously, I heard no difference with my XP-30, the predecessor to your (sublime) XP-32.
My XA100.5s have circuit breakers, so that solves that!
Don’t be in a hurry. One at a time.

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Which is an interesting concept to ponder when we are discussing alternating current. What exactly does direction mean in an AC circuit. Inquiring minds wish to know.


I second Paul’s confusion. See typical full wave rectifier schematic below as found in most audio gear. If the fuse is ahead of the rectifier (most typical) the current will definitely switch directions every 16.7ms. How can the fuse be directional?

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Try asking a fuse mfr for an explanation. I have. “It just is” is the answer I got from Synergistic.

Let me start by reiterating something I wrote in another thread and that’s the fact you could fit what I know about things electrical into a thimble.

That having been said, some of us (a) hear differences between different fuses and (b) among those who fall into point (a) some/most of us hear a further difference depending on which way the fuse is oriented.

Going back to my thimbleful of knowledge I’d guess it has nothing to do with alternating current but rather it has to do with how fuses are manufactured. This is just a guess on my part because some of us do hear differences. I know this is a far from satisfactory/definitive answer – it’s just an attempt to explain what we hear.

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The electromagnetic wave is in one direction from source to load.

I did them in batches. In my case the ones that impacted music the most were replacements in linear power supplies and the power plant, then source components, then power amp. Also, In the case of the cartridge type holder, I found they sound best with arrow moving back to front (contrary to wiring convention) irrespective of where the gear was manufactured!

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Fuse directionality has been discussed ad nauseam on this in the past, particularly with the use of SR fuses in PSA products. Given that these fuses have “directionality” and is from S to R according to the manufacturer, and PSA says current flows from cap holder to unit, then the fuse should be placed with the “S”
in cap, and the “R” resting first in the unit. I have done this with Blue, Orange, and Purple sets, and for me, sounds best. I might add, however, my listening was done a while back and it was a subtle, if any, difference.
I get that all this may be counterintuitive as AC is bi-directional and SR may not be consistent in their manufacturing but this is the best I got. A foolish consistency might be better than nothin.


Put in simpler terms…one direction gives more detail liveness,
the other direction gives a warmer, fuller sound…with less quickness
and detail.

The choice then becomes which type of sound
characteristics most please you…

Again it is how we appreciate what we are hearing.

Hope this helps
Best wishes

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David, that’s my experience as well. My system likes a mix of the two “flavors” . . . .