Safe to add a different than recommended fuse in equipment?


#1

Like the Directstream uses 5x20mm 1 amp slow blow fuses, but what if a 1.2 or 1.5 amp fuses was used instead?
Seems like a small difference, wouldn’t that be safe?

Would only going to a 2 amp or above not be recommended?

I also always wondered, but does a slow blow vs fast blow matter in the sound or safety usage? Like if the 1.2 amp slow blow fuse was replaced with a 1.2 amp fast blow. Does it have any other consequences other than the speed at which it blows?


#2

Safe is a relative term. If you replace a higher amp fuse, a 1a for a 1.2a, you run the risk that fuse won’t open when needed and the part that failed or shorted could heat up and cause a much larger safety issue, like a fire.

That said, if you’re looking to see if a fuse you have sounds better and it’s slightly uprated, you’ll be fine but I would determine if you like the sound and then purchase the correct fuse for permanent use.


#3

A larger value fuse is a bad idea.

The purpose of the fuse is to prevent overheating (component damage) or fire in the event of a fault on the load side of the fuse. The fuse rating is a function of the maximum acceptable component heating caused by fault-mode current.

A normal fuse blows immediately upon being subjected to a current greater than its rating. On the other hand, slow blow fuses will not blow in less than 5 seconds at 200% of its rating. Slow blow fuses thus allow for short-term current in-rush without blowing, but will blow if sufficient current continues to flow through the fuse, indicating a fault condition.

A larger normal fuse will blow fairly often as the component starts, but if it remains intact it will allow larger currents to flow into the load than desirable. (By the way, a 1.5 amp fuse instead of a 1A is not a small difference, it is 50% over spec. That is, 75 MPH instead of 50 MPH in a 50 MPH zone. You will get a ticket.)


#4

What’s the reasoning behind using the larger fuse? So it ‘sounds’ better? Because you have a 1.2 and don’t want to buy a 1.0?

Fuses are meant to protect the system in case of a fault where something shorts out downstream of the fuse. If there were no fuse there’d be a massive current draw that could lead to either a burned component or a fire that burns down the house. The wire cord leading to the fuse is designed to withstand the current needed to blow the fuse in case of a short-circuit fault. Ideally the wiring downstream of the fuse will handle this current spike as well. Adding a bigger fuse will put a bigger load on this wiring in the event of a fault.

Most fuses operate anywhere at 30% to 50% of their rating so they don’t blow at power-on during the inrush power transient. So there’s already reserve margin built into the fuse at the nominal rating. Adding more margin by using a bigger fuse won’t change things very much and may be bad in the rare event of a short-circuit fault.

If you have a slightly bigger fuse and if the original fuse blows, you can try the bigger fuse, but chances are that if it blew the first time it may blow again, so find out why it blew and fix that before putting in something bigger.

But if all this is for better sound, just get a fuse like the HiFi Tuning or similar brands that are designed to sound better below their nominal rating and still blow at the proper current to protect you from smoking the unit or burning the house down in case of a fault.


#5

Excellent point, if a fuse is repeatedly blowing fix the problem. Do not try a bigger fuse.


#6

Yeah I have a different brand of audiophile fuses from one of my other equipment & wanted to roll it in the DS, but it was rated at 1.2 amps. I don’t want to take any chances unless one one of the PS Audio engineers say it’s o.k.


#7

I suggest addressing this specific question to PS Audio support.


#8

That’s probably just fine with a 1.2 in a 1.0 application. But as Elk says, see if anyone at PS Audio can comment. If it were a 10 Amp I’d say no, but a 1.2 A . . .Don’t sweat it.


#9

I can say that it’s definitely a bad idea in the Jr and probably a bad idea in the Sr. As earlier responders said you are risking fire (among other things) A fuse’s life is hard enough when correctly sized but being oversized means they are much less likely to do what they are intended to do: protect your household.


#10

Even a 1.2 in a 1.0 application? That’s only 20% more margin, you’d think the wiring can handle that in the event of a short.


#11

Remember 0.2 amps at 120V is 4.8 amps at 5V… which is a lot more than the whole nominal draw on the supplies in the DS. (Not that the supplies are 100% efficient in the DS, they are far from it, but 0.2A at 120V is still 24W…)

I don’t know how often an internal fault causes a fuse to blow in DS’s, but not all faults are created equal. It’s easy when there’s a rail to rail short near the AC inlet, but the low voltage power supplies in the Jr and Sr can melt 16 gage wire without blowing a fuse or otherwise harming the power supply components (I know from unfortunate experience) so there can be bad things going on long before the fuse notices. Don’t make things even less likely to work well…