Which SR Blue or black Fuse

@glupson

In my case the blown fuse was a little bit of user error as well as a little manufacturer error.  I was listening pretty loud when I switched on the fly from the triode to UL, instantly doubling the watts.  Later in discussing with the manufacturer, they recommended using a 4 amp fuse instead of the 3 amp fuse that came with the amp stating that you can usually get away with a 3 amp fuse but switching surges can sometimes pop the 3 amp.  Since then I always reduce the volume when switching from triode to UL and have never had a problem since, even with a 3 amp fuse.

I never had a fuse blow in all my years in this hobby. 

All the best,
Nonoise

@mrdecibel

I understand you’re a bit weak on electronics theory, but I’ll try to explain.

Like I said above, my amp uses very simple in-rush current limiting. In-rush current is the amount of power the amp draws when you turn it on. My amp uses nothing more than a pair of NTC CL60 thermistors to limit the in-rush. Once they’re warm they do nothing. You want to limit that because it can be a lot more power than the amp operates at. The in-rush is also very hard on rectifiers and the reservoir caps. My amp is a class A amp so it’s drawing all the power it will ever use just sitting there idling. It makes a lot of sense to fuse it as conservatively as possible to avoid damaging something more pricey that a 20 cent fuse. So... It’s not that it’s broken or poorly designed. It’s artfully simple in it’s design, as all Pass amps are. You want a fuse to be as close to popping as possible under normal use. The fact mine pop so easily indicates they’re well suited to doing their job.

So all that talk about other's poorly designed power supplies in their lousy amps and their boutique fuses was just a lot of hot air because you decided to build an amp that would often fail by design because you seem to think it sounds better that way?

You keep citing Nelson Pass's designs as the inspiration for yours and yet I've yet to hear of any fuses popping with regularity with his amps. If they did, we'd all hear about it by now and no one would be buying them.

Bartender, find out what he's drinking and order me a case! 😄

All the best,
Nonoise

@nonoise 

You're obviously not at all familiar with the First Watt products. You know... Like the J2 that got Stereophile's Amp of the Year award. Mine is a modified clone of the F5. The power supply in it is actually more muscular than what Nelson built the First Watt F5 with. The fuse pops at 300 watts like in all FW amps, but because mine runs 32V rails instead of 24V at the same 120,000uF reservoir capacitance, the in-rush current is a bit higher. All the First Watt amps will pop their fuses if you shut them off long enough to disconnect inputs then power them back on. It's just long enough to drain the PS caps, but not long enough to let the thermistors cool. 

I don't blame you for being clueless about FW amps. They're really nice amps for people looking for something different than you're typical idiot-proof production line amp. They're all hand built and adjusted by one guy; either Nelson Pass or the DIY'er who built it. Simplicity wins the day. No need for idiot-proofing here.