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The designer of my amp, not me, says it is ok to use a 3.75 fast blow fuse in an amp that came with a 2A fast blow fuse. The spec says a consumption of 60 watts. 60w/120volts = .5 amps. If this is correct both 2 and 3.75a fuses seem high??? Is this math correct? If correct then why would an electronics designer ( I'm pretty sure) say the 3.75 is ok? Thanks, Tweaker
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is not an indication of the max power consumption that the sum total of the circuit and all its parts can safely tolerate. In other words, your calculation is not helpful. If the person you consulted is really the designer, then you probably can trust his judgement.
The reason it's ok to use that high of fuse is due to inrush current on power up. there is a current draw due the caps in the power supply charging up. If the fuse was too small they would blow constantly upon power up.I have a power amp that puts out 175 watts but has a huge Transformer 1.5kVa with cap values of 33,000 each. so the current draw is huge so my original fuse was a 6A slow blow. The guy that who helped design my amp says I could use fuses that were a little higher 8A. But since the fuse never pops on power up with the original value I just left it alone.
When the fuse did blow it was due to a problem and it turned out to be a bad capacitor. So the fuse was perfect in value.
I went to a ceramic fuse and I did notice an improvement in sound. I switched the original fuse and the ceramic fuse in and out a few times with the ceramic fuse making my system better sounding by a good amount.
Edits: 05/05/16 05/05/16
Cougar, A bad cap blowing a fuse does not define what a perfect fuse would be. Lots of things can blow a fuse. One major consideration is the weakest link current capacity wise as someone here recently pointed out and can be read about when reading on the subject of fuse selection and safety. If in fact an 8A fuse is justifiable safe in your amp I would run to the nearest fuse store, replace the 6A fuse with the 8 and marvel at the improvement in sound and how lucky you are to even have an amp that can take a 6 or 8 amp slow blow fuse safely. That in and of itself gives your amp an advantage that many lack from the get go. Tweaker
that value was good and it did what it was supposed to do when the cap had an issue and protected the rest of the components or amp from further damage. There are other ways to make an amp sound better with power cords, Caps, Resistors, internal wiring and list goes on.
Amps mostly come with 2 types of fuses fast blow for the power rails and slow blow for the power supply when amp is powered up due to the large current draw on power up. Most amps also have what are called NTC that limit inrush current with High resistance at first power up and when the part starts to warm up the resistance goes down to a very low resistance. This helps give the power amp a soft start on power up that help reduce strain on the Bridge Diode and caps. Then there are some amps that have Fast blow fuses on the outputs.
I did try the 8A and there was no noticeable difference in sound in my system. But for safety reasons I keep the lower fuse in as it doesn't hurt anything and which blow faster than a 8A fuse if something does go wrong without taking out other components. Which I explained above.
"Why question it". #1 The amp came with a 2A fast blo fuse and didn't pop on turn on surge. #2 IMHO a fuse almost twice as large sounds much better. So why would someone trying to sell amps degrade the sound with a small fuse? #3 At 60 watts consumption the amp draws aprox. 1/2 amp. A 2 amp fuse is 4 times its likely max. running current. #4 An amp designer and tech said no way a 3.75A fuse is appropriate in this situation when I discussed this with him. Tweaker
Inrush current on power up I guess.
ET
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