I live in 230V country and I have slightly larger filter caps and donuts compared to stock F5, but with a bit of luck, I can start it up with 2 A fuses. I use one NTC similar to CL-60 on the primary. Without the NTC, I blow 4 A fuses (2 A fuses literally explode).
If you hesitate when flicking on the power switch, the transients from the contact can heat up the NTC and result in blown fuses leading to periodical failures.
If you hesitate when flicking on the power switch, the transients from the contact can heat up the NTC and result in blown fuses leading to periodical failures.
I can recommend the Avondale Audio soft start.Been using one in my amps for several years now without any failures.Not cheap but does what it says on the tin.
Hmmm. I don't like the sound of that! I wonder if using incrementally larger fuses (up to a point) is a better solution.
I have 4x 18,000uF 50v on each rail, so not hugely excessive.
I have set current according to instructions, at 0.6v bias, but my rails are slightly higher hotter at 26v, due to the UK pretending to Europe to be 230v but actually clinging to 240v.
My speaker leads are Van Damme Studio Blue 2.5mm sq. with Speakon connectors (used as no current limiter on the amp - protects against accidental shorts). I don't think they're especially capacitative.
Ah, that's good to know! It makes a lot of sense, and kind of demonstrates the reality of component burn-in.
Perhaps I'll just set myself a 2.5A maximum limit and work with the process.
f5 blowing fuses.
4 x 18,000uf per rail is a lot of capacitance especially if it isn't a CRC filter arrangement. I have built several F5's either as monoblocks or stereo in the one box and have never used more than 4 x 10,000 per rail and there is always a resistor of about 0.1 ohm between the first 2 caps and the other 2 (each rail). The CRC arrangement gives a smoother ripple rather that a slightly triangulated wave which ensures practically no output hum. I've never had problems with fuses. Sounds like a soft start would help. Your speaker leads don't sound like a problem.
Regards, David.
4 x 18,000uf per rail is a lot of capacitance especially if it isn't a CRC filter arrangement. I have built several F5's either as monoblocks or stereo in the one box and have never used more than 4 x 10,000 per rail and there is always a resistor of about 0.1 ohm between the first 2 caps and the other 2 (each rail). The CRC arrangement gives a smoother ripple rather that a slightly triangulated wave which ensures practically no output hum. I've never had problems with fuses. Sounds like a soft start would help. Your speaker leads don't sound like a problem.
Regards, David.
I find it difficult to believe you have missed all the references to soft starting and close rated fusing and all the other references to normal transformer fuse rating when a soft start is not adopted.
Fuse value for a transformer or motor ~ THREE times the VA rating divided by the supply voltage.
For a 300VA the fuse required for long term reliable "no blow" start ups is 3.75A use either 3.15A or 4A.
If you adopt soft starting, then you can get away with T1.25A, if you select an appropriate current limiter value for close rated fusing.
Perhaps I should have mentioned - mine is a CRC:
36,000uF / 0.12R / 36,000uF per rail.
Thanks for your advice.
Ahhhhhhh! Now that's useful! The First Watt General Power Supply simply states that it must be a 1.25A fuse, and no other information is given.
I will use a 3.15A fuse and hopefully be done with it, as the amp is silent and works perfectly in all other regards. Many thanks.
How much current will that 3.15A fuse pass without blowing for say 30minutes while you are at the front door trying to persuade some unwelcome caller they are not wanted?
I always recommend close rated fusing. That almost always requires adoption of soft start.
I always recommend close rated fusing. That almost always requires adoption of soft start.
Are you suggesting that 3.15A will not protect anything in the event of a surge, for example, by being too nail-like?
NP is putting CL60 as soft start in his commercial products , meant to be both bullet and idiot proof as much they can ;
is that something telling to you ?
with one CL60 in line , I'm using T4A on 800VA Donut , combined with 8x33mF , in one of my amps , on 220Vac line
never had fuse failure , even in case of black-out ( worst case scenario for sole NTC based soft start)
is that something telling to you ?
with one CL60 in line , I'm using T4A on 800VA Donut , combined with 8x33mF , in one of my amps , on 220Vac line
never had fuse failure , even in case of black-out ( worst case scenario for sole NTC based soft start)
But all seems to be solved by simply adding the higher value fuse. Why complicate things? My amp has nowhere near your huge transformer, or capacitance, and I have a smaller fuse, and all is well.
The 3.15A fuse should stop the cable feeding a faulty F5 from setting fire to the house.
I don't like that. That's why I prefer close rated fusing.
I don't like that. That's why I prefer close rated fusing.
Hi guys...a question on a different topic.
What is the lowest input impedance the F5 can have and still operate properly? Typically it is either 100k or 50k....what about 1k???
Don't be concerned about the pre-amp having to drive the 1k load....Just consider the F5 here.
What is the lowest input impedance the F5 can have and still operate properly? Typically it is either 100k or 50k....what about 1k???
Don't be concerned about the pre-amp having to drive the 1k load....Just consider the F5 here.
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