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Old 19th February 2009, 08:52 AM   #1111
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Default Fuse blow

Me... again.

My stereo VSPS is working fine, but in a couple of days three fuses of the PSU blew at switch-on or off.
I use a 0.5A fuse as specified in the VSPS building guide but I don't know what type of fuse is: slow blow or fast blows (terms I read in this thread). The transformer is a toroidal 80VA 2x12VAC (230VAC primaries).
I suspect that it is a problem of inrush current at switch on, because once the PSU is on the VSPS is working fine. Moreover the fuses do not blow when I use the light bulb tester which I read also acts as a soft starter. You know I am a newbie, but if I apply the Ohm Law, at full power I get 0.35A current at IEC plug, so 0.5A could be a not sufficient margin at switch on.

Do you think I can increase the value of the fuse, could be more serious problems or do I need a soft starter to avoid damage of the VSPS circuit?

Thank you again for your patience


Renato
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Old 19th February 2009, 09:24 AM   #1112
rambojj is offline rambojj  Germany
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what kind of fuse is it? Think, when you switch on the psu the transformer has a hight current and you need a T-Fuse.
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Old 19th February 2009, 09:39 AM   #1113
rjm is offline rjm  Japan
Richard Murdey
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The fuse is connected on the 230V line right? Just checking the obvious first...

A 0.5 A fuse limits the power to 115 Watts. In my view if the VSPS is drawing more than 115 Watts it's time to shut things down, so I don't really recommend increasing the value.

You almost certainly are using a fast fuse. You need to use a slow-blow or SB type fuse that will not trip on the inrush transients.
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Old 19th February 2009, 10:16 AM   #1114
AndrewT is offline AndrewT  Scotland
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Hi,
an 80VA 240Vac toroid will need a T1A mains fuse to start reliably without nuisance blowing. This is a guide figure, it may be that this particular transformer could use/need T800mA or T1.2A

If you want to close rate the mains fuse then consider a soft start.

BTW,
a T1A will pass 2Aac for quite a long time before it finally ruptures.
What damage to your household could that 480W of misused power be doing in the meantime?
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regards Andrew T.
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Old 19th February 2009, 11:07 AM   #1115
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My DIY lm1875 chipamp with a 225VA transformer is working fine with a 1.6A fuse.

By specification the main fuse of my home blows for power use grater than 3KW at 230VAC. It happens when I switch on the washing machine forgetting that the electrical oven is already on!

Renato
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Old 19th February 2009, 04:41 PM   #1116
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Default Fuse blow

The fuse in my VSPS PSU was F0.5A (fast blow).

I replaced it with with a T0.630A (slow blow); I switched on/off 10 times the PSU
without fuse blow.

Thanks to your help I learned how to recognize a fuse, how to get a guess of circuit current, how...


Thank you again, your help is unvaluable


Renato
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Old 8th March 2009, 10:47 AM   #1117
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Hi, a couple of questions. How small could I go on the output caps? I've got some nice 1uf plastic ones I'd like to use. Also, the riaa caps I want to use are .0033 instead of .003. Would this value skew the eq to much? Thanks
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Old 8th March 2009, 01:09 PM   #1118
rjm is offline rjm  Japan
Richard Murdey
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3.3nF is 10% off the correct value. Normally you'd try to keep everything within 3-5%.

1uF is most likely OK if the following stage has a highish input impedance. Worse case is a bit less bass response. You can always connect two 1uF caps in parallel if you find out later that its an issue.
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Old 9th March 2009, 12:07 PM   #1119
rambojj is offline rambojj  Germany
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Default value Rin

Last week I got a new tone arm wiring. He (the man who changes the wire) gave me the advice to change the Rin from 47 kOhm to 100 kOhm. Has anybody some experience with that value? And what about a cap at the input (my system is an Ortofon OM 40 super MM cardrige at Rega RB 300 with the Funk Firm Vektor TT)
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Old 9th March 2009, 01:10 PM   #1120
ahaja is offline ahaja  Poland
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Hello
This is interesting about R loading:
http://www.vinylengine.com/phpBB2/vi...t=6674&start=0

Regards K
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