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Old 23rd November 2002, 05:11 PM   #1
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Question fuse

i have a DJ amp 800W X1 (4 Ohm) (8 tr' of 2SC5198-2Sa1941)
in my amp dont have a fuse or protection...
i want to put a fuse for protection.... how much (A) fuse i needed for speaker out??
and how much (A) fuse i needed for power supply in my amp??
(48V AC 600VA)
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Old 23rd November 2002, 05:21 PM   #2
trwh is offline trwh  United Kingdom
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Hi DJ

To calculate the correct speaker fuse value, we can use the equation P = I^2*R, which is rearranged to I = sqrt(P/R). Thus, a 800W 4 ohm speaker should draw an RMS current of about 14.1A. A 15-18A speaker line fuse would therefore be suitable.

For a symmetrical 48V supply with a 600VA transformer, ignoring any rectifier losses, a maximum current of about 6.25A per rail can be supplied. A 6.3A slow blow fuse in each rail would be about right - maybe a 10A if you experience any nuisance blowing. Make sure you place the fuse in the supply line _after_ the reservoir capacitors.

As a side note, the fact that your "800W" amp only has a 600VA transformer and absolutely no output protection, shows it is a poor design. Like I say, consider proper PA equipment next time.

Hope I've answered your query,
Tim.
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Old 23rd November 2002, 05:29 PM   #3
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can i make him stronger....?
change the transformer to 50V AC 800VA
change the tr' (2SC5198-2SA1941) to 2SC5200-2SA1943
??

(i build this amp...)
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Old 23rd November 2002, 05:33 PM   #4
trwh is offline trwh  United Kingdom
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"can i make him stronger....?"

Not easily. The whole design must be considered, you cannot just increase the capacity of the transformer and change the output transistors. If you need more power I wouldn't waste time and money on this amp - try a different design.

Tim.
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Old 23rd November 2002, 05:44 PM   #5
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i have a lot of strongs Dj Amplifiers...
of GEMINI
and PYRAMID (bad amp) and NUMARK AMPS...
for my dj...

but i want to build a amp...
soo can i shange the part in my amp to make him stronger?
the money is not a problem...
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Old 23rd November 2002, 05:47 PM   #6
jleaman is offline jleaman  Belgium
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dj bass amp if you want raw nice out put power and you want tobuild it i would go witha pair of av800's from www.aussieamplifiers.com i ordered my boards and wow they look nice. it might cost ya a few pennies but hey youll have TONS of crisp clean and reliable power.

like me..: O )
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Old 23rd November 2002, 05:51 PM   #7
dhaen is offline dhaen  Europe
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Generally "silicon fuses" blow faster than real fuses.
When the real fuses blow, it's often too late.

BTW: I'm not saying don't use them - just an observation!
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Old 23rd November 2002, 05:53 PM   #8
trwh is offline trwh  United Kingdom
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"soo can i shange the part in my amp to make him stronger?"

No. Not just the transformers and transistors.

"but i want to build a amp..."

The "double barrelled" Leach amp would be a good choice, or maybe one of the designs from www.aussieamplifiers.com.

Tim.
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Old 23rd November 2002, 05:54 PM   #9
trwh is offline trwh  United Kingdom
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Oops, sorry Jason, I was writing my post while you suggested www.aussieamplifiers.com!
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