Using fuses on VDC Power Supply Rail? - diyAudio
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Old 22nd December 2002, 11:04 AM   #1
Lucas_G is offline Lucas_G  Netherlands
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Join Date: Nov 2002
Location: Netherlands
Default Using fuses on VDC Power Supply Rail?

Dear Aleph-builders,

I am building a pair of Aleph 5 and a pair of Aleph 4 Monoblocks.

I have found a wealth of valuable information on this forum.

However I still have one question left:

Most designers of other amplifiers prefer a pair of fuses on the VDC powersupply rails, because they think it is safer in case of malfunctioning since the fuse before the transformer doesn't alsways protect against heat/fire when something goes wrong after the transformer.

My questions are:

1. Do the Aleph designs need them? Does Nelson Pass use them? If not why?

2. Could there be any negative influence on sound-quality when using fuses? Has anybody done comparisons here?

3. Any idea what type of fuses to use in Aleph 5 or Aleph 4 (how many Amperes, slow or fast?).

Thanks alot for any info, and the best wishes for the New Year from a rainy Holland...

Lucas.
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Old 22nd December 2002, 01:50 PM   #2
fcel is offline fcel  United States
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Join Date: Sep 2001
Location: LA County
1. NP has mentioned many times on this thread that there are almost no failures on any of the Aleph amps that comes out from Pass Labs during the last 10 years.
2. If I'm not mistaken, the commercial Aleph amps only has one line fuse.
3. Didn't the owner manual also says that the amp will not be damaged even under a dead short?
4. I have originally intended to install a protection circuit board on my Aleph 2 but after listening to it for a couple months, I have decided against it.
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Old 22nd December 2002, 02:13 PM   #3
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Location: Columbia, SC
When I built my first pair of Aleph 2s, I was fiddling with the prototype on the bench. (This was before it was common practice to build Alephs. I think Mark Finnis and I were the only people attempting it at the time.) I was playing with various resistor values here and there, seeing how the circuit reacted. Since I was doing things that weren't sanctioned by the Pass folks, I reached over (without thinking it through), grabbed a couple of fuse holders, and stuck them in the rails.
Sure enough, I overdid it and popped one of the rail fuses. The current source promptly and enthusiastically dumped all that wonderful DC bias current through the voice coil of my test driver, thereby releasing the smoke that the factory had so carefully installed within.
Hindsight is a marvelous thing.
Moral of the story: No rail fuses for Alephs.

Grey
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Old 22nd December 2002, 02:32 PM   #4
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Location: Salt Lake City
Gray,
Thats exactly the conclusion I came to....no fuses except for the main line fuse. Fuses could never react quick enough to keep damage from happening to any of the devices anyway. Devices are damaged in microseconds, or sooner......but it takes milliseconds or longer for a fuse to pop.

BGW did have a system that worked most of the time on the older amps they built. Known as a "Crowbar" circuit. It sensed any DC on the output and the "Crowbar" circuit tripped the circuit breaker, or blew the main fuse. It actually was quite effective most of the time...but those were all Quasi type circuits with bi-polar output devices too.
Mark
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Old 22nd December 2002, 09:37 PM   #5
Lucas_G is offline Lucas_G  Netherlands
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Join Date: Nov 2002
Location: Netherlands
That settles it: I won't use any fuses on the output of the power-supply. (Is cheaper anyway... )

Thanks for your opinion!
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