No fuses in gainclones?

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MtBiker said:
Secondary fuses between the transformer's secondaries and the diode bridges, or after the bridges on each rail?

I've seen both. I have one on the AC mains and two after the PS board on the +V and -V rails... reasoning is that I'm protecting my amplifier boards from my PS just in case something shorts near the opamps. (Perhaps not a problem in most cases, but my PS can do 15A at 31V on paper and I'd rather not take the chance.)
 
best fuse is no fuse at all. Ceramic fuse 'mellows' the sound, but silver fuse can make the sound 'thin':bawling: :D :D :D hehehe...

Not using fuse is breaking the law from another point of view. I just use the fuse in the 3-pin plug for protection purpose. I didnt use secondary fuse for cost and simplicity reason. But if your chip is the last piece you have on earth, you better use it.
 
Here's what I have gathered over the years regarding secondary winding protection on transformers...

On US machinery, it is was uncommon to see secondary fuses 20 years ago. Typically, that fuse will not protect the transformer in a short condition and it was thought that the secondary windings are going to burn anyhow. I am guessing that it was not a NEC (National Electric Code) requirement. Secondary protection may have been a requirement of the more stringent NFPA (National Fire Protection Association) or city codes like Los Angeles and Port of Portland among others.

Over the last couple decades, European machinery (and particularly machines complying to CE safety requirements) were either fused or OL breaker equiped on the secondaries. It's interesting to note that the CE standard control voltage is 24VDC compared to US standards of 110VAC.

So it is a world market, and we see secondary protection as standard construction feature on most industrial equipment today.

I have not used secondary protection on my GC's. Don't know if I'm right or wrong, it's just my observations.

If somebody has NEC 2005, I'm all ears.

My 2 cents.
 
If I use fuses on the secondaries, what would happen if I blow a fuse on only one of the rails?
Would that generate a full rail voltage across the speaker from the remaining rail, or would the chip protection prevent that?
I'd rather protect my very expensive speakers first, and the cheap chipamp second.
 
runer said:
If I use fuses on the secondaries, what would happen if I blow a fuse on only one of the rails?
Would that generate a full rail voltage across the speaker from the remaining rail, or would the chip protection prevent that?
I'd rather protect my very expensive speakers first, and the cheap chipamp second.

Even with one rail missing, there will be no DC offset at the output. The circuit will not be damaged either.

Happened to me at least two times.

Without the load, the circuit will show DC offset (with one rail missing), in presence of the load the offset disappears. You can experiment with it using 8 ohm power resistor instead of a speaker.
 
What fuse ratings for primary and secondary?

I have read the posts in this listing and conclude 1 primary and 2 secondary fuses are a good way to go for the brian gt lm3875 rev3.

What rating is appropriate (using a 330va avex toroid) for:

a) primary
b) each of the secondaries


For a 3 prong plug 110vac, where does the center ground connection go? This is for a wood enclosure.

Does polarity matter for the other two 110vac leads? No difference on the primary connectino for these, right?
 
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