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Old 3rd May 2005, 07:25 AM   #1
Mark25 is offline Mark25  United Kingdom
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Question p3a seperate fuses for i/p, VAS o/p ??

All,
As it says in the subject tittle really, i want to seperatly fuse the 3 stages of my ESP p3a amp. So that the input stage and VAS fuses are not subject to the current drawn by the output stage. My audio experimentation thus far has indicated that this will improve sound quality. But the question is:

Are there any disadvantages in terms of loudspeaker life/protection?

i.e. would i be any worse of than the current situation, which is; if one supply rail fuse blows, the other rail will put X amount of DC on my expensive bass drive units.

Thanks Mark
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Old 3rd May 2005, 07:49 AM   #2
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What experiments have you condcuted to make you think this will improve sound quality?

It's a bad idea as if the output stage fuse blows, the driving circuitry will still be trying to drive the dead stage and you will get the output stuck at one of the rails (very nasty to your speakers). Purely theoretical this bit but, if you used MOSFETs as output devices you would also destroy them as their gates would be forced up to the rail voltage.
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Old 3rd May 2005, 10:49 AM   #3
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Quote:
Originally posted by richie00boy
What experiments have you condcuted to make you think this will improve sound quality?
going from stereo psu to dual mono, going from one bridge per split rail psu to one bridge per rail, separating or enlarging shared grounds in pre amp psu's, etc, etc. Basically anything that limits the sharing of resources, or wire, seems to have a positive effect on the sound.
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Old 3rd May 2005, 10:58 AM   #4
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Hi Mark,

I completely agree with RITCHIE about the drastic effects of seperate fuses and I dont think it will do any sort of improvement in sonic quality.

regards,
Kanwar
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Old 3rd May 2005, 11:06 AM   #5
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Fuses are not good... To even attempt to protect the semis, they have to run at very close to their overload limit. This leads to heating with current demands, and as the fuse gets hot, it's resistance increases, lowering current flow...

If you have to fuse anything, just fuse the outputs. Run the rest direct from the PSU. Local decoupling for each stage, (Thanks Pavel), is a good idea as well.
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Old 3rd May 2005, 11:10 AM   #6
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Quote:
Originally posted by pinkmouse
..........
If you have to fuse anything, just fuse the outputs. Run the rest direct from the PSU.............
doesn't that increase the risk of fire?
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Old 3rd May 2005, 11:20 AM   #7
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Fires in electronic kit usually are caused by long term overheating of components, and a fuse won't protect you from this. Most other failure modes are explosive, and are not sustained enough to cause the heating that ignites other flamables. If the psu inputs are properly fused, and all connections are tight, then an amp is as safe as you can make it, (providing of course it's not filled with paper, thin bits of wood, or a large quantity of dust).
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Old 3rd May 2005, 11:26 AM   #8
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At risk of contradicting pinkmouse I will say just leave the amp alone Fuses should not be run close to their limits for the reason mentioned by pinkmouse, however, a fault usually results in a short of some kind so the fuse will blow OK anyway. The ripple caused by a power amp will far exceed any current ripple caused by a fuse impedance.
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Old 3rd May 2005, 11:37 AM   #9
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Quote:
Originally posted by richie00boy
........... The ripple caused by a power amp will far exceed any current ripple caused by a fuse impedance.
Yes, but the current flow and hence volt drop across the fuse is also modulated by the music. Which although lower in magnitude than the psu ripple, will be of a higher order.
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Old 3rd May 2005, 11:46 AM   #10
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By PSU ripple I meant the modulating of the PSU by the music demands, not the intrinsic repetitive/consistent charging ripple voltage, thus I believe that my original statement still stands.
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