Opinions on adding fuses to power amp

Ah you're talking abput the hatched (scotched) type thing, I`m sure that`s solder paste screen printed on during manufacture of the pcb.

Ron(UK)

precise

solder

None of that on this one but I know what you mean. But some extrusion of solder paste process via a vinyl sign cutter type plotter mechanism in place of the cutter would be more likely than molten solder. Then fused onto the board before populating with components but would that take solder bath soldering of the components afterwards ? The "beefing" is not applied after the main component soldering operation.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

whatever fuse the toroidal gets needs to be antisurge. Toroids are known for their sometimes heavy inrush.

This will give no protection to the output devices of course, it really will be nothing more than basic fire protection.

You'd get much better fuse response if you put them after the reservoirs, because they dont then need to handle high peak cap charging currents.

worst case is 1x not 2x. The common psu rail carries near zero if similar fault currents flow in both + and - rails.

then there would be near zero current in the common rail.

I dont think I've ever seen any attempt to do it to accurate dimensions. Neither flow soldering nor hand soldering work like that.

No, because cu and slobber blow at very different temps. 18A probably wont even be close.

I'm left wondering precisely what youre trying to achieve. If youre trying to protect output devices, none of the above will do it. If youre trying to protect speakers, the above are not whats wanted. If all you want is to prevent charring of pcb due to repeated blowing, its going to be cheaper in the end to prevent the repeat blowing. Really whats propsed so far doesnt seem to solve any real world issue. The amp sounds roughly designed, intended for a limited service life, and to change that you'd need to add a full set of current and safe area protection for the output devices, almost none of which can be achieved with fuses.

What are you really looking to achieve?

NT

I'll repeat it without the clutter.

I'm just trying to fashion a more respectable equivalent of fuses instead of trace burning and rupture.

No, but it's a dumb idea. It's fairly easy to dump solder "accurately" on a trace (if not covered by soldermask, hopefully that's obvious) - just heat and feed solder, it will follow the trace, and you can build it up quite a ways simply from surface tension. If you need more current capacity on the trace, bend up a chunk of copper wire that actually conducts well and solder that on. Solder is a lousy conductor, compared to copper. The copper will hold more solder on there, but most of the current will be carried by the copper.

traces

I get the impression board layout designers just use what has worked before as far as track dimensions etc and don't actually consider in great detail catastrophic failure modes. Yes this kit does support the CE mark. I've not been able to find design data/tables for such traces. I may dig out a low voltage 60 amp transformer fed via a variac and sacrifice some otherwise unaffected tracks on this board to determine what sort of amperage to cause excessive heating and then another bit of track to find the rupture current. Having to avoid localised failure at my test join-points with a lot of distributed solder.

On a well designed circuit board, you can often see which traces are involved with each part of the circuit. Broad traces carry the heavy current, spidery ones are the signal path. I remember a time when some quality gear actually had the signal path screened onto the component side of the board, together with typical voltages etc. That was when they actually wanted us to repair the stuff.

I dont think any designer worries too much about 'catastrophic failure'!

. Yes this kit does support the CE mark.

You still havent shared with us the make and model

Ron(UK)

Just interested ... Do you actually make a living out of repairing this stuff ? If I spent as much time as you seem to, worrying about esoteric things like how much current a track will take before it vapourises, I would long since have ceased to earn enough money to get by on. These days, I find that it has to be 'wheel it in, fix it, wheel it out , invoice it, next please'. If the bit called 'fix it' takes longer than an hour, and the value of the kit is less than 150 quid, that bit changes to 'bin it' ...

Arfa

I don't feel like whipping up bulk supply simulation right now, please run yours and tell me the ripple voltages at 10% conduction and 6.25 % conduction.

Self promotion will get you nowhere in this world.

-- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85.

Michael A. Terrell Central Florida

Phil seems to do well for a week or two then has these psychotic outburst episodes.