Home made speaker protection anyone??

thumper69

I'm not thinking about woofers.
Not that Im too cheap to buy commercially available fusing links, but I made a few of these for the fun and tested them on a pair of junky Aiwa speakers and they actually work pretty good. I wonder if I should use slow blow or 12v bulbs just so I could have a little "warning glow" before they pop when they are in real duty. I doubt I will ever get that loud again in20181025_102716.jpg 20181025_102351.jpg 20181025_102918.jpg 20181025_085254.jpg real life though so these should be fine. What are anyone's thoughts on my project here? Where did I go wrong and besides cleaning them up and shrink tubing the bare wires to make them pretty ish and safe from shorting?
 
i use fuses on my main speakers. But they are hard to choose the right one because Ohm's law gets tricky here. Since the signal through the fuse is AC not DC. For up to a 35w per channel drive, I think I used 1A Slo-Blo. Whatever you pick, buy a few different values and experiment, so long as you are using a Solid State amp. Use a small one first and turn it up to loud level, if it blows before you think its too loud, try the next size up. Do not do this with a tube amp, they can't take being driven without a load. Its really only to prevent a catastrophic failure, like your speakers catching on fire.
Don't laugh, it happened to a friends band once. An amp let go with DC out and the woofer caught on fire !! Then someone said, " Excellent light show dude!"

I double-checked and i do use a 1A Slo-Blo. for amps. up to 35 w. Tube.
 
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That's some great information right there. Its a shame I dont understand 90% of it lol. As far as nuisance blows, none so far but like I said, 85% of our listening is done at fairly low volumes. That way I can keep the amps turned up for maximum dynamics but if I really want to put the coal to it I lower the amp outputs to about noon or 1 o clock and that way as the volume increases my fuses and therefore my speakers stay whole and I don't lose anything otherwise as far as my tin ears can tell. If it bears out after a while fatigue sets in and they blow frequently, they only cost a buck for 6 and it only takes me 15 minutes to make up 3 sets. So far so good.
 
From the Heathkit AR-1500 assembly manual:

View attachment 1314811 View attachment 1314812
Ribbed, for everyone's pleasure lol. Thanks satellite, that cant be more clear and consice. Those do look a lot like the fuse blocks on the back of Bozak Listener Series speakers I have except only the blades show, the plate must be mounted inside the rear baffle. I am going to go from the 1 amp fast blow to a 2 amp fast blow and compare them on the sacrificial speakers.
 
Although, now that I have gotten down there and read the information placard affixed to the rear panel of my 1976 OLAs, they recommend a 1 amp slow blow for protection. It also says that it WILL NOT protect the speaker from sudden transients (needle drops). I have 1 amp fast blows just for that reason, they go first. If I double the fuse to a 2 amp fast blow, will that be enough to protect my speakers since the manufacturer reccomends a fuse half the size? Or will the 2 amp fast blow let enough power through to damage my speakers before it goes? In all honesty, this is mostly theoretical as I can never imagine turning up the volume more than 11 o clock on the dial where it is almost beautifully painful to listen to already. At my mostly conservative volume levels, the sound is just fantastic and powerful and you can just feel that there is a monster hiding in there somewhere. I am extremely pleased by the bridged mono dual amp setup can't you tell?
 
smaller fuses are safer, of course. Upsize it only if you blow them very often while listening.

I've installed Polyswitches (auto resettable fuses) at my test speakers, they saved them a couple of times.

If you plan to use polyswitches in the future, keep in mind that the "rating" you see in the polyswitch body is the Ampere at it won't trip. The tripping current is almost twice that value.
 
smaller fuses are safer, of course. Upsize it only if you blow them very often while listening.

I've installed Polyswitches (auto resettable fuses) at my test speakers, they saved them a couple of times.

If you plan to use polyswitches in the future, keep in mind that the "rating" you see in the polyswitch body is the Ampere at it won't trip. The tripping current is almost twice that value.
That makes good sense as well. Well, if it ain't broke don't fix it is where I'm at. Everything's working perfectly and sounding better than it ever has before. I think I'm going to leave well enough alone and just play around with the cosmetics. Maybe get a few of the inline fuse holders just so I can easy swap them out for a 2 amp if we ever need to blow a wall out or just swap the 1 amps if they start to fail with fatigue.
 
Ribbed zip cord usually identifies the neutral/negative conductor,,, not sure it carries over to speaker cables,,, but it is there for identification...
 
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Ribbed zip cord usually identifies the neutral/plus conductor,,, not sure it carries over to speaker cables,,, but it is there for identification...
Yes sir, the ribbed wire in zip cord/lamp cord always indicates neutral in 120 VAC applications, but in this case is merely used
to identify the plus (or non-ground). Of course the electrons don't care about the color or texture of the wire insulation.

They sure liked to use the lamp cord as speaker wire back in the day. I'm guessing it's because that's what was readily available. (?)

Also, for what it's worth, the old Heathkit manual specifically says not to use "slow blow" fuses.
 
Yes. I pulled the "ribbed" comment from the Heathkit diagram posted above. I myself am not using that type. Advent reccomends the slow blow fuses I mentioned as that is the speakers I am using. The Heathkit graphic so graciously provided was to demonstrate the fuse block more so than the wires going to it. So far, after 4 days of 12 hour straight use each day, nothing but sweetness. I can't imagine that would change as the volume stays pretty low all the time except for every now and then one of us bumps it up for a particular track we like. I wanted the headroom 2 seperate mono amps would give me so at the lower volumes specifically the dynamics and punch are still there, but the fuses are there just in case. It has worked better than my expectations and even the wife (who has better ears BTW) is smitten with the new sound coming out of our old speakers.
 
Here what I've done so far. I used good old removable dielectric epoxy to hold the fuse block to the backs of the speakers so they can be returned to as new in just a few minutes if wanted.20181029_111253.jpg
 
A/R recommended fast acting fuses and the values were surprisingly low. 1.25 amps for the AR-3A. They claimed it would handle 67 watts for 10 seconds, 22 watts for 30 seconds, and 10 watts long term. Remember that these are 4 ohm speakers so the current would be double. Saved me during a test. I was working on an electronic crossover and had neglected to include the resistors from input to ground. This would allow an open input to float to the supply voltage and a very high spike when connected to the power amp. Very loud, but quick, POP. Went through several fuses before I solved that one but the speakers survived.

Another solution is covered in Doug Selfs power amplifier books. This is a circuit that connects between the amplifier and the speaker that can include turn on delay, immediate disconnect at turn off, and disconnect if DC is present. It can also include input for a thermal shutdown. 7 transistors, 14 diodes, 17 resistors, 5 capacitors, one relay. Covers both channels.
 
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