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Fuse blown on RB-1080 with new pair of DynAudio's

Hi all,

I purchase used RC-1090 and RB-1080 here last week. I've been using them with a pair of old speakers that I have. They work fine so far.
This weekend, I bought a brand new pair of DynAudio Audience 82 + Audioquest Dimondback XLR balanced interconnection + cheap 18 gauge speaker wire from RadioShack (temporary until I get better speaker cables). I hooked them up and listened for about 3 hours. Then I read somewhere that the speaker wires should be the same length, so I shut them down and trim 1 of the longer speaker wire to have the same length as the other. When I hook them up again, I got no sound to both of the speakers. I also noticed that when I hook the wire to 1 of the speakers, I heard some popping sound from the speaker. I went through all the steps that I know of to try troubleshooting the problem. Finally I pinpointed it down to the amp (RB-1080). The internal fuses were blown. Through out dozen of time trying connect/disconnect the speaker wires, I don't think I ever let the +/- part of the wires touched.
I bought some replacement fuses. But the fuses just kept blowing. At one time I was able to listen continuously for a few hours. But as soon as I turn the amp off or turning it on, the fuses blown again. I already made 2 trips to RadioShack and blow 16 of them fuses. Finally, my amp blows the fuse on the back of the amp. So as this point, I'm not sure what I should do.
So here are my questions:

1. Is there something bad with my new DynAudio speakers? How can I tell whether they are still in "perfect" condition (as they are brand new)? Have I done any damage to them? Is there a way of testing and now for sure?
2. Is there a minimum length of speaker wire required? Are the cheap 18 gauge speaker wires the culprit?
3. What should I do next?

Thanks in advance for any suggestion.
truongphunhuan
8 responses Add your response
duane
189 posts
 
This would be the advantage of buying from a real dealer.

You most likely did not damage the speakers and you can use an ohm meter to verifiy that there is not a short. (Unless the voice coil is shorted in a certain postion during cone travel on the driver).

If it is popping fuses like you described there is a short in the amp. Verify this by replacing fuses and try powering it with nothing hooked to it. If it blows then the amp needs repaired.
cerrot's avatar
cerrot
1,700 posts
 
Any chance that when you spliced the speaker cables, you shorted them out? The rat shack cable is cheap enough - try making another run of cable.
xti16
1,525 posts
 
Maybe see if you can find a higher quality fuse than the rat shack type. There have been a couple of threads regarding the quality of those fuses. Stick with the same amperage and voltage rating though until you can determine if its just an amp problem or not. Putting in a higher amp rated fuse may possibly cause more damage than you already have.
duane
189 posts
 
I forgot to say that you need to make sure you are using slow blow fuses. Rat Shack seldom has fuses for Rotel becuase they are unusual.
truongphunhuan OP
1 posts
 
Thank you all for responding. I really appreciate your help.

I stopped by Rat Shack today after work to get some new fuses. I brought along the blown AC fuse from my amp. What printed on the fuse was BUSS AGC 12 on one end, and 32V on the other end. The gentleman who works there helped me find the fuse. We looked up online and found the spec of the fuse. It's 32V and 12A., but we couldn't find any fuse that's 32V. Now that I just saw the message from PENG mentioned about 3AG125V12A (I assume it's 125V and 12A), I realize the previous owner had the 32 V fuse in it all a long.

What would be the effect of a lower voltage fuse (32V vs. 125V) on the equipment? Would that be the root cause? And why did many rail-fuses get blown first before the AC fuse was blown?
magfan
1,583 posts
 
Fuse voltage doesn't really matter.....
DON'T use slow blow unless it is the stock fuse required.
AGC fuses are NOT slow blow....what is? MDX?

Is there any burned electronic smell coming from the amp?

18ga wire? a little flimsy unless the run is very short, and than.....If you want a beefier, cheapo test wire, get a 12 or 14 ga extension cord and do a snip snip.....

Did you short anything out when doing the 2nd set of connects?

How loud did you crank it? Did the DynAudios show any....distress?

Aren't you glad you're not going thru 30$ per HIFI tuning fuses?
dan_ed
2,451 posts
 
The fuse is fine. Fix the short in your cable and you should be back in business.

I have learned that in the DIY world, ALWAYS suspect what you did yourself first.
keneallyfan
26 posts
 
If you had the amp powered off as you say, I don't think you should have heard any sound coming out of the speakers while connecting the wires. I suppose it's possible that a discharge of static electricity could cause a popping sound, but I don't think I have ever experienced that in close to thirty years of owning stereo equipment. Are you sure you had everything off when you changed the speaker wires?

A very good practice to get into is to turn off and unplug all the equipment in your stereo before you change any wiring.

In any case, a fuse is a protection device. It is designed to fail when there is excessive current flow to protect more expensive parts inside the circuit. They do weaken over time, or may sometimes pop due to a current surge or something.

You change the fuse once, and if it pops again, then there is something else that is causing the fuse to pop. You never, ever trying changing the fuse a dozen times.
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