Excessive speaker impedence cause explosion?

[IIIBaroqueIII]

***See Photos Below***

I've got a Pioneer SX-303R Stereo Receiver, about 10 years old. It only says it can handle 8-16 ohm loads but I have a pretty nice pair of 3 way speakers I assembled which are 24 ohms, (three 8 ohm speakers per cabinet). This was running great for about 6 months untill the other day I was listening at normal volume when the left channel just stopped playing, seconds later followed by a huge blue spark/explosion located towards the left, back corner inside the receiver...a late 4th of July present.

I ripped it appart and from what I can tell from the smoke and ash crap, the part that looks like exploded looks like the bigger transformer but smaller and in the middle has copper windings facing up. I'm guessing this is the output transformer exploded due to overheating because of too much speaker impedence. Someone please inform me on what too much resistance can do (or did do haha) and what parts I damaged.

THANKS!
Dave

 

[markw]

You hooked the three speakers in series?

That's the only way you would wind up wit ha 24 ohm load, and even that would be frequency dependent.

Most people use a crossover which would result in a more "normal" impedance.

In any case, I doubt it was the speakers that were the cause of the problem.

FWIW, that looks like a power transformer to me. I didn't notice any output transformers, which is normal on solid state equipment.

 

[IIIBaroqueIII]

Yes, their in-series.

 

[j_garcia]

With NO x-over?

 

[mulester7]

Yes, their in-series.

.....it sounds like your amp section was on it's last legs, IIIBaroqueIII, but I'm dying to know your wiring configuration concerning the speaker....please, start at the inside of the + post on the back of the speaker.....a wire went from the positive post inside to which element and which terminal on the first element?, and take it on through the whole loop or loops, please.....

 

[PENG]

If they are in series, it should not cause your amp to explode. At a given voltage, more impedance means less current. It could be due to insulation failure, resulting in a short in the transformer winding. Whatever the reason was, it was not due to the high impedance.

 

[j_garcia]

Higher impedance does mean less current is drawn, but if you have to turn it up to 100% amp gain to achieve a given volume, of course it is going to fail at some point, especially if it is older. However, I have to agree, it would still be much less likely to happen in a situation like this.

I'm curious how you have them wired as well.

 

[annunaki]

I could see that happening with a low impedance load, but a high impedance load throws up some questions. If truly wired in series it would be a 24 ohm load. However, if in parallel it would present an 2.67 ohm nominal load. This could cause problems.

 

[mulester7]

.....Gentlemen, the bottom line here might be,.....to straight-wire elements in a speaker enclosure brings ear-splitting raspy at best....you MUST have ceiling or floor rolloff concerning signal-sent to ALL speaker elements....

.....a three-way 8 ohm crossover from Radio Shack runs about 10 bucks....you take the + and - wires to the internally-mounted crossover....then run a + and - wire from each section of the crossover to the appropriate speaker element.....Radio Shack has 8 ohm two-ways also....varieties of 4 ohm crossovers also....

.....this stuff ain't that difficult, but you have to step into the water.....

.....edit....sure, there are better crossovers to be had than what Radio Shack sells, but they actually do a decent job for about a ten-spot......

 

[PENG]

Higher impedance does mean less current is drawn, but if you have to turn it up to 100% amp gain to achieve a given volume, of course it is going to fail at some point, especially if it is older.

I was thinking about that possibility too.