ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Dear,
I've got my crossover burned in a pair of S45-2 's.As you can see the last resistor is totaly burned away.
Does anybody know which resistor it is?I can read the other resistors, but only on the 3.3kOhm it says 3W. What are the other wattages? Or is it alright if i use 3 or 5W for every resistor?
Thanks,
Aymeric
Hello Aymeric,
Dillen (active on this forum) sells recap kits with all the correct caps in it. Also there are many threats about recapping S45's and the different values of the caps.
Déjà vu!
I bought 7W resistors to repair my crossovers.
I find it conspicuous that those resistors should burn so easily, and that they should literally set fire inside the Beovoxes.
Jacques
chartz: Déjà vu! I bought 7W resistors to repair my crossovers. I find it conspicuous that those resistors should burn so easily, and that they should literally set fire inside the Beovoxes.
Deju vu x 2
But in my case it exploded some of the capacitors and wiped out a tweeter as well. Not something I did but I purcahsed the set with this fault and it affected both speakers... and both bass driver magnets had slipped.
It was a bit of work getting them sorted back out but it is absolutely worth it.
I used 5W resistors as replacements.
I've been playing with a set of Beovox S-80.2, and have found that B&O went cheap on some of these parts, and went cheap on some design considerations.
On resistors - going to higher wattage is perfectly fine, and recommended. I'd use 10 watt on most of these myself. The wattage rating has nothing to do with the resistance. It's just the spec. for how much power they can handle. You will have to float them above the board because of size, BUT that is better for heat dissipation in any case.
On capacitors - no reason to use electrolytic s if the values are less than around 20 uf. Better caps, sound better. Lower dc series resistance, and they last longer too. Keep voltage at 50 volts and up.
On the designs - Well, B&O in the S-120.2, S-80.2 and I presume others went to first order type crossovers, and the driver requirements to really do that are extreme. The drivers they used in my S-80.2 almost make it, except for the tweeter. The chosen tweeter(in my units a Vifa 25AG) doesn't have a back cavity, and has both a high resonance and, by today's standards, a high impedance peak, that was completely ignored in the crossover.
The result of this is a sibilant exaggerated high end, most noticeable on some female vocals. To me, it's like fingernails on a chalkboard!
Solutions I'm toying with - Troels has shown a method to modify such tweeters to have a back cavity. I've done this in the past, and it's a pain to do. However, if done successfully this will lower the resonant frequency, perhaps enough that the current crossover topology will work OK.
Another solution, and something they seem to have done in other models is to negate the FS impedance peak electrically. My hesitation there is that even though you take care of the peak, you still will have a rise in harmonic distortion, and that is part of the sibilant issue. None the less, since this is the easiest and least expensive thing to try, I plan on trying that sometime this weekend.
the better solutions - Convert the first order design to at least second order L/R, but....a lot of testing, measuring, optimizing, etc. I don't have the time/patience or the proper tools for that myself. One could also, and this seems like the direction I'll eventually take, would be to replace the tweeter with a unit with similar size(to fit the mid/tweeter assembly), similar output, and impedance at the crossover region, but better suited to a first order crossover. There are a few tweeters that may work well here, but I'm a poor retired, not very healthy senior audiophile with a very limited budget. I'm looking on the used market right now as I think this will be the way I'll end up going.
I'd suggest that anyone not satisfied with the B&O sound consider just updating the tweeters to more modern designs, to avoid some of the issues that plagued domes until the true computer age where finite element analysis, simulation software and even optimizing in a virtual reality have greatly improved the better tweeter designs, perhaps more than any other driver. The chosen B&O woofer in my S-80.2 is it seems to me, a fabulous unit, although here again, baffle step was ignored, among other things. The midrange dome seems to be a good unit, and something about 3"/75mm domes in that range is intrinsically easy to listen to. I have no idea why that is, but in speaker after speaker, the ones I've heard with that size dome always sound real to me. These were the domes with the open, usually felt damped pole piece; not the cheap units with shallow sealed backs.
In summation - these designs can be improved greatly in my opinion, but the basic parts and ideas as used are workable, and of high enough quality to be worth the effort. Especially in today's world, where a good woofer can cost more than the whole speaker back when these were made.
When looked at from that perspective, they are a really excellent value and potentially capable of superior reproduction.
I apologize for taking your resistor question and partially at least changing the topic, but this was the most recent discussion on the general issue of crossovers, so had to take the opportunity to both address your concern, and throw in my additional comments. Hope you don't mind...:)
OLD, Old, oldtableman.