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
Hello everyone,
I purchased a pair of S75's about six months ago and have more than happy with them. Upon further inspection however, I noticed that one of the midrange speakers was not working. Set up with a 5.1 system it was difficult to hear the absence unless you were close to the speaker so it didn't bother me. I recently got a moment to open it up in attempt to locate the culprit. Let's just say it was quite obvious (see photos below). After opening it up, the woofer wire fell apart. It amazes me that any sound came out of any of the 4 speakers. After a few hours of google image searching, on the spectrum of "light toast" to "your toaster melted", I fell as though I landed the latter. I opened the other speaker for comparison and to make sure it wasn't in need of some major TLC as well (pictured below). Thankfully it looks brand new. I will likely order two of all replacement parts and repair both crossovers to the same specifications for continuity.
My question is in regard to the inductors. I was originally going to ask about specifications for the capacitors and resistors but was able to locate a schematic with the values (included below). The schematic does leave some information out about the inductors. As you can see in the photos, I do not think it is a good idea to replace everything and leave the charred inductors in there.
The schematics state that the most heavily charred inductor has a specification of 0.26mH and has a ferrite core. Looking primarily on Parts Express but also some google searches, 0.26mH inductors are difficult to find. 0.25mH and 0.27mH inductors are plentiful. I also noticed that with differences in wire gauge comes differences in Ohms. Is there a way to tell, or does anyone know what gauge wire these inductors have or their original Ohm rating? Would using a 0.25 or 0.27mH inductor make much of a difference?
If the seemingly infamous "Martin (Dillen)" or someone similar stumbles upon this, they are Type 6313.
Any help is greatly appreciated.
Woops, charred one is 0.7mH. The above question still stands though.
Dont rely on the schematics and the component list, mostly the crossovers are different so where possible check the values on the crossover component and get new ones as close as you can get, as for the coils wait for Martin, or send him a mail
Collecting Vintage B&O is not a hobby, its a lifestyle.
Oh dear, what a mess. Looks like one speaker was at a party, while the other stayed home.
Are the coils charred too? Maybe it's just my monitor, but I cannot see where.Isn't it just a matter of cleaning the leads that goes to the coils where they've passed through hot areas ?
Martin
Here is a better image to show the inductor. Strange too that it's the only one that I have found that is purple. Looks like it took quite a bit of heat. Any idea of the specifications on these little buggers?
Doesn't look too bad, if you ask me.The color is fine and it was submerged in lacquer to prevent rattling and copper wire insulation breakup.They are very sturdy components. I wouldn't suspect it.
Correct me if I'm wrong, but an inductor is just a loop of wire. I would check it for continuity. If it checks good, then it's probably OK.
I have seen burned out inductors before, but on power supplies. From EE-101, the voltage across an inductor is the inductance times the rate of change in current. If the current is interrupted, you can get very high voltages which may cause it to fail. Inductors can have pretty big tolerances, sometimes +- 50%. An exact match, such as 0.26 mH may not always necessary. But in audio it may be different, so my opinion should be taken with a grain of salt.
andyjsegal: Here is a better image to show the inductor. Strange too that it's the only one that I have found that is purple. Looks like it took quite a bit of heat. Any idea of the specifications on these little buggers?
Maybe you could compare measure coils between speakers if there is difference? If not, they are probably ok.
blah-blah and photographs as needed
Did you get my email ?
I'm with Martin - a few of my projects had inductors (and resistors) that looked bad, but weren't. They should be fine.
But, if you ever need an odd-valued inductor, these guys will wind you anything.
Well I thought I had posted a reply last week but apparently I never clicked "post".... The replacement caps and resistors came in the mail yesterday. Today I'll be attempting a rebuild of nearly all components of the crossover (keeping the original inductors). With the wiring diagram I posted earlier, pictures of the old crossovers, and with majority of the original pieces still connected after removal, I did anticipate it not being so mind-boggling (+ here, - there, but + and - here, this goes straight to the driver but magically passes through these resistors). I'm sure most of you out there find most of this quite simple but with a background in medicine, it's a foreign language. The new resistors are a bit larger so the layout of the crossover had to be altered slightly. Pcitures of them completed should go up tonight.
Thanks for everyone's help!
Make sure you change the components with the ones you find on the crossover, the drawing and part list are not always the same as the ones on your crossover.
I used the original crossovers for a parts list but a couple of the resistors were not labeled so I used the schematics for their values. While the components may be different as mentioned, is it possible that the wiring of the crossover and diagram are different? The input from the din connector does not seem to correspond between the two.
andyjsegal: Well I thought I had posted a reply last week but apparently I never clicked "post".... The replacement caps and resistors came in the mail yesterday. Today I'll be attempting a rebuild of nearly all components of the crossover (keeping the original inductors). With the wiring diagram I posted earlier, pictures of the old crossovers, and with majority of the original pieces still connected after removal, I did anticipate it not being so mind-boggling (+ here, - there, but + and - here, this goes straight to the driver but magically passes through these resistors). I'm sure most of you out there find most of this quite simple but with a background in medicine, it's a foreign language. The new resistors are a bit larger so the layout of the crossover had to be altered slightly. Pcitures of them completed should go up tonight. Thanks for everyone's help!
Even those of us who are engineers in "real life" find it difficult. I had to split my M70 crossovers into 2 separate boards!
Whenever you tackle a project like this, take lots of photos and take lots of notes. Detailing the project here step-by-step on Beoworld can help keep your project on track, both by making a record for yourself, and allowing the experts to offer advice along the way. Plus, it makes it that much easier for the next guy to tackle the same work.
Check the resistors with an Ohm meter, and stay with the original wiring. and as Rich mentions take pics, post here if you need help. All the experts are following.
On the schematic, the (+in) appears to go through the 2.2 cap first, then the 3.3 resistor. But on my crossover, the (+in) connects first to the resistor, which then connects to the 2.2 cap. Seems backwards and also seems like it could contribute to the resistors overheating, cracking, and burning up.
Seems like most crossovers I can find online have the same order as mine but if there is something I am missing, I would rather correct it now than have another crossover melt down on me in the future.
Are your components the same as in the schematics
And are the connections the same in both crossovers
The only difference in the components is on c1 and c4. Parts list puts them at 50u and 37u respectively. On the crossovers they are 47 and 33. Connections are the same in both crossovers.
The resistor next to the plastic cap is really the only failure point I have found on these. Just making sure that the factory didn't wire them wrong creating a failure point.
Then connect the + wire to C2, C2 to resistor, resistor to neg. and check that everything is according to schematics the difference in capacitance is within the 20% limit so thats OK
Great! Thank you Soren.
And you bought bipolar caps - right ?
Well here it is. Bipolar caps, yes. Hours trying to figure out the wiring of this thing, yes. A mess of wires that is strangely organized, yes. Do all of the components work flawlessly, yes. It is also now wired per the schematics. Only a couple of the caps are film, had to pick them to meet the specs. The speakers sound great. Unfortunately the only thing I have to compare them to is a pair of AR-4x's. Thanks for everyone's help through all of this! hopefully it helps someone else out there.
A few pictures of the process and install, and the schematic I had to draw to make sense of it all.
Excellent work, congratulations. I take it that you glued the caps to the board, right?
So how do they compare to the AR speakers ?
Jacques
The S75's compared to the AR-4x's.
I'm not sure it's the fairest of comparisons given its a 4-way vs 2-way. But with the extra high end and larger low end, they sound much more clear. I rebuilt the crossovers in the AR-4X's and thought that they sounded great, and they do by themselves. But the Beovox's are crushing them right now. I'm sure if I had a pair of AR-3a's it would be a better fight. I have zero experience with top end speakers nor the lingo that accompanies describing sound so with that, I say the highs are high, the lows are decent but could be tighter, and the mid range is, well, mid range. There seems to be a few sounds/instruments that are present with the 75's that are muted with the AR's as well. Brings me back to summer days with my dad blasting Van Morrison while my mom was out of the house. Some day I'm sure i'll upgrade further and be even more amazed.
andyjsegal: On the schematic, the (+in) appears to go through the 2.2 cap first, then the 3.3 resistor. But on my crossover, the (+in) connects first to the resistor, which then connects to the 2.2 cap. Seems backwards and also seems like it could contribute to the resistors overheating, cracking, and burning up.
Sorry, but this doesn't make sense.
It's just a load for the amplifier for higher frequencies. The higher the frequencies, the lower the total impedance of this network (R+C) becomes.
It compensates/corrects the behaviour of the filter for frequencies higher than around the 5-6Khz.
I know this is an old thread but it is such a common problem. Attached is a pic of my burned resistors.
Is there a substitute that will not overheat and catch fire?
Is this the original schematic and parts list or has it been modified?
Also, does it look like the top has blow off this cap?
This speaker was heavily overloaded.There are no modifications or "corrections" that will fix misuse.
Those capacitors are long gone.The resistors may be fine still - check them.Capacitor kits and resistors are in the webshop.
Here is another pick of the same crossover but a different resistor that overheated and melted together two wires. These are all 3w resistors, would 10W help with the overheating? I have worked on a lot of speakers and I have never seen crossovers burn like these. With so many failing in the same manner there has to be a design flaw. I started listing the values off my crossover and they vary from the values listed in this thread. For example, C1 is listed as 50uf and mine is 47uf. R2 is listed as 3.3 and mine is 2.2.
What do the resistor markings 4R7, 2R2, ect. mean?
Here is a better pic of my crossover. It does not appear to have been modified.
I cannot read the designations on the two resistors that have burnt against each other.
This is a very nice pair of speakers with good drivers, nice cabinets and perfect grills. I just cannot bring
myself to part them out.
Check the resistors with an ohmmeter.They don't look too bad in my opinion and could all be fine.The dark marks on two of them are most likely from glue, a little damping material gotten caught there or something emitted from theexploding cap nearby.The melted insulation on two leads is merely an indication that the nearby resistor ran warm - not a problem.
A 10W resistor will not be any cooler than a 3W.The amount of energy dissipated will be the same, but a 10W resistor will not burn through at f.e. 5W, like a 3W would.I would stay with the original specs, because in some cases the resistors double as safety devices ("fuses") for the speaker drivers.
The capacitors will definitely need replacing.