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B & O S-75 Crossover Rebuild

Z

zbadboy69

New Member
I just purchased a pair of B & O S75 speakers that had the common three alarm speaker box fire:smoke: Prior to posting this, I PM'd Zonker92 for information about these speakers. He was kind enough to provide me with a lot of links about rebuilding these speakers. Thanks Zonker.

In the process of rebuilding these I have removed the worst of the two boards to get some info off the caps and resistors. Unfortunately a few are damaged to much to get info off of them. Reading other posts provided me with this information for the resistors.

The resistors (little dark sticks) are supposed to be:

1 ohm x 2
2.2 ohm
3.3 ohm
4.7 ohm x 3
8.2 ohm

The numbers I have are listed below. They all had 204-9 stamped on them which I am assuming is a manufactures number. The following is what I was able to obtain from 6 of the 8 resistors.

3W 4R7 10% quantity 2

3W 2R2 10%

3W 8R2 10%

3W 1R0 10%

3W 2R7 10%

One was burnt and held together with electrical tape. I was unable to get the information off that one. Another one looked exactly like the other ones but did not have writing on it that i could read.

How do these numbers match up with the numbers provided in the post I have read? Would it help if I provided the caps the resistors are connected to for the ones I have no info on?

I tried to attach a photo but it didn't work.
 
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There were also seven caps. The bulky white one was fried real bad. The info on the white one came from another post.

White one is listed as 2.2 10% 250 MMK evox

47MFD 40V

33MFD 40V

10/40V

3.3 40V

47 MFD 40V

The last one is the one that is on the far right side of the board. The writing is faced down so all I could read from it was 12uf.

Any help in identifying what I need here is much appreciated. I understand this thread needs pics and I plan to get them posted and document this rebuild for other AKers.

Thanks
 
I looked at the resistors again and here is what I have.

3 3W 4R7 10% = 4.7 ohm x 3

1 3W 1R0 10% = 1 ohm

1 3W 8R2 10% = 8.2 ohm

1 3W 2R2 10% = 2.2 ohm

1 Fried in half = either a 1 ohm or a 3.3 ohm

1 Unable to read = either a 1 ohm or a 3.3 ohm

This is how I decode these I just don't know the other two.

Thanks
 
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The white box in this pic is the one that burned up on the board. In this picture, the spot where the white wire is crossing the resistor is where it was burned in half on my crossover. Does anyone know what Cap would be the correct replacement? Thanks
 

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Here are pics of the speakers. They sure look nice. However, they sounded like they had a blanket over them. So I researched on here and found out about the infamous crossover burnouts on B&O S75's. That is what prompted me to open mine up.
 

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zbadboy69 said:
There were also seven caps. The bulky white one was fried real bad. The info on the white one came from another post.

White one is listed as 2.2 10% 250 MMK evox

47MFD 40V

33MFD 40V

10/40V

3.3 40V

47 MFD 40V

The last one is the one that is on the far right side of the board. The writing is faced down so all I could read from it was 12uf.

Any help in identifying what I need here is much appreciated. I understand this thread needs pics and I plan to get them posted and document this rebuild for other AKers.

Thanks
Click to expand...

OK well basically for caps you know everything you need to know.

You are looking for non-polar caps. Film caps are always non-polar but values bigger than 20uf can be tricky to find.

The voltage rating from the factory probably should have been 100v rather than the 40v they are using. So replace with parts rated for at least 100v.

the 2.2 is 2.2uf, it's a film cap. unless it looks damaged it's probably fine.

the numbers on the others are all in microfarads - 3.3uf, 10uf, 12uf, 33uf, 47uf.

My general recommendation is to visit www.madisoundspeakerstore.com and look at the caps and resistors they have available.

For the resistors, get the same resistance value but get 5w or larger power rating since 3w was clearly insufficient.
 
When I opened them up this is what I found inside the worst of the two. The other one is burnt but not as bad as this one. In the picture you can see how it burnt the cross brace and the enclosure for the mid. The enclosure only got deformed a bit but did not burn through.
 

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And if i were doing it, I would absolutely use film caps for the 3.3uf, 10uf, and 12uf positions.

a 3.3uf cap is not expensive. Madisound has a 'surplus' 10uf polypropylene for 60 cents which is excellent. They also have a TRW 2.0uf cap (under 'surplus caps') for 35 cents which, paralleled with the 10uf, makes 12uf.

It would be possible to parallel multiple 10uf caps + other caps for the 33uf and 47uf positions but sometimes you end up with three 10uf caps that aren't quite 10uf and need more than 3uf to complete the network, and to know that you need a capacitance meter. So for those, you could get bennic electrolytics which will work just fine - just replace them again in 10 years or so.

OR, Apex Jr. sells (somewhat large) Aerovox 20, 24, and 28uf film caps for just a few bucks each. Two of the 24uf for the 47uf position, a 24 and a 10 for the 33uf position. these will be Close Enough.
 
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You said "And if i were doing it, I would absolutely use film caps for the 3.3uf, 10uf, and 12uf positions." Would you mind explaining the importance of Film caps here? Thanks
 
Film caps sound better (many believe) and last longer (all agree), than electrolytics.

Cap and resistor shopping (and electronics component shopping in general) is an art, but it gets easier with time. You usually work your way down from categories (e.g., 5-watt resistors, or a given brand of resistor or cap), narrowing the selection until you arrive at the item you want. On Parts Express I usually pick a brand of cap then start sorting by capacitance. Or you can search by capacitance. With resistors I usually look at the Mills brand and then pick the power rating, then the value.

Happy to help!
 
I've got these speakers. Once you get them up and running you shouldn't be disappointed. Mine need to be recapped (they're not burnt, just old) but I still think they sound amazing. I hope it all goes well!
 
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