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C75 & CX100 project

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Michael
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Michael Posted: Mon, Apr 20 2015 4:17 PM

Hello,

Recently I bought a pair of C75 and a pair of CX100´s as some of you might already know. 

I have ordered new foam surrounds and I look forward to take on that project.

However I have also noticed that the speaker cloth is not the same on C75 & CX100 and the cloth on the CX100 in particular has been fading because of sun or smoke. I also noticed that the stripe on the side of the speakers are yellowish on the CX100 while they are completely transparent (just glossy) on the C75´s as they should be.

I wonder:
• Can I fix the yellow stripes? Can they be removed, cleaned or replaced?
• Can I get a good replacement fabric anywhere and make a perfect replacement? They must look as good as new with the same kind of texture and feel. I want the real C/CX-experience.
• Can the C75´s be wall mounted in any way? I don't think so. Just curious.
• I need suggestions on nice looking cables for them also. 

A fun fact is that the logo is different on the two pairs. The C75 has a "full" & sign whereas the CX100 has the newer & that lacks a part of the line. Probably a quite new pair. 

I don't have a clue what to use the speakers for so suggestions on that are also welcome. Otherwise I am just happy to have the project to fix them as I enjoy that. Then perhaps they will get new homes, or stay in my apartment or perhaps in my office at work. Who knows. 

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Søren Mexico
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I made mine with new surrounds, using the fabric from Parts Express, not really black, there is some deep brown in it, depending of how the light falls on it, I later found a better one on Amazon, Uneeksupply.

Upper one Parts Express lower Amazon my thread here make sure you get thin cloth that stretch in both directions, the space between the the plastic fret base and the speaker front is very limited. I polished mine with a car polish/cleaner and then gave them a layer of car wax, The stripes has a very faint yellow shine, but only in some light conditions.

These speakers are very placement sensitive, ear height and close to wall in my opinion the best, a month ago I had them set up in a 4 car garage for a party, connected to my BM 5000 and BG 5000 pizzabox, I was impressed of the sound, they played for 8 hours continuously with volume on high to very high, no problems what so ever.

Wall mount is possible, there is a hole in the back where a small hook goes in, but best is a small board

Collecting Vintage B&O is not a hobby, its a lifestyle.

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Mogelmose replied on Tue, Apr 21 2015 8:37 AM

Michael:

I don't have a clue what to use the speakers for so suggestions on that are also welcome. Otherwise I am just happy to have the project to fix them as I enjoy that. Then perhaps they will get new homes, or stay in my apartment or perhaps in my office at work. Who knows. 

CX100 is great for bathrooms and kitchens. They can withstand the humidity and the sound profile, not to much bass and a clear top makes the sound okay with the acoustics in the bathroom.

Pair them with a MCL2A if you have MCL or Beolink Passive if you have Masterlink.

Right now i have CX100 in my livingroom. CX50 in my office and i think am going to collect CX's for the Bathroom and the Kitchen too. I like them over the Beolab 3500.

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Michael replied on Tue, Apr 21 2015 9:57 AM

Hi Søren, 

Thanks for your suggestions and picture. I think both fabrics looks a bit bright but it is probably just the picture. The lower one looks better but the texture seems better on the top one. I think I will have to look carefully into that if I am replacing the fabric at all. Perhaps it can be cleaned?

The yellow stripes is probably a result of UV damage. Guess it will be hard to fix but I think they would look better without the stripes all together then. If they can be removed.

I think someone used sand paper on a pair of CX100 and while it did make them look really nice it also is not something I want to do since aluminium isn't the best thing to breathe or get into your body.

Not sure about car wax either, I want them as clean and natural as possible.

I am curious about the sound and a bit sad to hear that they are very placement sensitive. Perhaps ear height is possible to achieve but they look very nice on the floor too. The C75´s don't have a hole in them as the CX100 so I don't think they are possible to mount on a wall though.

Looking forward to getting the project started :-). 

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Michael replied on Tue, Apr 21 2015 5:58 PM

Just realized that perhaps I should look over the filters inside the speakers and replace the old caps? I have not seen the filters of either C75 or CX100´s yet so I am not sure if there is anything to do. 

I also think about adding rubber feet to them and looking for nice speaker wires. Suggestions? 

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There is one cap inside on the crossover on thecx100. Mine actually blew once. Havent come around to fix it yet.

"You think we can slap some oak on this thing?"

leosgonewild
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There is one cap inside on the crossover on thecx100. Mine actually blew once. Havent come around to fix it yet.

"You think we can slap some oak on this thing?"

Michael
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Michael replied on Sun, Apr 26 2015 9:55 PM

I began taking the speakers out today.

Noticed that C75 has black plastic on the fabric-frame and the CX100 has white ones. I am thinking about washing them somehow (Don't want to remove the fabric from the frames).

I was surprised of how short the cables was and that they were soldered. Very hard to move the speakers around without damaging the cabinet because of the huge magnets and the short cables. I accidentally melted a corner of one of the foam rings that lies between the speaker and the cabinet but I think it is fine. 

I removed the back from the C75´s to see the insides and noticed a cap (6,8uF/63V) Elko rauh, W-GERM. I think it is the first time I´ve ever seen anything stamped with West germany.

The C75 speakers had foam rot but had not deteriorated as the CX100 had. The foam surrounds on the CX100 had cracked very badly and was not stiff but gooey. Like a very fat paste. Very, very, very hard to remove and it stuck everywhere. Still have a lot of cleaning to do. I´ll continue when I have more time. It took me several hours today just to come this far. I am not rushing and it´s fun so I just let it take its time, but I wonder if the speakers usually deteriorate like this because it´s a real mess to clean up. I hope the C75´s will be easier..

Here´s a picture from earlier today:

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tournedos replied on Mon, Apr 27 2015 7:10 AM

Michael:


Noticed that C75 has black plastic on the fabric-frame and the CX100 has white ones. I am thinking about washing them somehow (Don't want to remove the fabric from the frames).

Hand warm water and a toothbrush. The frames will be brittle.

And yes the glue-like surrounds are quite the norm with these.

--mika

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Michael replied on Mon, Apr 27 2015 7:20 AM
Ah, thanks for the advise. Regarding the rubbery foams. Any idea of how to remove it properly? I've been using a thin knife and my fingers but there is still a lot of "goo" left.

Also find it hard to clean up the frame. Such a big project :-).

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BO replied on Wed, Apr 29 2015 6:52 AM
Keep track of the speaker drivers positions and part numbers. They're not all the same if I remember correctly

//Bo.
A long list...

Michael
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Michael replied on Wed, Apr 29 2015 8:48 AM

BO:
Keep track of the speaker drivers positions and part numbers. They're not all the same if I remember correctly

Yes, you are absolutely correct!

I noted the following, might come in handy for someone else perhaps?

CX100:
Top speaker: 8480174, 9T71A. Cabling: black-white-, red-red+.  
Bottom speaker: 8480173, 9T71A. Cabling: yellow-white-, orange-red+.  

C75: 
Top speaker: 8480141, Japan, 531TNG. Cabling: black-white-, red-red+.
Bottom speaker: Cabling: yellow-white-, orange-red+. I will note the speaker info when I get home, forgot to take a photo of the note after I noted what it said on the last speaker :-).

(- towards BANG&OLUFSEN, + towards BEOVOX) 

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Stonk replied on Wed, Apr 29 2015 1:34 PM

Yes the C75's are far better made than the CX's which were probably much cheaper to manufacture. The sound difference is negligible thoughUnsure

If you think nobody cares, try missing a couple of payments.

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Michael replied on Fri, May 15 2015 8:56 PM

I have been cleaning them a little a few times over now and I don't think the cones can be cleaned much more. However, the metal frames can be cleaned up a lot more.

Today I tried to remove the thick black glue and the remaining foam. Since it was glued very hard I used a knife to cut it away. I managed to do so quite good.

There is still a lot of adhesive left and it is not very easy to remove. I have tried petrol, acetone and acetone with oil. I was going to buy nail polish but the store had no bottles left. I think I can glue the new surrounds on now but I feel like it would be best to clean it up perfectly first. 

Any ideas? Perhaps I should try steel wool? 

I also noticed that the main difference between the top and bottom speakers are that one of them has a solid magnet and the other one has a hole in the middle. I suppose this makes them play a bit differently. It is the same both on C75 and CX100. The C75 speakers appear much more well built than the CX100 speakers. 

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Dillen replied on Sat, May 16 2015 6:55 AM

NO STEEL WOOL !!!!!

No matter how careful you work, stray strand fragments WILL end up inside the voicecoil around the magnet centerpiece and
you can throw the drivers away.

Martin

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Michael replied on Sat, May 16 2015 12:14 PM
I'm not sure I understand. Why would metal fragments go into the speaker? I'm not going to do the shimming procedure on them so I don't think it would be an issue.

But any other ideas how to get the last adhesive and glue off the frames?

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Dillen replied on Sun, May 17 2015 6:13 AM

Steel wool is iron strands. It can't resist magnets and it will find a way in, trust me.
Some drivers have ventilated magnets, to name one way - but having it sit around the spider does not
improve sound quality either and it's not particularly easy to remove from there.

IPA, patience and a surgeons knife.

Martin

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Michael replied on Sun, May 17 2015 11:42 AM

Dillen:

Steel wool is iron strands. It can't resist magnets and it will find a way in, trust me.
Some drivers have ventilated magnets, to name one way - but having it sit around the spider does not
improve sound quality either and it's not particularly easy to remove from there.

IPA, patience and a surgeons knife.

Martin



Im not so sure IPA is good for the speakers (or for my handiwork either BeerBig Smile)

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Ben_S replied on Sun, May 17 2015 11:49 AM

As Martin has many years of experience dealing with vintage B&O I would listen to his advice!

Ben

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Dave Farr replied on Sun, May 17 2015 11:51 AM

I used IPA on my CX100's and it worked a treat and made the job really easy.  Take heed about the steel wool too.

Dave.

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Michael replied on Sun, May 17 2015 11:58 AM

For me IPA means this: http://en.wikipedia.org/wiki/India_pale_ale. Im starting to realize you mean something else, but what? Wink

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tournedos replied on Sun, May 17 2015 12:14 PM

Michael:

For me IPA means this: http://en.wikipedia.org/wiki/India_pale_ale. Im starting to realize you mean something else, but what? Wink

That may help if you drink it yourself Big Smile but in this context IPA = isopropylalcohol.

--mika

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Michael replied on Sun, May 17 2015 12:24 PM

tournedos:
That may help if you drink it yourself Big Smile but in this context IPA = isopropylalcohol.


Haha, well now it makes sense! I do have plenty of isopropylalcohol at home. I didn't think it would work well on it but I will try today!

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Michael replied on Sun, May 17 2015 9:59 PM
Finished the reforming of all eight speakers today.

Took quite a while and I was very careful.

I noticed that I could easily see how the new rings was sitting through the holes in the metal frame. I used my vision and adjusted them to look as centered as possible. I then waited until the glue dried and mounted the rings to the metal frame too.

Using cotton buds I pressed down on the foam a few times the following hours to clear air bubbles and to keep the foam flush against the frames. Seems to have worked out well. Will let them dry over night and possibly assemble the speakers tomorrow.

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Michael replied on Mon, May 18 2015 3:30 PM


Probably looks like I used a lot of glue - which I did, although much less than was recommended by the seller. I could clean it up but I prefer to have the glue around to keep it in place and keep it airtight. I also let it rest in the speaker cones also, for the same reason. I don't think it will affect performance negatively. And I can always cut the excess away with a sharp knife If necessary. I used the glue from audio friends and it seems to be of high quality.

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Michael replied on Tue, May 19 2015 11:21 AM

Project finished! I assembled everything last night.

Took quite a while because of the short cables and having to solder everything. Quite difficult assembly I think, the speaker magnets are so strong that they are difficult to move without the speaker pulling towards the case (the magnets being almost the entire weight and the speakers almost no weight). And the screws for the C75´s are horrible compared to the CX100 screws. They are very long philips screws that cam out _a lot_ and they are very fragile. No matter how careful I was I still damaged the screw heads a bit, I used duct tape to clean the screws from metal dust that was the result of the screws bad quality.

The CX100 screws however was Torx T10 and very short. Much, much better - probably the only improvement over the C75 design. 


I found it interesting that the color of the metal frames of all the speakers are military green. Makes me wonder if they are fitted inside the Lamborghini LM002 or any other military things Smile. Another interesting fact is that the CX100 speakers shares the same internal volume, meaning one speaker pulls the other and vice versa. I wonder how this works out in reality, since both speakers are connected correctly with positive and negative connected to the respective same. For me it seems the other speaker would "brake" the other one = effectively cancelling sound. But perhaps this just means tighter sound. I am not sure. 

C75 has bass ports on the back and separate volumes per speaker so that they don't interfere with each other. Both C75 and CX100 shares the same element design: upper woofer, tweeter in the middle and lower woofer with midrange support. I am curious to hear how different they might sound since the biggest difference is the cabinets. I suppose the mid-range might sound better in CX100 if they are placed low since the speakers are placed at an angle in those speakers and not in C75. 

C75 is considerably heavier than CX100 and today I bring one with me to work. I commute by train and one is heavy enough, next one tomorrow! 

As I am very curious to hear the result I will try one speaker today Smile. I have a BeoSystem 5500 at work, that I recently purchased too. Should be a nice looking/sounding system I think.









Of course the speakers should be carried in style :-).

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Don't you have two hands, Michael  Big Smile

Looking forward to read about, what your 'colleagues' at work say, when they hear these little beauties.

Enjoy Smile

MM

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Michael replied on Tue, May 19 2015 12:58 PM

Millemissen:

Don't you have two hands, Michael  Big Smile

Looking forward to read about, what your 'colleagues' at work say, when they hear these little beauties.

Enjoy Smile

MM



Haha, well I do have two hands, but if I hold the speaker with two hands, the cabinet moves instead Smile

I also look forward to that =).

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Michael replied on Mon, Jun 8 2015 10:25 PM

So I tried something else today. I remembered a few days ago that I had two BOSE Acoustimass subwoofers in the basement and I took one up to my apartment to try with the CX100´s. And.. it really works well! It sounds like a Beolit 12 but with more power. 

I took a short sample video with my iPhone 6, the sound is actually captured quite good: https://www.youtube.com/watch?v=_HoB37ta3U4 

 

I think I will try this setup at work where I have my C75´s also. And sell the BeoSystem 5500 again. It takes up a lot of space.

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Great video. You've done a great job on the restoration Yes - thumbs upLets have a Party !!!
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