Hi, I just purchased B&W Matrix 804 on eBay,, Despite almost 30 years old vintage speaker, it is still in good shape but want to replace the crossover if possible just the capacitor,, There are 2 crossover boards one for lower frequency and the one for higher frequency. The capacitor for lower frequency is Bennic bipola 7mfd at 70 watts,,, Only thing I can find on the web is 6.8 mfd at 100 watts,,,from Bennic. Is there any better alternative? For the high frequency board there are 2 caps from Bennic but they are seems like poly film caps. My understanding is that poly caps usually do not go bad unless it has been abused or do I also need to replace 2 poly caps as well? New to the hifi world and really need your opinion on the subject. Thanks
Indeed, a Bipolar Electrolytic Capacitor is going to be 6.8uF at 70V or 100V in all likelihood. 6.8uF is the nearest common preferred value. Fitting a MKP 250V polypropylene will likely be a bigger component, and is electrically slightly different.
If you can hear the difference from a 7uF, I will be surprised.
Couple of schematics here:
https://www.diyaudio.com/community/threads/b-w-matrix-804.268377/#post-4216882
And the similar P6 which has a simpler bass filter without the shunt 6.8uF capacitor:
https://www.diyaudio.com/community/threads/xover-mods.267472/#post-4181871
B&W Support seems to be down for maintenance ATM, but you can try it later:
http://bwgroupsupport.com/
People sometimes inspect the tweeter for dried-out ferrofluid, which can reduce output, but that needs a delicate touch.
If you can hear the difference from a 7uF, I will be surprised.
Couple of schematics here:
https://www.diyaudio.com/community/threads/b-w-matrix-804.268377/#post-4216882
And the similar P6 which has a simpler bass filter without the shunt 6.8uF capacitor:
https://www.diyaudio.com/community/threads/xover-mods.267472/#post-4181871
B&W Support seems to be down for maintenance ATM, but you can try it later:
http://bwgroupsupport.com/
People sometimes inspect the tweeter for dried-out ferrofluid, which can reduce output, but that needs a delicate touch.
Thank you for advise. I guess I go with 6.8uf for lower frequency,,, that is only thing I can find anyway,,,, what about 2 poly caps in high frequency boar? Do I need to replace them also? Tweeter sounds OK,,, (or at least it is working I should say) ??? I will also look into adding ferrofluid for the tweeter... How difficult the task is?? I find some youtube video and seems like straight forward process.. Thanks
MKP poly types last forever! I'd be more interested in checking the wiring connections are uncorroded by rust.
Check voicecoils aren't rubbing by pressing them in.
Most tweeters come apart easily enough if you suspect dried-up fluid clogging them up.
Be careful to lift the voicecoil off vertically, so you don't break it. Screwdriver job.
Check voicecoils aren't rubbing by pressing them in.
Most tweeters come apart easily enough if you suspect dried-up fluid clogging them up.
Be careful to lift the voicecoil off vertically, so you don't break it. Screwdriver job.
I'd worry about other things, because what you describe is trivial worrying.
Maybe you just don't understand that capacitors and resistors all have what's called a "tolerence level".
Honestly, find some other thing to worry about.
Rather than start a new thread: Can someone with more experience confirm these three caps would be appropriate to substitute for the original ones? My 7 uF, 70 volt cap for the LF was labelled B&W, not Bennic as the OP had on his crossover. It isn't clear to me if this Mundorf would be reasonable substitute or not. (Build type). In addition, I included two photos of how easily one can refresh the ferrofluid. To be upfront, there are many formulations of ferrofluid available, and B&W was not forthcoming in giving me a specification, so I used commonly available 1 inch tweeter packets from online source. Other older B&W speakers of mine, (FCM-8) had seriously caked and muddy and sludgy fluid, and clearly benefited by this type of work. These dated 1997 were not nearly as bad, and I'm not sure it made much difference. Any input appreciated to confirm this is the right path. I recently auditioned some N804 side by side with M804, and it made it very clear that either B&W has dramatically changed the voicing of their speakers, or my M804 have aged poorly in some capacity. I can not rule out completely room acoustics as I listened somewhere else, on his 804's, but this is not a costly or difficult process to swap in fresh caps and maintain the tweeter. TIA.
Your Mundorf replacements are quite appropriate.
Can you give a link to the ferrofluid you used in order to see if it is, in fact, the right type?
Is it possible that the ferrofluid may not have needed changing?
This is a reliable UK source of ferrofluid: https://willys-hifi.com/products/ferrofluid-refill-kit?variant=23293759943
They invite you to contact them about other available formulations.
They invite you to contact them about other available formulations.
I really appreciate that. The notes say they are sourcing it from Ferro Tec in the USA, and thats the name on the label of the packets I have. Not certain the syringe applicator makes a difference. But, to your point, they offer 3 different selections of fluid... not a choice I saw back when I purchased these packets. Thanks!
It says APG L11, 100ul. It has a lot number on it, as well as P/N 340-540 which may be from the supplier Parts Express
https://www.parts-express.com/Ferro...MI37-r5vOj-QIVesLCBB39bQWNEAQYASABEgKf_PD_BwE
Attachments
Interesting the APG L11 sold by the Parts Express has 220 Gauss, same as 2 of three choices at Willy's site... but, its viscosity is 220... lower than the alternatives they sell, 500, 750 and 1000. Actually APG087 is 275 Gauss, 750 viscosity, CDF 2250 is 220 Gauss 500 viscosity, and the APG 1134 is 220 G, and 1000 viscosity. It will be interesting to see what Willy's suggests. Very interesting to do a deeper dive. I don't think I ever circled back to the Ferrotec website even after I got these packets..... frankly, wasn't able to find an alternative source for. "audio" ferrofluid at that time, other than Parts Express.... and I've no idea how or why they chose the APG L11.
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In comparison, SAE 20 motor oil has a viscosity of 125 cP and SAE 50 is 500 cP (at 20 degrees C)!
According to FerroTech, values in the 200–1000 cP range provide moderate damping.
https://ferrofluid.ferrotec.com/products/ferrofluid-audio/audioselect/
P.S. 220 Gauss refers to the 'magnetisation value' of the ferrofluid, and 220 is the correct value for a tweeter.
Learning all the time!
P.P.S. I'm at a loose end tonight!
I think though, when I send out my engine oil samples to Blackstone, the last thing I want to here from them is that I sent them ferrofluid! Interesting to see what Willy's might think the viscosity was from the factory for the B&W tweeters. I'm not sure I'd hear the difference, but I bet B&W cared when they tuned the package.In comparison, SAE 20 motor oil has a viscosity of 125 cP and SAE 50 is 500 cP (at 20 degrees C)!
According to FerroTech, values in the 200–1000 cP range provide moderate damping.
https://ferrofluid.ferrotec.com/products/ferrofluid-audio/audioselect/
P.S. 220 Gauss refers to the 'magnetisation value' of the ferrofluid, and 220 is the correct value for a tweeter.
Learning all the time!
P.P.S. I'm at a loose end tonight!
I did hear back from Will, I have to assume, the Will behind Willy's. He said that B&W has never been forthcoming as to what formula they used in any given driver. Looking at the website for the US based Ferrotec, there are many many considerations for choosing a specific fluid for a given application. I asked Will if the proper technique for choosing a ferrofluid would be trial and error with some measuring equipment to look at frequency response, trying to initiate a discussion, and I think I got too close to proprietary information. His response was that it was near useless for us to try to hit a specific target of viscosity as most people can't properly degauss a magnet to remove all the old particles, so adding new fluid will result inevitably in a more viscous result than intended. I find this a little presumptuous as I have built a jig in the past to hold a magnet and use a pressure washer to get every last vestige of ferrofluid out. It just takes some creativity..... and I'm not messing with the magnetic properties. This makes Parts Express 's choice of a ferrofluid with less viscosity than any on Willy's website as "interesting". Perhaps they are trying to cover the situation where old particles remain, so the viscosity will be higher than the fluid you're buying, closer in some immeasurable fashion to the target. No idea here. Open to discuss.
Removing Ferrofluid from a driver's gap is easy: any fabric material will suck it out as capillary forces ar much stronger than the retaining force from the magnet. If you wipe it with a solvent like kerosine or another alkan you remove 99+% of the material. After that procedure, residues that remain on the surface have no measurable impact on the driver properties when refilled.