B&W 803D crossover caps

Ptss:

I can see the potential benefit to moving the XOs outside the box. My early JBL L212 had the crossovers outside of the enclosed driver housings.

Vibration from the drivers will definitely influence the inductors and capacitors in the network, simply "gluing" them to the pc board with lumps of RTV or caulk may not be that effective.

But practically speaking (no pun intended) moving them outboard of the 803D also has it's pitfalls, as you end up with longer speaker wiring between the drivers and the XO, with the accompanying increase in inductance and resistance. Not to mention the ugly appearance. The bass XO is huge, with monster 100 mFd Mundorf polypropylene bypass caps. Placing that outside would look butt ugly IMHO.

Bypassing caps...not sure what they buy you in a crossover. I know folks use them to "tweak" the sound but I have never played with them for that. I would rather buy a single cap with the right dielectric and low ESR in the first place if at all possible. Plus, from a technical viewpoint, things like dielectric adsorption cannot be remedied with parallel caps; only ESR or maybe ESL. The frequency range in a speaker crossover (maxing at maybe 30 KHz) is just not high enough to see a resonant frequency shift by using a 0.1 mFd cap in parallel with a 5 or 10 mFd coupling cap in a tweeter XO, for example.

So for example, the B&W diamond tweeter is crossed at 3500 -4000 Hz. The reactive impedance of the 4.7 mFd coupling cap at 4KHz is about 8 ohms. It would only be 0.8 ohms at 40 KHz! The 4.7 Mundorf has an ESR that is about 10 milli ohms or .01 ohms, still 10 times lower than the capacitive reactance at 40 KHz. Now what good is placing a 0.1 mFd cap in parallel with the 4.7? It would have a capacitive reactance of 50X the 4.7 (at 40 ohms) and who cares what its ESR is, because that would be swamped with the capacitive reactance.

If you are parallel connecting a series of lower value caps that may make sense if you cannot get the total value in a single cap (like a teflon or polystyrene, for example).

Hi, my experience might be of some help if you want to upgrade the 803D2, which is what I've done. I did buy a new set of Sonus Faber Olympica III, and wanted so much to replace my 803 (or to be honest, my wife wanted to replace my 803...) The SF midrange was to die for, but the same cannot be said about the tweeter and bass. To make a long story short, I sold the SF after upgrading the X-over in the 803.

The 803 suffers from; some light upper frequency enhancement with the tweeter, and some nasality and "in the box" sound from the Kevlar midrange.

When going through the x-over (B&W had kindly posted the schematic on their homepage), it was obvious that the 47uF MKP Mundorf and the industrial resistor in series with the midrange was a week point. I knew also that the 5,1uF Mundorf Supreme SGO combined with tweeters easily can highlight the upper frequencies, too much in a not optimal set up.

I first replaced the 47uF with the new EVO MCap Alu oil and put in a Duelund Silver CAST resistor. I also replaced the 10uF Supreme Oil in parallel with Supreme SGO.

It took some hundred hours to burn in the new setup, but the result was very satisfying. In brief, a much larger soundstage, the in the box sound was 75% reduced, the bass(!) was indeed punchier, 3D stage in all direction had grown. At the same time, there were some highlighting of the upper midrange that was not to my likings. I therefore decided to replace the EVO MCap with the new Supreme EVO Oil.

At the same time I decided to replace the 5,1uF with a Duelund Copper CAST to see if I could get more from the tweeter.

It now needed some 500 hours to sound OK, and after around 700hours, it was confirmed, not only was the midrange free from any kind of boxiness, it was also the best sounding midrange I've experienced so far in my home. The tweeter together with the midrange now sounds like a Stradivarius with all I can wish for regarding holography and texture.

I have listened to the new 805D3 in two different setups. The first did impress me deeply. They had the speed and holography like never before. In the second set up they did not impress me at all, just telling me that the surrounding is just as important as the speaker themselves. I did like the speed and holography, but they did not have the texture as the 803 now has.

With the speed from the 805 in mind, I decided to replace the MKP for the bass drivers as well, this time with the fantastic resistors from Pathaudio and Mundorf EVO Alu in oil.

This time the upgrade gave me some more macro dynamic, but not as much as I had hoped for. It seems like the driver themselves are the bottleneck here.

There is space for the upgrade behind the Kevlar driver, but you have to reorganize X-over a bit. For those how want to see how it can be done, just send me a mail, s-b-o@frisurf.no.

I'm very happy I sold the Sonus, the sound from the 803 betters them in every aspect, and this with a great margin. I've of course considered the new 804D3, but I'm not sure they will better the fantastic texture, bass and resolution from the 803. Be aware, they use MKP, electrolyte and not the top of the line Mundorf capacitors. They have also started to bypass the capacitors with smaller values. I've never succeeded with this little trick in my x-overs, for power supplies, yes, but not in loudspeakers.

The 803D3 are too expensive, and since I've now started to upgrade of the 803, I've ordered the new Continuum drivers to replace the Kevlar. Still waiting for the drivers to arrive.

My experience tells me, there is lot more to get from the 803 with better components, and it is a shame that B&W has not offered a signature model with these upgrades incorporated already!

(To bad I cannot show any photoes here in the Forum)

Stoni:

Interesting post. I have been looking at what B&W has been doing with these cross overs in the last few product iterations. Particularly with the capacitors, they have been all over the map, except with that 47 mFd MKP, which is consistently used from the 804S through the 803D2/3.

In my 803d (first diamond in the series), the tweeter coupling cap is 4.7 mFd Mundorf Silver/Gold Supreme (not oil). In the 803D2, they went to Supreme Oil (Al metallization?), not Supreme Silver/Oil or Silver/Gold/Oil. Looks like in the D3 they are using Supreme SGO at 5.1 mFd, not 4.7 mFd?

I have decided to try the EVO SGO 47mFd in the midrange. The Al/Oil is cheaper but I prefer silver metallization. I have also decided to replace my Supreme 4.7 mFd S/G with a Supreme 4.7 mFd SGO. If that is too strident, I will consider a Jupiter copper paper/oil, but I am nervous about the longevity of these paper/oil caps (along with the cost).

I also have a pair of 804S, with the Al tweeter. That product uses almost the same values as the 803d. The tweeter coupling cap is Mundorf 4.7 mFd Supreme, and the midrange (which is the same unit as in the 803) is coupled with that MKP 47 mFd, and bypassed with a Mundorf Supreme 10 mFd. Like the 805, the bass drivers are bypassed with an electrolytic parallel with a film (150 mFd electrolytic parallel with a 47 mFd MKP film). In the 803D, the bass drivers are bypassed with two 100 mFd MKP films.

I agree with you that bypassing an electrolytic with a film in a cross over is not a good idea. I think that is because in a XO, the caps see significant AC voltages. Any dielectric adsorption effects in an electrolytic cannot be reduced by a film in parallel, and may therefor may be audible.

I use the Jupiter copper caps and have never had an issue. You will never have an issue in a speaker crossover as there is no heat. Heat is the only factor of concern with these caps. I use them in tube amps with heat and still no problems. 

I have had them in my speakers and gear since they were introduced perhaps two years ago. So much better than any Mundorf caps based on my considerable cap rolling experience.  They are far more quiet, they remove noise better than the Duelund CAST. They are SOTA for micro details and exhibit a nice airy, natural tone. I prefer them to Duelund as they are more neutral through the upper mids. Very special cap. 

Over the last few days I have had a chance to complete the mods to my crossovers. Thanks to all for their suggestions.

I had to remove the upper bass driver and the mid range FTF driver to get at the crossovers and the wiring. I also removed the tweeter but I will get to that challenge below.

The XOs are mounted on plastic standoffs that are a bear to release the PC boards from. B&W slops glue on top of the barbs that hold the boards to the standoffs, and getting all the glue from the barbs usually means destroying the barbs. I contacted B&W and their CS was kind enough to send me back ups (they are not listed in their parts lists). I ended up pulling the two front standoffs and replacing them with a threaded insert designed for wood. My local hardware store had some that fit the .280" holes perfectly (use 5/16", for #8 screws). With .25" tall spacers, these mounted the boards perfectly.

The HF XO board is mounted on the roof of the midrange chamber, the MID XO is mounted on the floor. To remove the HF XO you have to release the board from the standoffs, then cut a number of tie wraps to release all the wiring. The HF XO is fed with two 12 ga wires (red/black) terminated in gold plated tab connectors (nice). Another pair of 12 ga black/red are soldered to this board and are terminated in a Molex connector that feeds the tweeter. I did find many of the tab connectors to be very loose, so I had to correct that before re-connecting.

I ended up swapping out the Supreme SG 4.7 mFd for an identically sized Supreme SGO. I also pulled the 0.5 OHM tab power resistor (no name on it) and replaced it with a 0.75 OHM 1% 100W MP9100 Caddock thick film resistor that mounted to the OEM heatsink perfectly. I used 0.75 OHM instead of the 0.5 OHM to reduce the tweeter output slightly. B&W originally spec'd a 1.0 OHM which they changed mid production to 0.5 OHM.

For the MID XO, I also swapped out the 2 OHM resistor with a 2.0 OHM 1% Caddock MP9100. I pulled the MKP 47 mFd Mundorf film cap and replaced it with an EVO SGO 47 mFd. This cap also fit quite nicely. I had PartsConnex match a couple to under 1%.

After re-mounting the XOs, I soldered all the gold plated tab connectors to the wire they were crimped to. Unusually, some were soldered by B&W and some were not. B&W also used some sort of grease on the connectors (not necessary for gold connectors IMHO) so I removed that as well. I pulled all three bass drivers to tighten and solder connections.

Now the tweeters. I strongly suggest most users leave these guys alone. They are extremely fragile and you must not touch that diamond diaphragm if at all possible. In mine, I felt a little too much front to back play, so I thought something might be loose. The motor unit/diaphragm is coupled to a bar that runs rearward through the end of the casing tube. At the end of this bar, a soft, gooey gasket material (looks like Sorbothane with the consistency of a gummy bear that has been on a hot sidewalk) surrounds the bar and isolates it from the casing. When you pull the motor and bar forward, you inevitably destroy this gasket as it sticks like crazy to the bar, and turns itself inside out as you pull forward. So order a backup from B&W before you disassemble the guts of the tweeter.

In my tweeter, the plastic coupling nut that holds the bar to the motor was loose. And you cannot tighten this nut unless you pull the guts of the tweeter out.

After all was put back together, I had a chance for some preliminary listening. I have to say the total end result was more pleasing than I anticipated. If I have to use a single word, it would be "smooth". Edginess on horns and vocal sibilants was gone. Bells and symbols are now slightly recessed in volume, but still very clear in position, with more 3d space between them. The overall sound fill left to right is vastly improved, with sound spilling outside the boundary of the left and right speakers (something I have been struggling to get with these 803d's for some time). The midrange seems to be separated better from the bottom end in clarity (this is hard to describe), so the bass transients no longer "mask" some of the midrange, as they had done before.

All in all, I am very happy with the changes.