B&W 803D crossover caps

georgehifi:

I don't think I suggested there is a quality issue with the parts in the crossover, but a cheaper MKP version will not sound the same as a Silver/Gold/Oil. That is why they make the SGO in the first place. Do you even have 803Ds or have listened to them?

Replacing that MKP 47 uFd with a SGO did make a significant difference in sound quality. Neither capacitor sounds "bad", but the SGO sounds better, and isn't that what we all strive for? If every manufacturer had the tuning of their product perfect out of the box, then there would be no upgrade market then, would there?

Since my original post I have added a few more mods. I now believe the upper midrange harshness that sometimes is present is sourced from the FST midrange driver. There is a mod that the 800/802 series had (a heavy cast iron weight attached to the back of the FST driver) that is absent from the 803 series. When I asked B&W tech support why the 800s have this but the 803D does not, they told me the weight will not fit in the 803 cabinet, but it will fit in the marlan cabinet on the 800/802. So not entirely believing their story, I ordered two to see if I could fit them. I had to remove a small pc of 1" of foam at the back of the cabinet (so tech support was correct) and the drivers and weights fit fine. You have to make another threaded tension rod (I used 6mm stainless threaded rod) and obtain a couple of 6mm SS nylok nuts; one set to attached the rod to the FST driver, and another set to hold the weight snugly against the back of the driver. Don't forget there is a rubber gasket placed between the weight and driver. You may also need loktite between the threaded rod and the FST driver to keep things tight and to prevent loosening. This mod also worked quite well in smoothing the upper midrange even further.

What I would really like to get a hold of next is the latest version D3 midrange driver. They are completely different from the older FST and from what I understand, have addressed many of the problems of the earlier version. But, they are not available on the B&W parts website yet (maybe the never will be).  

biggy79

I don't think george reads your posts carefully. You are correct, there is a 'bypassing" cap (ie one parallel to the FST driver) in the crossover network. It is a Mundorf silver gold or silver gold oil, depending on what product you have or version of crossover. It is an upgrade (at least according to Mundorf, who makes these capacitors) over the any MKP version, which is in series with the FST driver.

The EVO versions are the only ones that will fit (47 uFd) as a substitute for that MKP 47 uFd. They will improve the sound considerably, although at very high cost. I do not understand, from a sound quality perspective, why B&W would use an MKP version instead of an EVO (either oil or SGO). From a COST perspective, perfectly understandable.

Don't forget the series coupling resistors in the MR CR network. The service manual shows a couple of values being used (and mine had even different values). Plus or minus 0.5 ohms in this coupling resistor can make a significant difference in the 800-1.2 KHz region.

The changes from 47 to 51 uFd in the D2 may not have anything to do with "smoothness", but a shift in crossover frequencies due to driver changes from previous versions. 

With respect to the "woofer" caps (there are two MKP 100 uFd in PARALLEL with the four drivers), remember these are there to roll off the bass drivers at higher frequencies. I don't think Mundorf makes 100 uFd SGO caps, and as these are there to attenuate signals across the woofers, their impact on sound quality is minimized (unless you have an lower midrange peaking problem). My tests with pink noise do not show any such peaking (nor do I hear one), so I leave these alone. I have heard of people "bypassing" these with lower value (like 1-10 uFd) SGO type caps, but I doubt if you gain much, because the frequencies (and impedance) needed to impact bass drivers. For example, a 10 uFd cap will be lower than 4 ohms at frequencies above about 4 KHz. That is quite a bit higher than the 200 Hz cross over frequency for the bass drivers, so these bypass caps will have little to no impact on the bass drivers at or below the crossover frequencies. 

george- download a version of the service manual from B&W and check out the crossover schematics before you comment.

There are various differences in the tweeters in the 800/802/803 series products. Whether some sound "better" than others may be a matter of personal taste or sensitivity.

(there are two MKP 100 uFd in PARALLEL with the four drivers)

Two cap of the same paralleled in series in the signal path is fine, as both are identical as both have the same time constants.

It only becomes a problem when the two are different values or makes, as both are behaving differently at a certain frequency.

EG:
A series cap 20uf seeing an 8ohm load will roll off -3db at 1khz and go out to beyond many mhz.
A series cap 2uf seeing an 8ohm load will roll off -3db at 10khz and go out to beyond many mhz
If the 2uf was use to by-pass the 20uf both will be letting through the frequencies higher than 10khz at the same time creating smearing effect because each have different sound characteristics.

I have proved this to myself many times, with caps in series with the music signal.
  
The only time a bypass cap should be use is in power supply decoupling.

Cheers George

Sorry, I used "nF" instead of "uF".

@dhl93449

Do you like my project (to "add oil" to the 4.7uF TW coupling cap and to the 10uF MR bypassing cap -since I have 803D, not 803D2- and to replace the 47uF MR coupling cap with the Supreme EVO Oil) ?

What differences could I expect using Supreme EVO Silver Gold Oil instead of Supreme EVO (Aluminium) Oil in the MR?

What values for TW and MR resistors do you suggest?

Ok, I will keep the MKP caps on the bass section.

Many thanks

Wait a minute, maybe I have misunderstood some things:

- does the Supreme EVO Oil not fit in the MR crossover?
Can I use only the standard EVO Oil?

- in the D2, the 10uF bypassing cap is  "Supreme Oil" ... is it a custom model only for B&W speakers, not on the market?

Anyway, my 803D uses Supreme Silver Gold (without oil) both in series with the tweeter (4.7uF) and in parallel with the midrange (10uF).

Replacing both caps with Supreme Silver Gold Oil should give more smoothness and refinement  without changing too much the original project, I guess.

Replacing the MKP 47uF coupling cap in the MR crossover  with the EVO Oil (not the Supreme EVO Oil ?) should give a GREAT improvement in mid frequencies.

@dhl93449  tell me if now I am right