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B&W 803D crossover caps

I am considering an upgrade of the crossover capacitors in by B&W 803Ds, particularly the mid and HF coupling caps.

I took out the top bass driver to find out what caps were installed. It looks like for the diamond tweeter B&W uses a Mundorf Supreme silver/gold, 4.7 mfd 1200V. For the mid driver there are two; a 47 mfd Mundorf MKP 400V series coupling cap (in series with the driver) and a 10 mfd Mundorf Supreme siver/gold bypassing cap (parallel to the driver).

I was thinking about changing out all three, but have a few concerns.

I was going to replace the 10 mfd, 4.7 mfd Supreme silver/gold with Supreme silver/gold/oil. Would there be enough of a difference in these two types to justify the cost? I also do not want to make the upper end any brighter.

I am also concerned about the long term reliability of oil filled caps, as some failures have been reported in warmer environments. I wonder if B&W did not use the silver/gold/oils for that reason.

The biggest impact I suspect will come from the replacement of that series 47 mfd MKP. I would probably use either the Mundorf MCap EVO (Al metalization), MCap EVO oil (Al/oil), or the MCap EVO silver/gold/oil. All three are the same size for 47 mfd, and will fit to replace the MKP. Barring the issues about oil, which might be the best sounding? Again, I want to avoid too much enhancement of the upper midrange.
dhl93449
georgehifi's avatar
georgehifi
10,312 posts
 
(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
biggy79
64 posts
 
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
biggy79
64 posts
 
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
dhl93449 OP
455 posts
 
biggy

That is what I did. Silver gold Oil 4.7 uFd for the coupling tweeter; 47 uFd EVO SGO for the mid coupling cap; SGO 10 uFd for the mid bypassing cap.  
Whether you use SGO or just "oil" (those are aluminum metallized instead of gold/silver) is a matter of personal taste (and budget). I never found SGO "harsh" or "bright". Maybe you can try the "oil" version first, since they are much lower cost. I just think the silver/gold metallization is lower impedance since gold and silver are much better conductors, but the aluminum may be applied by Mundorf in a thicker layer, which compensates for lower conductivity of the metal itself. Specs wise I don't think there are major differences, but longevity wise I think the gold/silver are better.
As far as the resistors go, you will have to see exactly what B&W put in your crossovers. As I said, they vary by production year and model. I substituted Caddok MP9100 series for the versions used by B&W; they are a pin/pin exact replacement, and fit in the pc board holes (and on the heatsink) precisely. I would avoid the exotic resistors that will not fit on the pc board. Running long wires to mount these can undo the benefits of them in the first place. Plus, you need to replace the OEM parts with versions that have the same or better power rating.
dhl93449 OP
455 posts
 
biggy:

Regarding sizes. Check a website like parts connextion. Not all "EVO" sizes are the same, and the "Supreme" (black) versions are larger I think. I used the " 47 uFd EVO silver gold oil", in the white cases with gold printing. The "Supreme" versions have special, non-inductive windings and are therefor actually two caps in the same package, therefor much larger. I don't think a EVO Supreme SGO is available at 47 uFdf. 
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