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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
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. 
dhl93449 OP
455 posts
 
George:

Regarding parallel caps. I agree in general, except when there is no or limited choice. For example, when an Al electrolytic is used as a coupling cap at the output of an amplifier driving low impedance loads. A polypro or film cap may not be available or practical to use in that application if DC offset from the amp is an issue. Adding a parallel poly pro film cap will definitely improve the sound over just an electrolytic alone. 
I believe one reason that parallel caps are not a panacea is that certain properties (like poor dielectric adsorption) cannot be compensated for by placing caps in parallel. 
One practitioner of massively paralleling film caps (John Curl of Parasound) has recently commented that that practice (seen in many early Parasound power amps) may not be best. He cites resonance effects between these parallel stacks at extremely high frequencies (100's of Megahertz) as the issue. Those early power amps still sound pretty good though.
georgehifi's avatar
georgehifi
10,312 posts
 
For example, when an Al electrolytic is used as a coupling cap at the output of an amplifier driving low impedance loads.
This kind of amp cap coupled output is very rare to have. I take it it’s tube with no output transformer, but with capacitor coupling instead, I would just get an OTL myself but??

For and 8 ohm speaker you would need at least 2000uF for the coupling cap to see low fr limit of -3db at 10hz.
One or a couple paralleled depending what polarizing output voltage this amp has of these would fine great with NO! bypass cap.

https://hfc-fs.s3-eu-west-1.amazonaws.com/s3fs-public/audio-note-electrolytic-update-051217_0.pdf
or you could get cheaper Black gates instead.
https://www.hificollective.co.uk/components/black_gate_n_type.html

Cheers George
biggy79
64 posts
 
@dhl93449

I found here http://www.audiokit.it/it/30951-condensatori-mundorf (I am from Italy) there is a 47uF Supreme EVO Oil, which measures 76x67 mm.

The 47uF standard M-Cap EVO Oil measures 50x50 mm, the same as your EVO Silver Gold Oil.

Do you think the extra 26mm thickness of the Supreme Evo can make it not fit in?

Maybe if Stoni (see the 12-09-2015 10:27pm post) could use the Supreme EVO Oil into his 803D2 the same could happen in our 803D ...

The M-Cap Evo Oil is available at 100uF, so if I use the EVO Oil in series with the midrange maybe I could put woofer and midrange (coupling) caps of the same type (like in the original project!) even if you told me woofer caps don’t make significant difference in sound, but there would be a theorical coherency between bass and mids, both with EVO Oil instead of MKP, and the same thing would happen between mid (bypassing) cap and tweeter (coupling) cap, both with Supreme SGO instead of Supreme SG.

I am also thinking of removing all silver from my speakers, and "downgrade" from the Supreme SG to the standard Supreme for coupling tw cap and bypassing mid cap: warmer, richer and more natural sound, with absolutely no emphasys on the treble and upper midrange.

Maybe If I do, I would transform the B&Ws in other speakers and I don’t want to, but I would be happier.

Hard choice

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