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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
 
" 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??"

Not as rare as you think. Did you know the Bryston BDA-1/2/3 all have Al electrolytic (surface mount) coupling caps in their outputs? Along with I think their preamps, even current production. Their engineers are concerned with the small amount of DC offset their class A discrete amps produce (10 - 20 mV), ergo the caps. Using a 10-30 uFd film coupling cap is out of the question for them, as it's size and cost would be prohibitive.

Bryston does not parallel a film cap with these Al Elct caps in the output stages, due to the lack of compact surface mount film versions (poly pro are very rare in surface mount), and NPO ceramics are outrageously expensive. 

In my new BDA-3, I removed the Elect caps and put in a surface mount shorting bar. The small DC offset is easily handled by my Parasound JC2 preamp and its DC offset servo controllers. Made a significant difference in sound quality. I have been in contact with Bryston Eningineering and urged them to put in DIP switches so that users have the option of shorting out those caps if they have downstream circuitry that can handle the offsets. 


georgehifi's avatar
georgehifi
10,312 posts
 
Not as rare as you think. Did you know the Bryston BDA-1/2/3 all have Al electrolytic (surface mount) coupling caps in their outputs?

I said amps, they are preamps, and yes many preamps and sources are cap coupled, but they don't need anywhere near the size cap an amp does so one only good quality film cap will do them, again never by-pass them.

Cheers George
dhl93449 OP
455 posts
 
George:

You miss the point. I just explained that film caps are often not an option when the manufacturer is using surface mount technology for the components. Plus, the proper size poly pro film cap will physically not fit in a 1U chassis and is extremely expensive to boot. Polyester (mylar) caps are smaller, but are not as good as polypropylene.

dhl93449 OP
455 posts
 
biggy:

I am currently using all Silver Gold Oil Mundorfs; either Supreme versions (TW coupling, MR bypassing) or EVO (not Supreme) versions (MR coupling), except for the bass LF crossovers, which are bone stock. As mentioned, the harshness I believe is from the FST MIDRANGE, not the tweeter. If you want to de-emphasize the tweeter, you can increase the resistor in series with it. Replacing that MKP 47 uFd with EVO oil or EVO SGO will make a major difference, so I would start there and then listen to the results. I would not go in and wholesale replace multiple caps and resistors. Adding the anti vibration weight from the 800/802 can make another significant difference. You can see this in the midrange driver replacement video on the B&W parts website.

I put little importance into those cap reviews that rate plain "oil" with Al metallization with silver or silver/gold. Too many variables that may or may not apply to my personal system. When I have compared oil vs SGO in preamp outputs and DAC outputs, I have always like the SGO. 


As I said, try the "oil" versions first and see if you like them. They are the cheapest version and if they are better for you than SGO, then you are ahead of the game. But be aware that swapping these caps is not easy, and pulling and re-installing the crossovers is time consuming.


georgehifi's avatar
georgehifi
10,312 posts
 
George:

You miss the point.
Sorry no you confused the discussion, you said amp (see below) and I said amp and then you bought preamps into it. Most of us with the knowledge know that many sources and pre’s have much smaller coupling caps than what would be on the output of an amplifier.


"For example, when an Al electrolytic is used as a coupling cap at the output of an amplifier driving low impedance loads."

As I responded to this statement of yours. Nothing to do with preamps.



Cheers George
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