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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

Showing 9 responses by georgehifi

georgehifi's avatar
georgehifi
10,312 posts
 
You can paralell caps of the same brand at near the same value with no problem at all. In fact, this method is used my some very high end builders for the best sound.
Yes this is the only time to do that with caps in the signal path as I said previously.
And yes it "can" even be beneficial as  2 3 or 4 paralleled caps will have a lower esr than one cap of the same make and value. BUT!! the lower esr means that driver will have a slightly louder presentation due to the lowering of series resistance. So the voicing of that driver will change to what the manufacturer designed it to be and this should be taken into account.

Cheers George
georgehifi's avatar
georgehifi
10,312 posts
 
I avoid doing this most of the time in crossovers. There are some proven combos, but in general they can sound phasey and strange.
"Phasey" An even better description than my "smearing", an overlap of two different cap sounds and time constants doing the same job.

Never bypass caps in the signal path.!! Use the best quality single or two or three if you need them that big identical paralleled ones you can find.
Leave the by-passing only to power supply and V rail de-coupling caps.

Cheers George
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
georgehifi's avatar
georgehifi
10,312 posts
 
Phasey??? WTF is that?
You have no idea, if you don't know what we're talking about, then continue to bypass your signal caps and you'll never know because you obviously can't hear it.

Cheers George
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
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
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
georgehifi's avatar
georgehifi
10,312 posts
 
dhl93449

There is nothing wrong with this xover in the quality of it’s parts, look elsewhere for your upper midrange brightness.

As for the suggestion of by-pass caps, don’t! The only time to use by-pass caps is with power supply caps (decoupling), never with a cap in series with the signal or in xovers (coupling), as the two different time constants of the caps will have a smearing effect in that region that they are working in and actually degrade the sound, always use one good quality cap, and that is what B&W have done here.

https://img.usaudiomart.com/uploads/large/934237-bowers-amp-wilkins-bampw-803-diamond-803d-mf-crosso...

Cheers George
georgehifi's avatar
georgehifi
10,312 posts
 
There's no cheap caps on the mid xover I just linked to, Mundorf and M-Cap!!! and no 47nF there is a very good quality 47uF.
 
One good cap of the correct value that B&W worked out that's it, if you look at the 802D MkII photo I linked to of the mid, they have already used very good caps, I have no doubt the tweeter would be just as good if not better. 

Cheers George
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