DM6 Recap

makepeace · 24th June 2011, 08:36 AM

Hi guys,

I have an old set of B&W DM6's that I'm refurbishing. The one tweeter was blown, so I've bought a set of TW26's for cheap that I'm going to put in which are on the way to me now from Holland.

Next thing, when I tested these loudspeakers out a while ago on my Sansui AU 4900, something was pushing the amp into protect mode when I turned the volume up around 10 o'clock. Is it likely that the capacitors in the DM6's have deteriorated causing their reactances to drop slightly, thus decreasing the total impedance which results in drawing too much current from the amp, pushing it into protect mode?

Anyway, I was planning on recapping the crossovers as a matter of course, and maybe this will solve the aforementioned problem. Here is a schematic:

So, for the pair of speakers I need:

C1 50uF x 2
C2 30uF x 2
C3 35uF x 2
C4 3uF x 2
C5/6 2.2uF x 4
C7/8 3.3uF x 4

Is there any specific voltage rating or type of capacitor that I should get? It doesn't specify in the service manual. I would guess that they are all bipolar electrolytic, in my limited experience of electronics I haven't seen nonpolar above 1uF, but I'm likely wrong.

Also, some of the values are proving difficult to find such as the 35uF. I have seen other people doing recaps on speakers, and they use a number of smaller capacitors in parallel to get close to the equivalent value. Is this accepted practice?

Thanks
Jono

makepeace · 24th June 2011, 01:11 PM

Have done a bit of looking, and I see that you do get high capacitance nonpolar. I'm looking at Solen's metalized polyester caps (the yellow ones, not the pricey "fast" caps). Would these be adequate for recapping these crossovers? I don't want to spend a huge whack of cash on caps, yet.

Andy5112405 · 24th June 2011, 01:23 PM

B&W currently use Mundorf Caps in their 68* Range of speakers.

They claim that these are specially selected for their sonic performance.

I've got a pair of 683s and I can't fault them.

DrDyna · 24th June 2011, 01:55 PM

Quote:

Originally Posted by Andy5112405

B&W currently use Mundorf Caps in their 68* Range of speakers.

They claim that these are specially selected for their sonic performance.

I've got a pair of 683s and I can't fault them.

Mundorf are probably more money than the Solen FC even :S

Andy5112405 · 24th June 2011, 02:04 PM

As there is plenty of room inside the speaker, you could try building up caps from MKSP4's which aren't too expensive. It wouldn't look pretty but, hey, its DIY and it's inside the box.

makepeace · 24th June 2011, 02:19 PM

Thanks for the replies. Have checked out some prices on the Mundorf caps, and they are definitely out of the price bracket, even the lowest range (MKP's it is? Andy, I searched MKSP4's and didn't come up with anything..)

I don't mind having to build up caps, if that is the way to go. I could use those Solens which would cost me 75$CA incl shipping. I could also use Mallory 150s for the smaller sizes and F&Ts for the larger.

Is there any objection to using a single 80uF in place of the 50uF and 30uF (C1 and C2), or are they paralleled for a reason?

Are there any voltage ratings I should adhere to for crossover caps?

Thanks

Andy5112405 · 24th June 2011, 02:27 PM

Sorry I was typing too quickly.

Have look at http:\\www.rs-online.com and search for MKPS capacitors.

Mr. dB · 25th June 2011, 01:09 AM

Quote:

Originally Posted by makepeace

Is it likely that the capacitors in the DM6's have deteriorated causing their reactances to drop slightly, thus decreasing the total impedance which results in drawing too much current from the amp, pushing it into protect mode?

This does not sound like a plausible explanation to me.

makepeace · 25th June 2011, 01:59 PM

Quote:

Originally Posted by Mr. dB

This does not sound like a plausible explanation to me.

Why not? Do you have an alternative postulation?

Andy5112405 · 25th June 2011, 02:45 PM

Having worked for and worked with B&W, I have never experienced a crossover failure. That's not to say they haven't failed but I would look elsewhere for the problem.

24th June 2011, 08:36 AM	#1
makepeace diyAudio Member Join Date: Oct 2010 Location: Hermanus	DM6 Recap Hi guys, I have an old set of B&W DM6's that I'm refurbishing. The one tweeter was blown, so I've bought a set of TW26's for cheap that I'm going to put in which are on the way to me now from Holland. Next thing, when I tested these loudspeakers out a while ago on my Sansui AU 4900, something was pushing the amp into protect mode when I turned the volume up around 10 o'clock. Is it likely that the capacitors in the DM6's have deteriorated causing their reactances to drop slightly, thus decreasing the total impedance which results in drawing too much current from the amp, pushing it into protect mode? Anyway, I was planning on recapping the crossovers as a matter of course, and maybe this will solve the aforementioned problem. Here is a schematic: So, for the pair of speakers I need: C1 50uF x 2 C2 30uF x 2 C3 35uF x 2 C4 3uF x 2 C5/6 2.2uF x 4 C7/8 3.3uF x 4 Is there any specific voltage rating or type of capacitor that I should get? It doesn't specify in the service manual. I would guess that they are all bipolar electrolytic, in my limited experience of electronics I haven't seen nonpolar above 1uF, but I'm likely wrong. Also, some of the values are proving difficult to find such as the 35uF. I have seen other people doing recaps on speakers, and they use a number of smaller capacitors in parallel to get close to the equivalent value. Is this accepted practice? Thanks Jono

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24th June 2011, 01:11 PM	#2
makepeace diyAudio Member Join Date: Oct 2010 Location: Hermanus	Have done a bit of looking, and I see that you do get high capacitance nonpolar. I'm looking at Solen's metalized polyester caps (the yellow ones, not the pricey "fast" caps). Would these be adequate for recapping these crossovers? I don't want to spend a huge whack of cash on caps, yet.

24th June 2011, 01:23 PM	#3
Andy5112405 Banned Join Date: Nov 2006 Location: Torpoint	B&W currently use Mundorf Caps in their 68* Range of speakers. They claim that these are specially selected for their sonic performance. I've got a pair of 683s and I can't fault them.

24th June 2011, 02:04 PM	#5
Andy5112405 Banned Join Date: Nov 2006 Location: Torpoint	As there is plenty of room inside the speaker, you could try building up caps from MKSP4's which aren't too expensive. It wouldn't look pretty but, hey, its DIY and it's inside the box.

24th June 2011, 02:19 PM	#6
makepeace diyAudio Member Join Date: Oct 2010 Location: Hermanus	Thanks for the replies. Have checked out some prices on the Mundorf caps, and they are definitely out of the price bracket, even the lowest range (MKP's it is? Andy, I searched MKSP4's and didn't come up with anything..) I don't mind having to build up caps, if that is the way to go. I could use those Solens which would cost me 75$CA incl shipping. I could also use Mallory 150s for the smaller sizes and F&Ts for the larger. Is there any objection to using a single 80uF in place of the 50uF and 30uF (C1 and C2), or are they paralleled for a reason? Are there any voltage ratings I should adhere to for crossover caps? Thanks

24th June 2011, 02:27 PM	#7
Andy5112405 Banned Join Date: Nov 2006 Location: Torpoint	Sorry I was typing too quickly. Have look at http:\\www.rs-online.com and search for MKPS capacitors.

25th June 2011, 02:45 PM	#10
Andy5112405 Banned Join Date: Nov 2006 Location: Torpoint	Having worked for and worked with B&W, I have never experienced a crossover failure. That's not to say they haven't failed but I would look elsewhere for the problem.