Recap B&W Matrix 2 1986 issues

[MTH444]

In 1986 I bought a pair of B&W Matrix2 speakers and had a lot of fun with them. Until... one day they smelled like something strange was burning.
A capacitor of 100µF and a resistor of 4ohm where burned on both speakers and burned the pcb locally. I brought them back to the store where I bought them, and they guy who sold them to me tried to repair them, but had not the right capacitors of 100µF, so he put in the left speaker 12+85= 97µF and in the right one 15+82= 97µF. For the resistor he used a different value.They worked, but i felt not happy with it. Now so many years later I want to repair them properly.

- what make are the best capacitors to use? (original is ALCAP)
- must I also recap the RCL PMT/2R capacitors?
- some of the smaller resistors are oxidized, must I also replace them?

I'm new on this forum. So if somebody can answer my question would be great.
Many thancks in advance.

PS: I use a Kenwood KA1100SD to drive them. I think this amp is to powerfull for them.

Mike

[djk]

Premium Audio Grade Components | ERSE

[eriksquires]

B&W has become a Mundorf shop, so if you want to stick with the factory choices, I'd go with that. MKP is the least expensive, and also smallest for the overall size.

I like the Mills 12W resistors. They are great sounding, and small for the wattage. Make sure you leave plenty of space around them so they ventilate properly.

Best,

E

[MTH444]

must I also replace the RCL PMT/2R capacitors, or do they not age?

eriksquires: what do you mean by Mundorf shop, do they use mundorf capacitors now?

thanks for the replies

[giralfino]

If the original cap is electrolytic (ALCAP is), buy an electrolytic, you are effectively restoring the original spec and sound. Moreover you'll find rather difficult to accommodate a film cap in a space designed for an electrolytic. Note that the repair done was probably effective because 97uF is equivalent to 100uF once you factor in the caps tolerances.

For the RCL PMT/2R caps, as they are film caps, they don't age so there isn't any reason to replace them.

I would replace also the resistor that was changed after the burn because it is not the original value, and restore the original 4R value.

Ralf

There is not a too powerful amp, in fact the opposite is true: you risk to damage a speaker more easily from an underpowered amp driven to clipping.

[eriksquires]

MTH444 - Yes. All the mid to high end B&W speakers use Mundorf film caps exclusively, but I do not know which electrolytics they use.

Erik

[giralfino]

From the photo I’ve seen this is not true for the Matrix 2, that speaker hasn’t any Mundorf cap. You can easily find the service manual: http://bwgroupsupport.com/downloads/...rix%202-TM.pdf

Ralf

[eriksquires]

Yeah, back in 1986 I don't know if B&W used Mundorf parts at all. They do a lot now though.

Best,

E

[eriksquires]

I looked at the schematic you attached. Maybe someone else will chime in here, but those big caps aren't even needed if you are running a solid state amp.

It seems they are all part of an impedance moderating circuit, and should be safely removed completely. This is why they overheated as well. Reducing impedance means they were subject to a lot of current.

Of course, you should still check your amp outputs for evidence of DC, but I would be very much tempted to run without them. If you want to see what happens without them, I'd suggest getting DATS or Room EQ Wizard (free but need a jig) and measuring the impedance of each driver, and simulating it all in XSim. You'll better be able to tell what's going on when you look at the transfer function and the impedance charts.

Best,

E

[Keruskerfuerst]

Strange crossover....