Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Multi-Way Conventional loudspeakers with crossovers

Recap B&W Matrix 2 1986 issues
Recap B&W Matrix 2 1986 issues
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 13th January 2018, 02:40 PM   #11
eriksquires is offline eriksquires  United States
diyAudio Member
 
eriksquires's Avatar
 
Join Date: May 2013
Hey K!

Well, it seems to be "optimized" so they can play very well with tube amps. To do this they attempt to flatten the impedance curve. There are three sets of components that run in parallel to, and before the filters. A Zobel (CR) and two resonant circuits (CLR).

The tweeter circuit also has a time-alignment component. That's the pair of 0.49uH inductors crossed with 20uF caps. Lastly, there's a protection circuit, which has the diodes, relay and transistors (I would probably remove this entirely).

Also, the drawing order is quite odd. Inputs on the right, but then flow left before coming back right.

The filters themselves are extremely simple.

Best,

E
__________________
All of my successes and failures can be explained by my attempts at getting a girlfriend. All of them.
  Reply With Quote
Old 13th January 2018, 03:10 PM   #12
eriksquires is offline eriksquires  United States
diyAudio Member
 
eriksquires's Avatar
 
Join Date: May 2013
So did a little plugging around. I used the default 8 ohm perfect drivers to stand in, and I examined the power dissipation of the 3 impedance lowering circuits. Sorry I did not keep the same part designations, but you'll see them in the top left of the attached schematic.

Recap B&W Matrix 2 1986 issues-bwmatrix_schema-jpg

I then set the amplifier to 50 watts output. Obviously, continuously this is actually a lot, but it's helpful to see what's going on. Look at the power dissipation of R1, R5 and R2.

Recap B&W Matrix 2 1986 issues-bwmatrix-jpg

This seems almost careless. Due to the resonant nature of the circuits they are attached to, R5 and R2 (on my schema) will have almost 30% more power through them than input! The original 11 watt rating was WAY too low. What I suspect happened is that the heat from the resistors fried the caps. So you are left with a dilemma. You should probably use about 2x that (minimum) but.... the problem is they will still dissipate that heat! Meaning, you have to find some way to keep the resistor heat away from the caps or you'll repeat the problem.

I really would not rebuild these as-is. Leave all three out, and measure the impedance using DATS or Room EQ Wizard (or whatever your impedance measurement tool of preference is) before thinking it is worthwhile. It may very well be that these three circuits don't do a thing for you.

Edit: After further analysis, it may even be possible to rethink the circuits, and come up with values that dissipate much less power, but again, not sure these circuits are worthwhile for solid state amps.

Best,


E
Attached Images
File Type: jpg BWMatrix_schema.jpg (49.5 KB, 112 views)
File Type: jpg BWMatrix.jpg (131.3 KB, 109 views)
__________________
All of my successes and failures can be explained by my attempts at getting a girlfriend. All of them.

Last edited by eriksquires; 13th January 2018 at 03:21 PM.
  Reply With Quote
Old 13th January 2018, 03:51 PM   #13
eriksquires is offline eriksquires  United States
diyAudio Member
 
eriksquires's Avatar
 
Join Date: May 2013
Not awake yet. 80 W / 50 W = 60% more power! So basically with about 7 watts of power you will fry those resistors.

The lower resonant circuit is tuned to 50 Hz, where there is a great deal of energy in the bass. I'm honestly surprised these speakers lasted as long as they did.

Best,


E
__________________
All of my successes and failures can be explained by my attempts at getting a girlfriend. All of them.
  Reply With Quote
Old 13th January 2018, 05:22 PM   #14
eriksquires is offline eriksquires  United States
diyAudio Member
 
eriksquires's Avatar
 
Join Date: May 2013
Thanks to Wolf posting on the Parts Express forum, I was able to find another thread here at DIY which discusses the crossover, especially the protection circuitry, and a related crossover the Matrix 3:

Could a kind soul please break down this horrid Xover

I did not see the power simulations that I have here however. But you can see the flat impedance curve. This idea does not seem to have lasted very long at B&W. I can't find evidence of it being used much before or after. I strongly suspect they were going after the mid-power tube market with this series of speaker. Take for example a much more recent 800 D:

Click the image to open in full size.

As you can see, any pretense of flattening the impedance curve is gone.

Best,


E
__________________
All of my successes and failures can be explained by my attempts at getting a girlfriend. All of them.

Last edited by eriksquires; 13th January 2018 at 05:26 PM.
  Reply With Quote
Old 14th January 2018, 08:06 PM   #15
MTH444 is offline MTH444  Belgium
diyAudio Member
 
Join Date: Jan 2018
Location: Limburg
ok, Iwill replace them with the same make. Isit a problem if the voltage of the electrolytic caps is higher than the originals? Now they are 50V, can I replace them with 100V ones?
  Reply With Quote
Old 14th January 2018, 09:11 PM   #16
eriksquires is offline eriksquires  United States
diyAudio Member
 
eriksquires's Avatar
 
Join Date: May 2013
Higher voltage is fine, but as I wrote, the real problem is the heat of the resistors. Double the wattage, and try to place the caps so they are no longer near them.

If you cannot separate the resistors and caps, increase the temperature rating on the caps, by a lot. If you have 80C or 85C try to get 100C caps.

As I wrote though, I think they are unnecessary unless you are using a tube amplifier. I'd actually just remove them entirely.

Best,

E
__________________
All of my successes and failures can be explained by my attempts at getting a girlfriend. All of them.
  Reply With Quote
Old 15th January 2018, 08:21 PM   #17
MTH444 is offline MTH444  Belgium
diyAudio Member
 
Join Date: Jan 2018
Location: Limburg
Do you mean remove al the caps? Or what do you mean? I tought the caps are needed for filtering the right frequencies.
The resistors are now 11W. I can replace them by 25W resistors, I want to mount them to the pcb with a gap, so they dont damage the pcb if overheated. (that is wat happend before.
  Reply With Quote
Old 15th January 2018, 09:06 PM   #18
Lojzek is offline Lojzek  Croatia
diyAudio Member
 
Lojzek's Avatar
 
Join Date: Feb 2012
Location: Croatia
Consider mounting resistors on a piece of a heatsink.
__________________
A good dialogue makes you feel like a changed person, not like you have won or lost the competition.
  Reply With Quote
Old 15th January 2018, 10:31 PM   #19
eriksquires is offline eriksquires  United States
diyAudio Member
 
eriksquires's Avatar
 
Join Date: May 2013
Hi MTH!

That's what I'm saying. Those 2 very large caps (100uF and 1,000uF) are not part of the frequency filtering.

They are there to make life easier for tube amps. If you aren't running tube amps, you may put them in the trash and forget about them. This style of design kind of came and went. In 5 more years, B&W would not have put those parts in at all.

+1 for Lojzek's idea, is to get heat sink mounted resistors if you MUST restore them.

Bet,

E
__________________
All of my successes and failures can be explained by my attempts at getting a girlfriend. All of them.
  Reply With Quote

Reply


Recap B&W Matrix 2 1986 issuesHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
1986 Sony CFS-280 Mini Boombox (pics) Robcrx The Lounge 7 29th September 2014 02:48 AM
NOS 1986 Mitsubishi CVX-3 Amplifier Robcrx Car Audio 0 15th March 2013 03:09 PM
Elektor Top of The Range Preamplifier 1986-7 audiophilo Elektor 3 17th December 2011 05:23 PM
scott 222 recap issues ihscoutlvr74 Tubes / Valves 7 25th January 2008 07:37 PM
Discrete Class-D anno 1986 Baldin Class D 11 26th October 2006 07:30 PM


New To Site? Need Help?

All times are GMT. The time now is 03:15 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki