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PostPosted: Fri May 04, 2018 2:02 am 
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Hello all. I just acquired quite a nice pair of B&W DM5, made from between 1975-79. I was expecting some great things, but I'm quite underwhelmed. The sound is a muffled and dark, and the output from the tweeters (both) is very muted and quiet. I have to place my ear right up to the tweeters to hear any kind of output. 90% of the sound reproduction seems to be coming from the mid/bass driver, thus the muffled/dull sound. Upon researching the speaker, I learned that the crossover incorporates polyester caps. I realize the electrolytics can be problematic when they age, but are polyester subject to falling out of spec as well? I am hoping that the tweeters are not damaged, and that a recap would solve the problem. I know that a tech can test the tweeters, but as said, I'm hoping a recap will breathe new life into this nice little speaker system.


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PostPosted: Fri May 04, 2018 2:42 am 
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Yes film caps in crossovers dry up too, not only with vintage amps/preamps/tuners.

IMHE older B&W doesn't use anything more than average to below average quality parts in crossovers so if you use pretty much anything you'll hear an improvement. Solen caps are inexpensive and should sound fine. You'd have to spend a whole bunch more and may not hear any difference.

Replace the electrolytic caps with something affordable and leave the resistors. After all that your speakers should sing! You can always pay more for replacement parts if you can't sleep.

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PostPosted: Fri May 04, 2018 8:24 am 
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Hi,

Funny you should mention this. I just dismantled a pair of Spendor BC1s which were built around 1974. I bought $20 worth (12 caps) of new polyester capacitors fitted to exact original values. I had considered buying 'audio priced' caps but the son (Derek) of the original BC1 designer (Spencer Hughes) told me not to bother and just use mylars and polys. My bench guy measured the old poly caps as he pulled them and they were mostly off spec, by up to -.2 MF. Now that may not seem like much but even a small deviation can move the cross-over values and electrical response way off kilter. The BC1 has an exotic three way crossover - thus the need for six caps and four wound bobbins on each board.

Anyway, the bottom line is this. My BC1s sounded pretty good before and now they sound fantastic. I just got off the phone with the guy who installed the caps to thank him. They are smoother across the entire mid-range by a country mile and I can tell the cross-overs are spot on by the renewed voicing and tonal coloring. The resolution of low level detail is now even better than when they were new speakers.

I am not sure that the problems you are having are all cross-over related - but they could be, and a rebuild of the X-over on a quality older speaker system is highly recommended. It is also a good idea, where possible, to rotate the woofers 180 degrees to counteract speaker surround sag, which gravity induces and which often leads to scratchy voice coils.

Cheers,
David Neice

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PostPosted: Fri May 04, 2018 8:28 am 
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buybye88 wrote:
Hi,

Funny you should mention this. I just dismantled a pair of Spendor BC1s which were built around 1974. I bought $20 worth (12 caps) of new polyester capacitors fitted to exact original values. I had considered buying 'audio priced' caps but the son (Derek) of the original BC1 designer (Spencer Hughes) told me not to bother and just use mylars and polys. My bench guy measured the old poly caps as he pulled them and they were mostly off spec, by up to -.2 MF. Now that may not seem like much but even a small deviation can move the cross-over values and electrical response way off kilter. The BC1 has an exotic three way crossover - thus the need for six caps and four wound bobbins on each board.

Anyway, the bottom line is this. My BC1s sounded pretty good before and now they sound fantastic. I just got off the phone with the guy who installed the caps to thank him. They are smoother across the entire mid-range by a country mile and I can tell the cross-overs are spot on by the renewed voicing and tonal coloring. The resolution of low level detail is now even better than when they were new speakers.

I am not sure that the problems you are having are all cross-over related - but they could be, and a rebuild of the X-over on a quality older speaker system is highly recommended. It is also a good idea, where possible, to rotate the woofers 180 degrees to counteract speaker surround sag, which gravity induces and which often leads to scratchy voice coils.

Cheers,
David Neice


Forgot about that David. Thanks for bringing that up!

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PostPosted: Fri May 04, 2018 9:16 am 
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I agree when sonics seem off first place to look is the x/o caps. as others mentioned current prod caps are mainly inexpensive and of a tighter tol.

do poly or mylar dry up? theres no electrolytic, only a poly or if mylar a mylar film. that why they call em film caps and not electrolytic caps.

the given environment should not affect longevity of the component and as one mentioned his caps were still within 0.2uF of rating.
now on a 2.2, 4.7, 6.8 etc cap that more than likely had a +/- 10 or 20% tolerance we're still well within spec.
its the esr on that aging part that's the issue imo.

2nd place to look would be if any carbon resistors exist. these sometimes like to drift. yoink em and toss in a good wirewound.

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PostPosted: Fri May 04, 2018 11:22 am 
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Thanks for the responses guys. Last year I recapped my Celestion SL6s, and the difference was quite profound, similar to David's description regarding his BC1. The Celestions used Alcap electrolytics, and I replaced with the same blue caps from Falcon Acoustics. A few years back I had a pair of 1975 Klipsch Heresy, and thought I'd have the crossovers checked out. The tech said upon inspection that the caps were Mylar, so need at all so change them out. I happily took them home and enjoyed them. But as said, I'm sure that something is off with the DM5. Very flat, very limited top end and detail. I'll take them in for a checkup. I had a look at a crossover (very easy and accessible, as 4 screws hold a metal plate mounted right on the front baffle), and the arrangement consists of 6 rather large tan coloured rectangular caps with rounded edges. Probably quite common in the day I would think. I also had a look at one of tweeters (pretty substantial unit with a large magnet), and the date stamped indicated Nov 19, 1979. This pair must be among the last of the DM5 generation.


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PostPosted: Fri May 04, 2018 11:36 am 
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Conventional wisdom is that electrolytic capacitors degrade while film caps (poly, mylar, etc) do not. When I changed the factory film caps my 1975 Tannoy Berkeley crossovers with new entry level Clarity Caps the improvement was significant, so I think it's worth changing them no matter what the type. Changing caps on a speaker crossover is really easy in most cases, and the parts aren't expensive either.


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PostPosted: Fri May 04, 2018 11:41 am 
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electrafixion wrote:
Conventional wisdom is that electrolytic capacitors degrade while film caps (poly, mylar, etc) do not. When I changed the factory film caps my 1975 Tannoy Berkeley crossovers with new entry level Clarity Caps the improvement was significant, so I think it's worth changing them no matter what the type. Changing caps on a speaker crossover is really easy in most cases, and the parts aren't expensive either.


That just means you used *better* caps, not that the old one's were broken.

-- 04 May 2018 19:43 --

BinkyTheCat wrote:

2nd place to look would be if any carbon resistors exist. these sometimes like to drift. yoink em and toss in a good wirewound.


A wire wound will add inductance.

I'd replace with a fresh carbon or a metal film.


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PostPosted: Fri May 04, 2018 11:50 am 
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Inductance should be minimum because we're winding around an insulator not a ferrite core

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PostPosted: Fri May 04, 2018 12:00 pm 
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Here is the crossover board. I can see 3-3 100V stamped on the two outside caps and a 4-7 100V on one cap on the other side of the cluster. No resisters. The narrow black cylinder is a fuse casing.


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Last edited by cyrus on Sat May 05, 2018 2:44 am, edited 1 time in total.
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PostPosted: Fri May 04, 2018 12:09 pm 
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cyrus wrote:
Here is the crossover board. I can see 3-3 100V stamped on the two outside caps and a 4-7 100V on one cap on the other side of the cluster. No resisters. The narrow black cylinder is a fuse casing.

That capacitor form factor is also common on older Tannoy speakers You may run into problems trying to find audio specific caps that fit easily, but WIMA MKP4 or MKP10 would be good choices in that physical size.


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PostPosted: Fri May 04, 2018 12:15 pm 
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Nothing wrong with wima. I'd bypass the fuse too...but that's just me.

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PostPosted: Fri May 04, 2018 12:45 pm 
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David, were the original caps on your Spendor similar to the B&W as pictured?


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PostPosted: Fri May 04, 2018 1:11 pm 
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Stay away from Solen, bland sound, average at the best.
Tried them a few times in X-overs, not happy.
Have to admit I'm picky.


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PostPosted: Fri May 04, 2018 1:13 pm 
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BinkyTheCat wrote:
I agree when sonics seem off first place to look is the x/o caps. as others mentioned current prod caps are mainly inexpensive and of a tighter tol.

do poly or mylar dry up? theres no electrolytic, only a poly or if mylar a mylar film. that why they call em film caps and not electrolytic caps.

the given environment should not affect longevity of the component and as one mentioned his caps were still within 0.2uF of rating.
now on a 2.2, 4.7, 6.8 etc cap that more than likely had a +/- 10 or 20% tolerance we're still well within spec.
its the esr on that aging part that's the issue imo.

2nd place to look would be if any carbon resistors exist. these sometimes like to drift. yoink em and toss in a good wirewound.


I used the term dry up, but lets rephrase that to "go bad". They leak electricity. Ever had a power tube red plate? That's usually a film cap gone bad. Ever change out old film caps in speakers, amps, etc. and hear a difference because the bass and/or treble are no longer rolled off. That's a bad film cap. We've all read about someone having a pc of vintage gear and not liking the sound after being re-capped. The new film caps have revealed the true quality of the item because good stuff will sound better after a rebuild. One can check a cap for leakage at full voltage with a real cap tester such as the old Sprague TO series, but not a volt meter.

Carbon comp resistors drift as soon as they're made. Get rid of them. It's so rare that they're within spec it's not worth the time to check them ... unless you want to know how far they've drifted!

-- Fri May 04, 2018 4:17 pm --

deltaV wrote:
Stay away from Solen, bland sound, average at the best.
Tried them a few times in X-overs, not happy.
Have to admit I'm picky.


Don't tell Carl M:

http://www.nolaspeakers.com/index.php

Alon speakers use them but not sure about Nola. If Alon's get any better the sound stage will go around the globe! Lol

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