SpeakerTalk Forum Index SpeakerTalk
This forum has been set up to facilitate discussion of 1970s KEF speakers and drive units. The owner of the Forum has no connection with KEF Audio.
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

Capacitor size - KEF 105

 
Post new topic   Reply to topic    SpeakerTalk Forum Index -> KEF Speakers from the 1970s
View previous topic :: View next topic  
Author Message
lt2525
Intermediate Contributor 25+


Joined: 14 Oct 2009
Posts: 29
Location: Canada

PostPosted: Thu Dec 01, 2011 8:14 pm    Post subject: Capacitor size - KEF 105 Reply with quote

Hi,
I am just getting back to an earlier project to repair the x-over in a pair of KEF 105 -1's.

Some of the components had been damaged by an electrical accident Crying or Very sad

Anyway, I have now managed to obtained a replacement coil for the damaged coil and replacement capacitors for the damaged capacitors.

I also figured that since I had to replace some capacitors, it might be a good idea to update all the old capacitors at the same time. So I went ahead and ordered some caps from Solen (400v poly).

The problem I have run into is that some of the new caps are much larger than the old caps. For the most part, some rearranging has allowed things to fit. However the 100 uF cap is VERY much larger than its corresponding vintage unit (56 mm diameter X 72 mm L). If I mount this directly to the PCB there is no way I can get the back cover reattached.
Looking at the enclosure, I notice that there is a fair bit of open space at the top of the enclosure behind the tweeter. I was wondering about possibly mounting the 100 uF cap in that area and wiring it back to the PCB.

The question I have is would the presence of this rather large cylindical object in the open space behind the tweeter have any effect on the sound that the tweeter is putting out the front of the speaker?

Any comments appreciated.

Cheers
Back to top
View user's profile Send private message
ColinR
Über Contributor 1000+


Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Thu Dec 01, 2011 8:28 pm    Post subject: Reply with quote

Might be better to think along the lines of extending the wires from the drive units and an external crossover in a plastic lunch box.
_________________
This post or any other information supplied to this website or any other by myself is not available for any form of commercial purpose i.e. to hi-fi magazines or as sales and marketing material for sleezeBay or Audiodogging pimps and the like.
Back to top
View user's profile Send private message
lt2525
Intermediate Contributor 25+


Joined: 14 Oct 2009
Posts: 29
Location: Canada

PostPosted: Thu Dec 01, 2011 8:35 pm    Post subject: Reply with quote

So, you'd put the entire xover in an external box?
Back to top
View user's profile Send private message
ColinR
Über Contributor 1000+


Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Thu Dec 01, 2011 8:50 pm    Post subject: Reply with quote

Quote:
you'd put the entire xover in an external box


Yes, hanging all the bits of the PCB is preferable to extending the wires on individual components.

There is an electronics mantra with Zenner diodes and resistors "keep the leads as short as possible" so in a passive crossover it's probably best to have all the action taking place for an individual drive unit as per original design.
_________________
This post or any other information supplied to this website or any other by myself is not available for any form of commercial purpose i.e. to hi-fi magazines or as sales and marketing material for sleezeBay or Audiodogging pimps and the like.
Back to top
View user's profile Send private message
lt2525
Intermediate Contributor 25+


Joined: 14 Oct 2009
Posts: 29
Location: Canada

PostPosted: Thu Dec 01, 2011 8:57 pm    Post subject: Reply with quote

Idea OK, thanks for the feedback. I'll look into the lunchbox.


On a side note and basically for my own interest, could you comment on the original question?.... would having a largish object in the open space behind the tweeter influence the sound coming out of the front?
Back to top
View user's profile Send private message
ColinR
Über Contributor 1000+


Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Thu Dec 01, 2011 9:04 pm    Post subject: Reply with quote

Quote:
could you comment on the original question?.... would having a largish object in the open space behind the tweeter influence the sound coming out of the front?


No as the T52 has a sealed back.

With an open-backed design without damping material the omnidirectional polar plot would morf into something strange due to reflection and refraction off the cylindrical component.
_________________
This post or any other information supplied to this website or any other by myself is not available for any form of commercial purpose i.e. to hi-fi magazines or as sales and marketing material for sleezeBay or Audiodogging pimps and the like.
Back to top
View user's profile Send private message
audiolabtower
VIP Contributor 500+


Joined: 06 Jan 2009
Posts: 544

PostPosted: Thu Dec 01, 2011 10:35 pm    Post subject: Reply with quote

According to Martin Colloms and others external passive crossovers have multiple advantages. Many years ago I measured all the caps in my 105s and replaced them with polyprops and polyesters to better than 0.25%. At the same time the crossovers were taken out and put in plastic cases near to the amp terminals and tri-wired back to the drive units. This was necessary because the series bass 360uF was made up of 12 large 30uF caps plus padding so would have had to have been hot melted together in a huge "blob" to be put inside the cab. But according to the articles of the time the cable run on the output side of the crossover to drive unit is a lot more forgiving then a long cable run on the input side of the crossover.
Back to top
View user's profile Send private message
Innercity126
Intermediate Contributor 25+


Joined: 25 Oct 2011
Posts: 39
Location: Sea World, Texas

PostPosted: Sat Dec 03, 2011 5:28 am    Post subject: Reply with quote

IT2525,

I am doing the same thing to my 105's, except in reverse. The previous owner had already modded the crossovers, using poly caps, and the 100uf cap was huge. He used long lead wires to the board, and mounted the cap, using hot glue, to the top of the inner tweeter cavity. The glue did not hold, and the cap was left just dangling inside.

Were I to have done this, I would have pre-mounted the (100uf) cap to a small piece of board using nylon tie straps and mounting blocks (like the ones found at Bob Crites Speakers), and then screw the board to the top of the inner cavity, making it a much more secure fixture.

However, since I am fully restoring the speakers now, I decided to return the crossovers back to their original state and am using Alcap electrolytic caps, purchased from Falcon Acoustics, so everything fits back on the board like the OEM ELcaps.

Anyway, just thought I'd chime in. Have fun with the upgrade.
Back to top
View user's profile Send private message
ColinR
Über Contributor 1000+


Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Sat Dec 03, 2011 10:36 am    Post subject: Reply with quote

"Baked bean tin sized" components and their cost, having to fiddle with resistors to get the ESR and ESL closer to those of the old electrolytic capacitors makes me think going active might be a more attractive proposition.
_________________
This post or any other information supplied to this website or any other by myself is not available for any form of commercial purpose i.e. to hi-fi magazines or as sales and marketing material for sleezeBay or Audiodogging pimps and the like.
Back to top
View user's profile Send private message
lt2525
Intermediate Contributor 25+


Joined: 14 Oct 2009
Posts: 29
Location: Canada

PostPosted: Fri Dec 09, 2011 5:26 pm    Post subject: Reply with quote

Well just to update, I looked at creating an outboard lunch box but decided against it.
Given the wiring necessary from both the input to the output and the necessity of having this box sit somewhere close to the speakers made me a bit hesitant. The final straw was that I was unable to find a suitable box at my usual supply source.
So I just decided to try the other route. If it sounds bad, I can always change it around.

For the physical mounting, I used an old hard coaster (cork based) that I had hanging around. This coaster fit exactly into the existing cavity at the top of the enclosure. I drilled several holes and applied a generous dollop of Plumber Goop to the coaster board. I sat the cap into the Goop and used tye-wraps around the cap and through the holes I had drilled to keep it all secure. The coaster slid right in on top of the horizontal support struts on the interior of the enclosure. Some more Goop on the struts secured the coaster board to it.

I ran about a 3 inch lead back to the PC Board to complete the electrical connection. Given that this is a connection for a 100 mF cap, my thinking was that while the additional leads are undesirable, the large cap value in this leg of the circuit would more than compensate for any slight variations introduced by the added leads.

Anyway, I then put everything back together.

Side note* as I removed each of the old caps I measured them with my hand held meter. The values varied quite a bit from the nominal values, 20% or more. The new caps I put in were also measured and accurate to within less than 1 %.
After repairing the one speaker, I decided that instead of also replacing the caps in the undamaged companion speaker that it might be fun to leave it alone and do some A-B comparisons between both.

So I installed both enclosures back onto the woofer cabinets. Funnily enough while moving the cabinets from the work area back to the listening area they got mixed around and by the time I had them set up with a music source, I could not really tell which was which. All the better for A-B comparisons!

I have now tried a variety of source material and my first comment is OMG, I forgot how great these speakers sounded!

Secondly, to my ears there is no discernible difference between Left and Right so far. That is, of course, curious given the capacitor readings on the original caps and the changes I made.

I plan to continue my listening tests. I remember reading somewhere that some people say it takes some time for new caps to "burn in" .

However unless I can hear a difference, I don't know if it's worthwhile recapping the second speaker.
Back to top
View user's profile Send private message
audiolabtower
VIP Contributor 500+


Joined: 06 Jan 2009
Posts: 544

PostPosted: Fri Dec 09, 2011 7:19 pm    Post subject: Reply with quote

The 20% could be age drift by now if they are original components. However when built the caps might not be anywhere near exact values because they were all selected into 1% bands and then matched to the drivers and inductors by the computer to centre the result of the whole.

Looking back at my notes when my caps were still relatively new for example one 3.3uF in the tweeter feed was 3.87uF and 3.81uF selected deliberately around 16% high. Similarly the other 3.3 was 3.55 and 3.52uF.
Back to top
View user's profile Send private message
lt2525
Intermediate Contributor 25+


Joined: 14 Oct 2009
Posts: 29
Location: Canada

PostPosted: Fri Dec 09, 2011 7:34 pm    Post subject: Reply with quote

Hmmmm, that's curious. So if I understand properly you are saying that the circuit was built around the actual value of the cap as measured at the time, rather than the nominal value of the units?

I was thinking that this might be due instead to my measuring tool.
I received the following insert from Falcon Acoustics:

"....Please note that most handheld multimeters do not use the correct test frequency for capacitors, particularly electrolytics, and therefore give unreliable results....."

I am using an inexpensive handheld. It does however measure the poly's right on.
Back to top
View user's profile Send private message
audiolabtower
VIP Contributor 500+


Joined: 06 Jan 2009
Posts: 544

PostPosted: Fri Dec 09, 2011 9:16 pm    Post subject: Reply with quote

Yes, caps were bought in at 10 or 20% tolerance, and sorted into 1% bands by hand, the inductors were then wound to suit so if a cap was +5% the corresponding inductor was made -5% approx.

I was lucky in that I worked in a lab with a professional LC bridge at the time where you could plot against frequency, but I guess a handheld is better than nothing at all.
Back to top
View user's profile Send private message
speakerguru
VIP Contributor 750+


Joined: 18 Nov 2005
Posts: 954
Location: Green Hut, Tovil

PostPosted: Fri Dec 09, 2011 10:44 pm    Post subject: Reply with quote

audiolabtower wrote:
Yes, caps were bought in at 10 or 20% tolerance, and sorted into 1% bands by hand, the inductors were then wound to suit so if a cap was +5% the corresponding inductor was made -5% approx.


Absolutely correct. I used to hate having to make up the component matching chart which went on the crossover drawing, which in turn told production what values of inductors to wind depending on what stock of capacitors they had.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    SpeakerTalk Forum Index -> KEF Speakers from the 1970s All times are GMT + 1 Hour
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group