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 

KEF crossover stuff for nerds,geeks and anoraks

 
Post new topic   Reply to topic    SpeakerTalk Forum Index -> KEF speakers
View previous topic :: View next topic  
Author Message
speakerguru
VIP Contributor 750+


Joined: 18 Nov 2005
Posts: 959
Location: Green Hut, Tovil

PostPosted: Tue Apr 11, 2006 12:14 pm    Post subject: KEF crossover stuff for nerds,geeks and anoraks Reply with quote

If you are rebuilding, repairing or replacing crossover components in KEF speakers of the 70s,80s and 90s, please note that the capacitors in all KEF crossovers were measured and sorted into 1% bands and inductors wound to suit. Capacitors values are not just what is marked on the outside of the casing.

This is particulary important in tweeter T sections where you could have two 3.3 or 5 uFs in series but in fact the one on the tweeter side is larger than the one on the amplifier side. If you get this the wrong way round you will get the wrong response and a lower impedance.

In general, as a sort of rule of thumb, around the cut off point of a crossover filter section, a 1dB change in frequency response will give a corredsponding 2dB change in impedance. So, if you have the larger cap at the input and the smaller cap at the tweeter, worst case, you could end up with a 1dB boost and a 2dB drop in impedance in the 2.5 to 3kHz region. Your amplifier may not like this. It may produce funny noises, as it current limits.


Last edited by speakerguru on Fri Nov 14, 2014 9:21 am; edited 1 time in total
Back to top
View user's profile Send private message
proffski
Über Contributor 1000+


Joined: 22 Aug 2003
Posts: 1297
Location: Tewkesbury UK

PostPosted: Wed May 17, 2006 12:24 am    Post subject: Re: KEF crossover stuff for nerds,geeks and anoraks Reply with quote

Use a Krell!
Back to top
View user's profile Send private message Send e-mail
iso
Senior Contributor 200+


Joined: 29 Aug 2011
Posts: 215
Location: Finland

PostPosted: Wed Nov 19, 2014 3:12 pm    Post subject: Reply with quote

This practice was economical way to build close tolerance crossovers... but not too cost effective for customer living in place like Finland. Only proper way to replace one failed capacitor was to by new crossover?

Were speakers of this time line never intended to be rebuilt properly? It seems odd that buyer received no information about actual values of crossover components used, as this information was available when actual crossovers were assembled.

Best Regards

Kimmo
Back to top
View user's profile Send private message
audiolabtower
VIP Contributor 500+


Joined: 06 Jan 2009
Posts: 544

PostPosted: Wed Nov 19, 2014 8:43 pm    Post subject: Reply with quote

Kef kept computer records for all the reference series selection of drivers/components with the exact values so if a failure occurred, a selected component could be sent to the service agent to restore exact original specification. Unfortunately when they went bust the records were thrown away when taken over by the Hong Kong company?
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 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