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 103.2 Crossover upgrade
Goto page 1, 2, 3, 4  Next
 
Post new topic   Reply to topic    SpeakerTalk Forum Index -> KEF speakers
View previous topic :: View next topic  
Author Message
fried226
Introductory Contributor


Joined: 23 Apr 2008
Posts: 3

PostPosted: Fri Apr 25, 2008 5:25 am    Post subject: KEF 103.2 Crossover upgrade Reply with quote

First, thanks for this great forum. I really appreciate the information here.
I love the classic warm, musical mid-range and lower mid-range from my KEF 103.2 I'm less enamored by what I perceive as harshness and heaviness in the upper frequencies. I know the tweeter was never sweet or airy and has been described as "spitty". I'm looking for a sort of holy grail of speaker with the high frequencies of my NHT superzero and the midrange and mid-bass of the 103.2
To first bring the 103.2 at lease up to spec, I thought I'd start by replacing some of the capacitors on the crossover. I'd like to do this cost-effectively. To that end, I have some questions:
By the way, please forgive my ignorance about loudspeaker design. For instance, I see that there are 2x 300mfd caps in the B200 circuit. Are these hi-cuts for the woofer? I'm seeing various other caps of differing values. Do the smaller values represent more treble-critical caps? Would it make sense to purchase more expensive (read: musical, transparent) caps for the smaller values (2.2, 4.2 mfd) and more common ones for other, larger capacitors? I've read that it's almost always preferable to replace these electrolytic caps with polymer types. Is that a correct assumption given the characteristics of the T33 unit? Also, I've read about replacements for the T33, but these were all recommended in the context of usage in the 104.2 system. Do these recommendations stand for the 103.2 system as well? Thanks for the information in advance and as I update these speakers I'll continue to keep you updated as to any of the benefits of this endeavor.

-Mike
Back to top
View user's profile Send private message
speakerguru
VIP Contributor 750+


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

PostPosted: Fri Apr 25, 2008 11:39 am    Post subject: Reply with quote

The 600uF in series with the woofer is essential for the correct operation of the protection circuit, but it also extends the low frequency response by its interaction with the inductance in the woofer equivalent circuit, due to the driver/box suspension. The cut-off frequency is reduced below the box resonance and the roll-off below cut-off is increased from the 12dB/oct of the closed box to 18db/oct, which is still less than a reflex design.

There is an equivalent effect above resonance as the series inductance of the woofer crossover becomes large. The crossover inductor interacts with the capacitance due to the mass of the moving parts, which produces a peak in the response, with a corresponding drop in impedance, in the region above resonance. The only way to avoid this it to have impedance compensation networks across the woofer to make it look resistive.

By all means change the tweeter capacitors to non-electrolytic types. They are more reliable. However you will be losing up to 1 Ohm of equivalent series resistance, which had all been factored into the original design, so you should either put in extra series resistors or you'll have to live with a small but significant increase in tweeter level.
Back to top
View user's profile Send private message
fried226
Introductory Contributor


Joined: 23 Apr 2008
Posts: 3

PostPosted: Mon Apr 28, 2008 2:42 pm    Post subject: Reply with quote

Thanks speakerguru. I appreciate the insights. I'm wondering that perhaps assertions of polypro capacitors making speaker systems sound more transparent and airy are merely the by-product of higher tweeter output level due to loss of ESR. I probably will use polypro caps to replace at least some of these lytics because I believe that the T33 has incurred some loss of sensitivity and/or output power due to loss age vis-a-vis ferrofluid evaporation. Scientifically, how can I measure these tweeters to check that they are indeed outputting to spec? Also, is is true that the smaller value caps are more responsible for tweeter behavior? By the way, can anyone chime in for potential T33 replacements in the 103.2?
Back to top
View user's profile Send private message
ColinR
Über Contributor 1000+


Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Mon Apr 28, 2008 9:25 pm    Post subject: Reply with quote

The Ref 103-2 uses a B200G and a T33A SP1074; it being a conventional soft dome design does not use a ferrofluid coolant.

Although I did see some 103-2s retofitted once with 4 Ohm mk2 T33 units on a Manchester based studio equipment disposal website.

KX9
_________________
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
speakerguru
VIP Contributor 750+


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

PostPosted: Tue Apr 29, 2008 8:21 am    Post subject: Reply with quote

fried226 wrote:
Scientifically, how can I measure these tweeters to check that they are indeed outputting to spec?
Short answer; you can't, unless you have a quiet, reflection-free site for acoustic measurements and a calibrated microphone.
fried226 wrote:
Also, is is true that the smaller value caps are more responsible for tweeter behavior?
Not sure what you mean by this. Only the capacitors in the tweeter section of the crossover filter will affect the tweeter output. As the tweeter works at higher frequencies than the woofer, then the capacitors in the tweeter part will be smaller than those in the woofer section. Xc = 1/(2*pi*f*C) i.e. at high frequencies you need a smaller capacitor for a given impedance than you do at low frequencies.
Back to top
View user's profile Send private message
O'Shag
Intermediate Contributor 50+


Joined: 28 Feb 2008
Posts: 69
Location: City of The Angels

PostPosted: Tue Apr 29, 2008 9:39 pm    Post subject: Reply with quote

speakerguru wrote:
The 600uF in series with the woofer is essential for the correct operation of the protection circuit, but it also extends the low frequency response by its interaction with the inductance in the woofer equivalent circuit, due to the driver/box suspension. The cut-off frequency is reduced below the box resonance and the roll-off below cut-off is increased from the 12dB/oct of the closed box to 18db/oct, which is still less than a reflex design.

There is an equivalent effect above resonance as the series inductance of the woofer crossover becomes large. The crossover inductor interacts with the capacitance due to the mass of the moving parts, which produces a peak in the response, with a corresponding drop in impedance, in the region above resonance. The only way to avoid this it to have impedance compensation networks across the woofer to make it look resistive.

By all means change the tweeter capacitors to non-electrolytic types. They are more reliable. However you will be losing up to 1 Ohm of equivalent series resistance, which had all been factored into the original design, so you should either put in extra series resistors or you'll have to live with a small but significant increase in tweeter level.


Wow mate - terrific information! The moniker is indeed well-deserved! If you ever open a speaker builder's 'Ashram', count me in as a member. Smile On a related question; what are your thoughts on teflon capacitors? I've heard it said that they are a 'breakthrough' in audio. I have no experience myself, b ut I was wondering what are your thoughts on teflon caps from an engineering perspective?
Back to top
View user's profile Send private message Send e-mail
fried226
Introductory Contributor


Joined: 23 Apr 2008
Posts: 3

PostPosted: Thu May 22, 2008 7:52 am    Post subject: Reply with quote

I replaced all the tweeter circuit capacitors (except for the 2x10 uf: cant find non-polar with 100v...anyone know where I can?) in this crossover yesterday. After considering the freq response drift that would occur with lower ESR polymer capacitors (thanks speakerguru), I decided to stay with 'lytics. However, I did "bypass" these capacitors with "high quality" .01uf film/foil types. I did one speaker system at a time and listening to the updated and original at the same time in the extreme nearfield I detected similar freq responses, but a more airy, less congested upper mid- to high freq in the updated speaker system. Definite improvement in this regard, and really took care of the initial problem that I had with the KEF's. The actual high freq response was always adequate (although slightly shy of today's (shrill?) standard's) but there was always to my ears a congestion there. Anyone who has similar greivances with the vintage KEF speaker systems might be pleased with this modification. BTW, since high freq response did not change much, I concluded that even though these speakers are 25+ years old, capacitor leakage had minimal effect on freq response.
Back to top
View user's profile Send private message
speakerguru
VIP Contributor 750+


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

PostPosted: Thu May 22, 2008 11:25 am    Post subject: Reply with quote

O''blocked word' wrote:
On a related question; what are your thoughts on teflon capacitors?

Never used them or come across them. Tried a Google search to find advantages/disadvantages of Teflon and have so far come up with nothing.
My RF engineer colleague tells me that Teflon is a form of PTFE, which is a very low loss dielectric and is used in high spec RF connectors, but niether of us can see any significant advantage over polypropylene at audio frequencies.
Back to top
View user's profile Send private message
tancrède
Intermediate Contributor 25+


Joined: 12 May 2004
Posts: 34
Location: Quebec Canada

PostPosted: Fri Jun 13, 2008 12:05 am    Post subject: new old 103.2 from Tancrède Reply with quote

------------
Hi

I just bought 103.2 and sound great

but i measure the OHM output on the rear connector, with Fluke 83, and it's around 4 mega.

Isn't suppose to be arouns 8 ohms even with the protection circuit ?????
So caps must be Kapout or so...

Caps on the Crossover are ALLCAP(in metal case) and they seem to be electrolytics

I try to pull-it off of the boxe, after i took-off the nut, but the glue is incredibelbly strong

Sorry folks, i usually write in french Québecois

Thanks

Tancrède
Back to top
View user's profile Send private message Send e-mail
tancrède
Intermediate Contributor 25+


Joined: 12 May 2004
Posts: 34
Location: Quebec Canada

PostPosted: Fri Jun 13, 2008 12:15 am    Post subject: Reply with quote

----------
I forgot

They dont have much treeble. Is that confirm that Caps Crossover are in troubles ?????

Tancrède
Back to top
View user's profile Send private message Send e-mail
tancrède
Intermediate Contributor 25+


Joined: 12 May 2004
Posts: 34
Location: Quebec Canada

PostPosted: Fri Jun 13, 2008 6:21 am    Post subject: Reply with quote

Wow

This site show exactly my Crossover

Caps are electrolytics non-polarized.

http://www.hifiloudspeakers.info/Anatomy/SpeakerSystems/103.2/ColinRoyle/KEF103.2XOver.jpg


And this one is the schematical without the protection circuit

http://www.hifiloudspeakers.info/Anatomy/Crossovers/103.2/SP1144103.2CrossoverIndex.html
Back to top
View user's profile Send private message Send e-mail
tancrède
Intermediate Contributor 25+


Joined: 12 May 2004
Posts: 34
Location: Quebec Canada

PostPosted: Fri Jun 13, 2008 6:50 am    Post subject: suite Reply with quote

------------
Further more, my investigation try to show me that Crossovers is normal.

Because i discharge-it by the connector rear boxe, and with the multimeter, in measurement in OHM, the crossover caps charge and the ohms start at 1 ohms to 4 mega

The other speaker(boxe) do the same thing. So Crossover of the 2 speakers react exactly the same.

Only a very very big hazard can do this. If so, i sould take a ticket of lotery right now.

Well, i dont know how my AMP Audiolab can see a usual 8 ohms at his input for amplification ?????

Tancrède
Back to top
View user's profile Send private message Send e-mail
speakerguru
VIP Contributor 750+


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

PostPosted: Fri Jun 13, 2008 10:31 am    Post subject: Re: suite Reply with quote

tancrède wrote:
Well, i dont know how my AMP Audiolab can see a usual 8 ohms at his input for amplification ?????


8 Ohms is the "nominal" a.c. impedance across the audio band, 20 Hz to 20 kHz. You cannot measure this with a multimeter. A multimeter will measure d.c. resistance. With series capacitors the d.c resistance will only measure the leakage of the capacitors. You do not hear d.c. Laughing and I hope your amplifier is not producing d.c. Laughing
Back to top
View user's profile Send private message
proffski
Über Contributor 1000+


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

PostPosted: Fri Jun 13, 2008 6:06 pm    Post subject: Re: suite Reply with quote

Reminds of when I worked at Maplin, on more than one occasion a customer bringing back RG58 because it did not measure 50Ω on his pride and joy, a £10 multimeter...
Then trying to explain the difference between Resistance, Impedance, a lost cause...
One insisted that he was an engineer, ok! Wink

The term Foxtrot Whiskey was then the in-store description for them. Smile

Sorry to go off subject. Embarassed
_________________
I contend that for a nation to try to tax itself into prosperity is like a
man standing in a bucket and trying to lift himself up by the handle.
-Winston Churchill
Back to top
View user's profile Send private message Send e-mail
tancrède
Intermediate Contributor 25+


Joined: 12 May 2004
Posts: 34
Location: Quebec Canada

PostPosted: Fri Jun 13, 2008 7:03 pm    Post subject: Reply with quote

---------
I knew already all that folks

But usually, all speakers with Crossover have around 8 ohms.

8 ohms because od the pure resistance of the coil of the drivers and the coils of the Crossover. Capacitor with ohmmeter will charge the caps until the ready will be infinite in ohm.

Nevertheless, all speakers with Crossover have around 8 ohms

But 103.2 have a protection circuit. So the crossover is more complex.

Anyway, the thing is the those crossovers have around 4 megs resistance, and not 8

Dont forget that those speakers was made in 1983. Caps must be alterated

Tancrède
Back to top
View user's profile Send private message Send e-mail
Display posts from previous:   
Post new topic   Reply to topic    SpeakerTalk Forum Index -> KEF speakers All times are GMT + 1 Hour
Goto page 1, 2, 3, 4  Next
Page 1 of 4

 
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