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 105 vs 105/2
Goto page Previous  1, 2, 3  Next
 
Post new topic   Reply to topic    SpeakerTalk Forum Index -> KEF Speakers from the 1970s
View previous topic :: View next topic  
Author Message
T.O. Chef
Senior Contributor 100+


Joined: 31 Aug 2007
Posts: 179
Location: Toronto Canada

PostPosted: Thu Nov 01, 2018 11:02 pm    Post subject: Reply with quote

I'd love to see that schematic AudioLT. Was it intended to be attached?

I guess then my questions are:
How crucial is the value of that cap. In my case a 30uF.
And, can I assume that inductor to be that value?, I was only assuming it based on all other 105 schematics.
Perhaps it's different in this configuration? I will attempt measuring it again. First time I tried my DATS program was unable to manage a value so low, but I can try once more, using a hand held device.

I find it fascinating that this (Tank ??) circuit + an aB should both be present in my 105's. The T-52's are the original versions, with the squared off face-plates. But the rear head coverings and the horizontal pcb position leads me to believe they are later versions. The build date is Nov. 1979.
I have re scanned the B-110b's and it seems the first time around I got a wonky L reading. Confirmed now: Both drivers are so close to published spec's is uncanny. Amazing indeed after all these years!
_________________
Music is food for the soul.
Back to top
View user's profile Send private message Send e-mail
audiolabtower
VIP Contributor 500+


Joined: 06 Jan 2009
Posts: 590

PostPosted: Thu Nov 01, 2018 11:10 pm    Post subject: Reply with quote

https://photos.app.goo.gl/fFrCCrYasywoT8pu6

Last edited by audiolabtower on Fri Nov 02, 2018 12:16 am; edited 1 time in total
Back to top
View user's profile Send private message
T.O. Chef
Senior Contributor 100+


Joined: 31 Aug 2007
Posts: 179
Location: Toronto Canada

PostPosted: Fri Nov 02, 2018 12:16 am    Post subject: Reply with quote

Alas ... no Google account here.
Reasons abound, but I won't get into them. Suffice to say, After 2 years I was finally able to escape from their grasp.

Oh how I wish we could all just do this within the forum. Post schematics and pictures easily.
I do understand the bandwidth issue though.

I'll PM an email.
_________________
Music is food for the soul.
Back to top
View user's profile Send private message Send e-mail
audiolabtower
VIP Contributor 500+


Joined: 06 Jan 2009
Posts: 590

PostPosted: Fri Nov 02, 2018 12:17 am    Post subject: Reply with quote

edited, try again.
Back to top
View user's profile Send private message
T.O. Chef
Senior Contributor 100+


Joined: 31 Aug 2007
Posts: 179
Location: Toronto Canada

PostPosted: Fri Nov 02, 2018 12:51 am    Post subject: Reply with quote

I see a huge series cap set on the HF input of that 105/2 layout as published by Colin. Not a parallel one.

I've been up and down all 105 crossover configurations, and actually have a set of 105/2 boards.

Maybe I'm blinded by age, but I don't see a parallel C/L on the HF input.
_________________
Music is food for the soul.
Back to top
View user's profile Send private message Send e-mail
audiolabtower
VIP Contributor 500+


Joined: 06 Jan 2009
Posts: 590

PostPosted: Fri Nov 02, 2018 2:52 pm    Post subject: Reply with quote

The 30uF is in parallel with the 0.028uF, thus both in series with the tweeter input. Can you see the link yet?
Back to top
View user's profile Send private message
T.O. Chef
Senior Contributor 100+


Joined: 31 Aug 2007
Posts: 179
Location: Toronto Canada

PostPosted: Fri Nov 02, 2018 3:54 pm    Post subject: Reply with quote

AH!!! Thank you Audiolabtower.
So there it is. my filter exactly (minus the aB) and it was the Mark ! version sporting it.
This is wonderful information, I'm so glad to know my crossover is not some anomaly or worse a 3rd party modification.

Now. I wonder what purpose it serves? Note I do have the early version t-52.
I have removed this 30uF cap. At this point I'm relatively pleased with the HF, though I do hear some ringing on classical piano works. Related perhaps to this circuit?

I'll reinstall the component and listen well to what my ears have to say about it, then report further.

Very Happy
_________________
Music is food for the soul.
Back to top
View user's profile Send private message Send e-mail
audiolabtower
VIP Contributor 500+


Joined: 06 Jan 2009
Posts: 590

PostPosted: Fri Nov 02, 2018 6:23 pm    Post subject: Reply with quote

C9 and C11 are open circuit on my board, but obviously there for the aB network if required.
Back to top
View user's profile Send private message
T.O. Chef
Senior Contributor 100+


Joined: 31 Aug 2007
Posts: 179
Location: Toronto Canada

PostPosted: Fri Nov 02, 2018 9:47 pm    Post subject: Reply with quote

Guru, thank you very much for that link explaining and calculating Tank Circuits. That has helped immensely analyzing a big issue.

I first reinstalled the aB circuit. Both sides test audibly very close to each other. Much of the tweeter ringing was reduced. To my ears they sound great!
Next, I put the tank circuit cap back in, one at a time. When both done there is a distinct mismatch in tonality side to side.

It must be the values used, they don't match the originals. And I can see from the calculator that a small change in value moves the resonance frequency quite a bit.

So, back to drawing board as they say. I'll remove that 30uF cap and find a way to get a perfect match, though I'm shooting in the dark a bit. At least I know if I can't get that circuit to behave as intended I can always just leave it out totally without much pain.
_________________
Music is food for the soul.
Back to top
View user's profile Send private message Send e-mail
speakerguru
Über Contributor 1000+


Joined: 18 Nov 2005
Posts: 1011
Location: Green Hut, Tovil

PostPosted: Fri Nov 02, 2018 11:20 pm    Post subject: Reply with quote

audiolabtower wrote:
https://photos.app.goo.gl/fFrCCrYasywoT8pu6

This circuit has been either wrongly traced or wrongly drawn. There is no way any KEF tweeter crossovers would have had a 5.5kHz trap in the input to the tweeter part of the crossover.

It's possible the input for the hf section was taken after the 30uF capacitor in the MF circuit. That could work, as 30uF is pretty much a short circuit at tweeter frequencies, but I can't think why it would have been done. It's far more likely someone has traced the circuit and made a mistake.

A straight series inductor of 28uH has an impedance of ~3.5 Ohms at 20kHz http://www.learningaboutelectronics.com/Articles/Inductor-impedance-calculator.php#answer
and I do recall that being used for some batches of tweeters with a rising response before cutoff. So a 0.028mH L may be correct in some instances, but never in parallel with any capacitor.
Back to top
View user's profile Send private message
T.O. Chef
Senior Contributor 100+


Joined: 31 Aug 2007
Posts: 179
Location: Toronto Canada

PostPosted: Sat Nov 03, 2018 1:05 am    Post subject: Reply with quote

speakerguru wrote:
It's possible the input for the hf section was taken after the 30uF capacitor in the MF circuit. That could work, as 30uF is pretty much a short circuit at tweeter frequencies, but I can't think why it would have been done.

My filter plainly has a dedicated 30uF in the MF section (input after the 1.3mH inductor).
This second 30uF cap is plainly inserted as described, in parallel with the .028mH inductor. I've been over the board 1000 times to confirm this.
It seems very odd though in that there's an anchoring nut & bolt that is very much in the way of the cap. It ends up quite squished between said nut and the cabinet sidewall.

Interestingly, the effect of this circuit is not at all noticeable to my ears On One Side, but it it has plainly a negative effect on side 2.

I confirm without hesitation that the circuit exists. It seemed to me that the filter was completely original component wise, there were no obvious tell tale signs of solder work.
That said, the etching of the SP1100 board in one spot shrieks of modification, as does the seemingly amateurish jumper wire from input to HF section (right after the Tank Circuit). I have not seen any KEF crossover built this sloppily.

Thank God it sounds good with the "Tank" emptied Smile
_________________
Music is food for the soul.
Back to top
View user's profile Send private message Send e-mail
T.O. Chef
Senior Contributor 100+


Joined: 31 Aug 2007
Posts: 179
Location: Toronto Canada

PostPosted: Sat Nov 03, 2018 1:10 am    Post subject: Reply with quote

MAYBE .... someone saw that crossover configuration on-line somewhere and decided this filter was incorrectly made? Then added the 30uF to match?
That seems feasible.
It doesn't explain the etched trace or the jumper wire to the HF section though.
_________________
Music is food for the soul.
Back to top
View user's profile Send private message Send e-mail
speakerguru
Über Contributor 1000+


Joined: 18 Nov 2005
Posts: 1011
Location: Green Hut, Tovil

PostPosted: Sat Nov 03, 2018 12:11 pm    Post subject: Reply with quote

T.O. Chef wrote:
That said, the etching of the SP1100 board in one spot shrieks of modification, as does the seemingly amateurish jumper wire from input to HF section (right after the Tank Circuit). I have not seen any KEF crossover built this sloppily.

Indeed. A modification by a previous owner is the most likely reason. No KEF tweeter ever needed an eq correction requiring a 5.5kHz notch. Period.
Back to top
View user's profile Send private message
T.O. Chef
Senior Contributor 100+


Joined: 31 Aug 2007
Posts: 179
Location: Toronto Canada

PostPosted: Sat Nov 03, 2018 2:13 pm    Post subject: Reply with quote

A few pictures here showing the filters "as found".

Note the etched trace on the left side. I have not attempted to decipher that revision, but everything seems to function as it should, aside from what's been discussed above.

https://nofile.io/f/3VCbrxsq8XA

https://nofile.io/f/fFaWtrTZS7e

Hopefully it can be confirmed the existence of the Parallel L/C on the top as shown.
_________________
Music is food for the soul.
Back to top
View user's profile Send private message Send e-mail
audiolabtower
VIP Contributor 500+


Joined: 06 Jan 2009
Posts: 590

PostPosted: Sat Nov 03, 2018 2:30 pm    Post subject: Reply with quote

I assumed the 30uF was part of the aB circuit, only used with the 0.22uF and 3.3/7uF combination. There are certainly designed spaces for these components on the pcb at C9 and C11 (0.22), unpopulated on mine, but no modifications in evidence.

If you look at the 104aB crossover it has an extra 10uF in the same series position but on the tweeter side, the only difference it is in parallel with a resistor instead of the 105 inductor. So maybe the total system design is not so much of an effect at 5.5kHz as the simple 30uF/28uH would imply in isolation?

Interestingly the voltage curve for the unofficial active 105 crossover shows the -6dB point at just over 3kHz, and a slight shaping at 5kHz of a dB or so - if we assume this was made to exactly mirror the original passive response?
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
Goto page Previous  1, 2, 3  Next
Page 2 of 3

 
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