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 

My 107 restoration project - Help requested

 
Post new topic   Reply to topic    SpeakerTalk Forum Index -> KEF speakers
View previous topic :: View next topic  
Author Message
geoffwood
Intermediate Contributor 25+


Joined: 24 Sep 2009
Posts: 37
Location: Wellington, New Zealand

PostPosted: Tue Sep 29, 2009 4:02 am    Post subject: My 107 restoration project - Help requested Reply with quote

First , request list:
1 - KUBE 107 setup procedure
2 - KUBE 107 schematics
3 - R107 (Mk1) crossover schematics

KEF UK, and their NZ distributors appear to have no info other than for 107.2 ;-(

Recently picked up a pair in 'reasonable' nick, and a KUBE 107 (separately). And sold off my beloved R105.2 ;-(

First problem was that the KUBE 107 oscillated at several MHz. Cured that by popping 100nF caps between legs of the 3T regulators, and later found the 10uF capacitors to have miniscule actual values , and of course replaced those (and the other two) electrolytics. All good now.

But the speakers although having pants-wetting bass, sounded really quite shrill. I'd read that they would sound toppy without the KUBE, but this was extreme.

Next - better try setting up with the KUBE ? Given no redaily available instructions, I made up a CD with spot tones at 80 Hz, 1K5, and 5 K, plus sweeps from 20-200, 200-5K, and 2K-20K, and 20-20K, figuring the spot tones should be centre(ish) of the LF band (for reference) and the MF and HF bands so I could tweak the preset pots to even things up. (And what is that third pair of presets for - overall channel level ? )

But no, the adjustment was not sufficient to bring the MF/HF within 15dB of the (apparently low level) LF. Then I tried the lowest of my sweeps - a lot of flappy farting sounds at the extreme bottom end, then mostly good except for a sharp resonance at 100Hz. Time to pull the top off.

Looked down into the cavity and was somewhat surpised to be able to see the lower woofer as well as the upper - the foam surounds were essentially GONE ! But they still sounded pretty much OK on music apart from the imbalance ! Amazing.

Have got the woofers away for new surrounds (still waiting), and have replaced the T33s with the 'new' version for R107, R1549X. While waiiting I have rewired the internals with 2.0mm2 generic OFC cable (may or may not make a difference, but what the heck ?!!!). Might recap the x-over at some stage...

HOWEVER, I really do need the proper setup procedure for the KUBE 107, plus the schematics if possible. I may replace the TL071 opamps with something slightly higher-zoop. All caps appear to already to be MKPs.

I have the 107.2 crossover schematics, and the '107.1' does seems very similar, LF cab end, if not dalek-head end.

Grateful any info, and ancedotes.

cheers

geoff
Back to top
View user's profile Send private message
François
Junior Contributor 10+


Joined: 06 May 2009
Posts: 13
Location: Rennes, France

PostPosted: Sat Oct 17, 2009 11:21 am    Post subject: Reply with quote

No info I'm afraid, but an anecdote : reading your message, I didn't have to wait to you opening the top to know your woofers' foams were shot.... It's the major problem with the 107, today every 107 woofer is either shot or reconned. The other problem being the solidified ferrofluid tweeters if I remember well. Good to know when buying a pair.

You have the technical approach, but I'd say that when you'll receive your restored woofers, you'll don't need anything more than adjusting your kube to what your ears like Smile
Back to top
View user's profile Send private message Visit poster's website
speakerguru
Über Contributor 1000+


Joined: 18 Nov 2005
Posts: 1033
Location: Green Hut, Tovil

PostPosted: Sun Oct 18, 2009 8:36 pm    Post subject: Re: My 107 restoration project - Help requested Reply with quote

geoffwood wrote:
I may replace the TL071 opamps..........

The op amps will all be doubles i.e TL072, not TL071
Read my other KUBE posts before doing anything rash. e.g. you won't get lower noise just be changing op amps; you have to scale down the impedance of all associated components to reduce Johnson Noise.
Back to top
View user's profile Send private message
geoffwood
Intermediate Contributor 25+


Joined: 24 Sep 2009
Posts: 37
Location: Wellington, New Zealand

PostPosted: Tue Oct 20, 2009 9:19 am    Post subject: Thought ... Reply with quote

I had posted a reply (twice) but nothing has appeared.

Anyway, agaaaain:

Having just had my woofers refoamed, and re-installed them ( is it always a bit fraught ensure they are correctly polarised Wink ), and fire them up with my fixed KUBE 107 ( PSU caps), I am now happy that there is no great urgency to update the opamps - sounds like plenty of 'air' around the detail, and the new R1549X tweeter sounds far smoother and extended than the older T33 (R1210X) - must this may be psychological.

107s sound waaay better than before - much better balance with the bass. However I still cannot set them 'perfectly'. I made a CD with tones at 80Hz, 600Hz, and 5KHz, being central to the band of each driver. With the 'unadjustable' LF 80Hz with Contour at "0" as the reference, the best I can adjust the other drivers to with the KUBE internal preset pots are MF +2.5dB, and HF +5dB. These are measured with a suitable microphone. Must hook up to spectrum analysis in Sound Forge at some point.

And what are the third pair of presets in the KUBE - presumably something at the vLF end, as they make no measurable effect at my test frequencies.

With the Contour wound up full this brings the LF into line with the MF, but the HF is still noticably high. I would really like to know the proper setup procedure.

I have read AndrewJ's crossover explanation, and have the 'lower box' crossover schematic, but if I need to change some padding resistors in the HF dalek crossover, I still lack the schematic of that.

Does anybody know if www.diyaudio.com member AndrewJ (maybe = Dr Andrew Watson , KEF designer ???) is still around ? Have tried online messaging him but no luck...

geoff
Back to top
View user's profile Send private message
speakerguru
Über Contributor 1000+


Joined: 18 Nov 2005
Posts: 1033
Location: Green Hut, Tovil

PostPosted: Wed Oct 21, 2009 8:24 am    Post subject: Reply with quote

AndrewJ on the diyaudio forum is Andrew Jones. He did most of the work on the 107 Kube. He is still around but very busy and hard to get hold of. When I spoke to him earlier this year, he was still working for the pro speaker division of Pioneer in the Los Angeles area.

Re your Kube, could the unknown pots just be dc offset adjustment? We tried to keep to dc coupling throughout the Kubes wherever possible but the Friend biquad stages could sometimes have a lot of gain to the op-amp's internal dc offset, hence the occasional coupling capacitor or dc preset pot.
Back to top
View user's profile Send private message
geoffwood
Intermediate Contributor 25+


Joined: 24 Sep 2009
Posts: 37
Location: Wellington, New Zealand

PostPosted: Sun Nov 08, 2009 9:55 am    Post subject: Reply with quote

OK, yes. It turns out the 'front' presets are for offset. One channel was 36mV and the other 170mV, and I was able to tweak them to within a single millivolt.

AndrewJ did catch up with me ( thanks !) but has temporarily disappeared again - good to be busy.

I am still not able to tame the treble, which is 4dB high, so will try to trace the cct and figure out what to change to give a greater than 3dB range for the trimpots. Unless somebody can find a schematic of the older KUBE ( KUBE 107 , '3 knob').

geoff
Back to top
View user's profile Send private message
Parts
Senior Contributor 100+


Joined: 13 Jan 2006
Posts: 176
Location: Edinburgh

PostPosted: Sun Nov 08, 2009 10:15 pm    Post subject: Reply with quote

I have a schematic somewhere in the loft I believe, it is full size though so may be difficult to get onto the PC, I need to go up there within the next couple of days so will try and find it.
Back to top
View user's profile Send private message
geoffwood
Intermediate Contributor 25+


Joined: 24 Sep 2009
Posts: 37
Location: Wellington, New Zealand

PostPosted: Sun Nov 08, 2009 10:37 pm    Post subject: Reply with quote

That would be super. FWIW I can scan A3 directly to PDF for you, but I'm in New Zealand !

Also after schem of the 'top' crossover, but I guess I can more easily trace that for myself...

geoff
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