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Recapping Best Practice? 103.2

 
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flextone
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Joined: 01 Mar 2015
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Location: Berlin, Germany

PostPosted: Sun Mar 01, 2015 9:15 pm    Post subject: Recapping Best Practice? 103.2 Reply with quote

First post, fantastic forum!

I know that recapping questions are very common and I did search the forum for answers. some questions have indeed been answered but others not exactly. As I read all over - on this and other forums as well as in the recapping sticky - recapping vintage KEF speakers is not straight forward. Values may differ from what is written on the capacitor etc. My question is basically, what's the best way to go about this? I was about to order Alcap capacitors from Falcon Acoustics when I realized I might be doing more harm than good. My 103.2 are currently used as studio monitors and I need the frequency response to be as flat as it can get.

Obviously I would just leave them alone if I could but one speaker started giving me issues. I can hear a faint buzzing/scratching sound coming from the tweeter when low frequencies are playing. I think this means the xover frequency has drifted. I'm going to turn the woofers around tomorrow to eliminate "woofer sag", but I want to recap as well. I feel I'm not getting all I can from my 103.2 reference.

So again, what in your opinion is the best practice here? measuring the values is useless because the caps are almost my age, so what would you recommend? Sorry if this is a silly question but this issue comes up all the time as a warning. I simply wonder what's the best solution, if any.

Thanks,
Ronny
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willem-57
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Joined: 18 Jul 2014
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Location: Netherlands

PostPosted: Mon Mar 02, 2015 7:46 am    Post subject: Reply with quote

Hello,
Best is to order new capacitators by Falcon acoustics. Important is that you give the new ones time to break in. By mine speakers it was not that good in the beginning with the allcaps, but now it's getting better and better.
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flextone
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Location: Berlin, Germany

PostPosted: Mon Mar 02, 2015 10:42 am    Post subject: Reply with quote

Thanks Willem.

how much time would you say is necessary?

IIRC reading your post about recapping, you mentioned that your tweeters became 2db louder afterwards. did this change? hope I'm not confusing you with someone else, I've been reading so much about this lately.
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speakerguru
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Joined: 18 Nov 2005
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PostPosted: Mon Mar 02, 2015 4:04 pm    Post subject: Re: Recapping Best Practice? 103.2 Reply with quote

flextone wrote:
I can hear a faint buzzing/scratching sound coming from the tweeter when low frequencies are playing. I think this means the xover frequency has drifted.

Capacitors normally lose capacitance and/or increase in resistance with age. The only way they would let through more low frequencies to the tweeter would be by becoming short circuit. You could check that with a multimeter. You should also try sweeping the tweeter with 2 V sine wave and no crossover connected, to see if the tweeter on its own is OK.
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flextone
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Location: Berlin, Germany

PostPosted: Mon Mar 02, 2015 5:36 pm    Post subject: Reply with quote

Thanks Speakerguru.

I've rotated the woofers last night and wrote down the xover cap values. I'll switch the speakers around to eliminate the amp, and generally keep my ears pealed for that noise. that thing with the tweeter allowing lower frequencies in was just a theory. all I know is that it scratches a bit when I play low frequency material. sounds like a dusty volume pot.

How would I sweep the tweeter with a 2v sine wave btw? with a battery for example?

Regarding the capacitors. I hope I'm not insulting anyone here but I'm honestly not such a romantic that I would want the sound to be as close to the original as possible. I'm mainly after maximizing their performance. for me this means a neutral frequency response, and if possible a "better" tighter sound. In this case, should I insist on the Alcap electrolytes? Won't more modern caps perform better?

Thanks,
Ronny
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speakerguru
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PostPosted: Mon Mar 02, 2015 7:44 pm    Post subject: Reply with quote

flextone wrote:
How would I sweep the tweeter with a 2v sine wave btw? with a battery for example?

You can only get d.c. from a battery, not sine waves. You need a signal generator and a good power amplifier. Set up to get 1 to 2 V rms and apply to tweeter. Sweep through from 100 Hz to 20 kHz up and down. It should sound like a pure smooth whistle. Intermittent crackles could be caused by foreign matter in the voice coil gap.
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flextone
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Joined: 01 Mar 2015
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Location: Berlin, Germany

PostPosted: Mon Mar 02, 2015 8:43 pm    Post subject: Reply with quote

Thanks.

I don't own a dedicated test tone generator but I do own quite a few analog synthesizers which I can program to output rising and falling "sirens" and use a multimeter to check how much volts I'm outputting. but I'm not there yet. if all else fails and it turns out to be the tweeter I'll either take the drivers to a local tech or find a replacement pair I guess.

I still need to test the speakers again now that I've rotated the drivers and swapped sides. hopefully I'll be smarter after this.
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speakerguru
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PostPosted: Mon Mar 02, 2015 11:25 pm    Post subject: Reply with quote

I can recommend this one http://www.esseraudio.com/test-tone-generator-windows-software-generate-test-signal-sine-pink-noise-crest-factor.html
by an ex-colleague of mine


Last edited by speakerguru on Sun Mar 08, 2015 1:06 pm; edited 1 time in total
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flextone
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Location: Berlin, Germany

PostPosted: Sat Mar 07, 2015 8:30 pm    Post subject: Reply with quote

thanks but I'm on a mac...

the buzzing issue seems to have resolved after rotating the drives. although I don't think it was woofer sag because I don't feel any rubbing when pushing in the woofer in parallel with both hands. something might have gotten stuck in some part of the tweeter as you said, and perhaps moving the speaker around from the stands to the work bench and back somehow dislodged it.

I'll keep listening, and eventually recap.
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