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Refirbushing Kef 105.1, NEED CROSSOVER SCHEMATIC, etc..
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eardrum
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PostPosted: Mon Dec 08, 2008 10:26 pm    Post subject: Refirbushing Kef 105.1, NEED CROSSOVER SCHEMATIC, etc.. Reply with quote

Greeting to everyone! I've just procured my dream Speakers! The "original"
105's or, what has become the 105.1. They are cosmetically, near perfect! Bass is deep although alittle shy in volume. Mid and top-end are superb! Much improvement from my rebuilt 104aB's, as nice as they now are. Need ALL info that ANYONE can provide on Crossover Rebuilding / Woofer rotating,
Cutting out Protection Circuit, etc. I've been building all things audio since 1969 / DIY'er. But, I need THIS Crossover Schematic. Not, either of the two 105.2 versions posted within this site.
Thank you, in advance. "eardrum"..
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ColinR
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PostPosted: Tue Dec 09, 2008 11:28 am    Post subject: Reply with quote

I think Iíve said this several times and been ignored Sad .

I believe the mid-treble section is the same as the early Ref 105-2 Iíve put on this site.

For the bass section youíll have to find an LCR meter or add a couple of mH to the 105-2 bass inductor values and listen if youíre going to mess around with air-cores and other silly things.

The protection circuitry consists of fuses so use nails, wood-screws or musical bolts Very Happy .

To turn the bass units held by six bolts you'll have to remove all of the other fixings on the bass box to get the front panel off Cool .
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eardrum
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PostPosted: Tue Dec 09, 2008 6:44 pm    Post subject: Refurbishing Kef 105.1 Reply with quote

Hi ColinR, Thank you for your reply! They may in fact be the same. I guess I'll have to get inside the box and see if parts, etc., are in line with that schematic. No air-core inductors desired here, just all new caps and resistors. Noting the apparent low-loss caps in the tweeter section. Looks to me that the front bass baffle board is mortised into the cabinet. Does it have some type of gasket material around the cabinet? Don't really want to remove fuses, I guess but, rather disconnect the pot from circuit, up top. Will let ya know what I find. ThanX.. eardrum...
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speakerguru
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PostPosted: Wed Dec 10, 2008 9:17 am    Post subject: Re: Refurbishing Kef 105.1 Reply with quote

eardrum wrote:
but, rather disconnect the pot from circuit, up top.


The 105 has a very useful clipping indicator but you have to set the switch to tell the speaker what size amplifier you have. There is also a switch position to show the light continuously for setup purposes to make sure both heads are pointing such that your head is within the "listening window". There's also an "off" position or have I misremembered...?
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eardrum
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PostPosted: Wed Dec 10, 2008 6:21 pm    Post subject: Refurbishing Kef 105.1 Reply with quote

Thanks, speakerguru! Yes, I'm aware of the "clipping indicators". I notice you live in Tovil, I think my Quad amp is from there. Did quite a bit of work on it however, won't go into it here. By the way, do you know of a source there, where you are, that supplies all the capacitor values needed in the 105.1 crossover, weather Alcaps or, others? I'm in great need of these parts as I'm noticing a less than Stellar performance with there response curve.. eardrum... Sad
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speakerguru
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PostPosted: Thu Dec 11, 2008 9:01 am    Post subject: Reply with quote

You could try your luck talking to KEF service dept, otherwise you will have to try the Electronic component distributors like Maplin and Farnell in the UK. I don't know about Canada. Sorry.

I'm afraid the Green Hut was one of the casualties of the Gold Peak aquisition of KEF Electronics Ltd in 1991. It was demolished and no longer exists. All that remains is an old Yale key on a keyring with a hand stamped aluminium tag (violins in the background) aaaa-h.
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eardrum
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PostPosted: Fri Dec 12, 2008 4:45 am    Post subject: Refurbishing Kef 105.1 Reply with quote

Thanks, speakerguru, once again! Will get underway with the hunt. Hope there's room on the board for the bigger, PP caps. Don't know if there are
any of the n.p. electrolytics involved in the circuit however, I will look..
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eardrum
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PostPosted: Tue Dec 30, 2008 4:15 am    Post subject: Refirbishing Kef 105.1 Reply with quote

Speakerguru, ARE YOU THERE? I have finally gone inside my set and I've gotta tell ya what I see. Removing the 12" woofer and looking inside to the left wall reveals low-pass board. And on it, from left to right, is a power resistor, an 80uf / 150v np-mylar cap and then there are just "three" of the 120uf caps and a coil at each end of the board. No other room on the board for anything else. When I got into the upper satlelite, there were in fact, 8-caps, 5-coils, 2-resistors and what apears to be another "very small" dipped cap near one of "two" 7uf caps. But, almost all the values are different than what's on your 105.2 schematic.
Also, attacthed to this board is the small sp1062 clipping-monitor board with a 16uf np, a 1000uf electrolytic, a bunch of resistors around the click-pot, 2-diodes and 4-transistors.. Would be happy to send these 4-pics to anyone that may want them. Would STILL love to have THIS Schematic.. eardrum.
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ColinR
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PostPosted: Wed Dec 31, 2008 12:59 pm    Post subject: Reply with quote

A brief analysis of a couple of photographs sent by Shane reveals that the bass and midrange sections have a similar topology to the early Ref. 105-2 (100uF cf 80uF) and the treble section is an acoustic Butterworth a'la KEF Cantata with a parallel notch filter.

So if any Ref. 105 owners want to go further and buy an LCR meter and measure the inductors..............

I'll check them against the nominal values I determined using the non-standard colour codes used for similarly sized components taken from the rest of my collection Cool .
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audiolabtower
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PostPosted: Tue Jan 06, 2009 9:22 pm    Post subject: Reply with quote

I have the schematic. The crossover is 4th order (Linkwitz Riley ?) with all drive unit +s connected through to amp + feed (no phase inversions a la Spendor).

The treble is + to 0.028mH series then 3.3uF series then 0.35mH to ground, then 3.3uF series to fuse to T52 +. There are 2 acoustic butterworth capacitors C9 (across the 0.028mH) and C11 (across the two 3.3uF) available but not used on early Mk1s. Apparently the T52 fundamental resonance was far below the T27 and T33 so the natural rolloff with the steep phase correct total filter was enough in the specially selected tweeters for the reference series. There is also a zobel network across the tweeter (C13 and R3) to ground laid out, but again unpopulated with the selected tweeters in the reference series. I believe the zobel was used in the non selected T52s for the CS9 kit.

The midrange is + to 30uF series, then 1.3mH series , then 10uF to ground, then 2mH to ground, then 100uF series, then 0.25mH series, then a zobel of (7uF in series with 10R) to ground, then the fuse then the B110 +.

The bass is + to 7.0mH series, then 80uF to ground, then 33R to ground, then 360uF series, then 3.5mH series then B300 +.

Both the inductors and capacitors were selected into 2.5% or 1% bands and matched by computer to drive unit pairs so the total gave a centre response down the design axis to meet the tight spec. Thus if replacing capacitors it is important to measure each one and match the capacitance to 0.5% or so to keep the result central. For example my treble caps nominal 3.3uf were in fact 3.55/3.52uF and the other was 3.82uF/3.85uF matched very closely in each speaker when new, obviously a design intent. So when replacing I padded with similar low value caps to make an exact match of the median of the 2 values. Bear in mind also a low value resistor to match the DF at the required frequency is needed when replacing elcaps with polyprop or polyester. Kef used the best elcaps available at that time, I seem to remember d = 0.05 to 0.1. The inductors are not ferrite but iron dust (with a much better saturation performance) and I did not believe there was any point in changing them as they are easily man enough for the job.

Hope this helps.
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proffski
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PostPosted: Tue Jan 06, 2009 11:01 pm    Post subject: Reply with quote

Phew! A great many thanks for your stalwart contribution! Smile
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audiolabtower
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PostPosted: Wed Jan 07, 2009 1:55 am    Post subject: Reply with quote

you're very welcome Very Happy
the best box speakers I ever heard to match electrostatics in the midrange were Spendor BC1s, and the best box speaker to match the magic Spendor midrange but give louder output, more uncoloured and another octave of bass, and as smooth a treble with all the atmosphere and pin point imaging were the 105s.

I took the crossovers out of the boxes when I rebuilt them (many years ago now) and put them in large plastic cases (inductors well separated) near the amps with short speaker leads. All driver sections were separated and 8 speaker leads (2 for the leds easily switched out if wanted) run to each enclosure to the hardwired drive units (and even 8 short leads to the amp outputs). The drive to unit after the crossover is not so critical of speaker wire than the drive from amp to crossover input and I found this short speaker wire trick works well and then took the crossovers out of the Spendors too. It gave the same benefits as normal bi/tri wiring (which I had already done on the BC1s) but more of the same again. Martin Colloms described the technique in detail years ago in HiFi News. It is also easier to have one amp channel driving each crossover section and thus drive unit. Those 105s really were way ahead of their time and still stand up well today.
Cheers,
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ColinR
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PostPosted: Wed Jan 07, 2009 11:01 am    Post subject: Reply with quote

In Shane's Ref 105s SNo 2380 C12 is a 7uF (not 3.3uF) L.L. Electrolytic with a 0.22uF Polyester component at C11 and the Zobel is populated by C13 2.2uF, R3 47R making them a later pair with reduced Quality Control Confused.
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audiolabtower
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PostPosted: Wed Jan 07, 2009 3:00 pm    Post subject: Reply with quote

Hi that's very interesting, but I would not neccessarily say reduced quality control, assuming the values were not a mistake (that is unlikely since each reference was FFT measured before leaving the factory and those values are close to the CS9). My 105s for instance are 3067.

According to the specs as C10 reduced, C12 should increase in value to compensate without the zobel. That batch of tweeters may have had a slightly higher frequency or more pronounced fundamental resonance triggering the requirement the zobel to compensate. The introduction of the zobel needs a different value of C12 and obviously part of the acoustic butterworth circuit was put in too. So it could be great quality control if it made frequency response and audible output the same as the design target? Smile

The AB components were designed to compensate for the effect of the drive unit resonance and voice coil inductance on theoretical croosovers with resistive not voice coil loads etc. It was a great success in the 104ab because the T27 resonance was around 1.2kHz (if my memory is correct) and quite near the 3kHz crossover even though it was 30dB down through the original filter the ab circuit provided a noticeable improvement in the output. The T52 had a larger diaphragm which had the disadvantage of not so good dispersion at 20Khz (solved by a head that could be tilted and rotated) but a smoother response due a lower and better mechanically damped fundamental resonance.

The problem with drive units is repeatability. Kef were the first to use computer simulation in crossover design and computer FFT measurement to match drivers and then use the crossover components to "pull" the drivers into the central design response. They could do it (relatively) cheaply by buying 5% components and then selecting them into 1% bands and using the + and - components to suit the actual drivers the crossover would be used with. It was their version of the BBC autotransformer and "hand measure and select" approach but more cost effective and suited to mass rather than specialist production.

Cheers,
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BobL
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PostPosted: Sun Feb 22, 2009 10:04 pm    Post subject: Reply with quote

Sorry I'm a bit late to this party. I have a pair of R105/1 purchased new 01/09/1978. Serial numbers 2157A 2157B.

I have drawn the diagram as best I could and that is available from http://www.mightyoak.org.uk/kef/R105-1.jpg . If the web master wishes to add this image/data to the web site, please be my guest.

Interesting that my xover is not exactly the same as that described.

I was unable to put values on the inductors so if anyone can fill those in for me, that would be useful, thanks. You may notice that some caps have two different voltages, these are the original and the KEF ok'd replacements.

I have many pictures of crossovers and drivers so again if web master would like them please let me know.

Cheers,

Bob.


Last edited by BobL on Mon Nov 14, 2011 3:38 pm; edited 1 time in total
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