SpeakerTalk

[Lee in Montreal]

I will write this little thread as a blog, trying to depict my little aventure with my Kef 105/2(s). As I mentionned a few weeks ago, I purchased a set of faux-105/2 with custom made bass modules, emptied heads and custom crossovers. And in all honesty, the sound is quite impressive. Deep bass, overall good tonal balance, with perhaps a bit too much of low midrange. But overall, delightfull.

Today I received some orphan 105/2 components from two sources. Ken provided me with two bass modules, including crossovers. Joe provided me with two heads and their crossovers and harness.

I slapped everything together and started a CD. First step was to check if that little led worked. I tested the aiming function, it worked after a few seconds trying to get enough power from the music. Speaking of music... Ouch. Doesn't sound as good as the other Franken Kef: bass is muddy and not as deep, mediums are way too present. So, remembering that there are two versions of crossovers, probably matched to two versions of medium drivers, I decided to check what's inside the bass modules.

1- The heads came with crossovers from the 1st generation (only C12 is shorted) w/sp1119 serial # 3179. Some condensers have been swapped for funky candies.

2- Modules have 2nd generation crossovers

3 - The boards' male connectors to the heads are different



4-3 The loom's connectors from the crossovers to the head are different from a serie to another.

_________________
Current line up
2 sets basic Kef 104/2
2 sets bi-wire Kef 104/2
Plenty of KEF components for a few fun builds

[Lee in Montreal]

In the mean while I swapped a B300. Upon inspection, it seams the unit that came out of the Franken Kef is a Construction Set B300 as the paper sticker on the magnet seems to indicate. Even after swapping woofers, the real 105/2 still seems soft and dead, while the Frankens are very lively, fast and have lots of energy. After I purchase an LCR multimeter I will measure all there sets of crossovers (2 sets of Kef and the custom Franken). And will bring the stock filters back to spec. And as I like so much the sound of the Franken, I may replicate it with proper high quality components, and kick ass coils.

As Collin highlighted a few days ago with another person, it is possible that the caps at the entry of the bass channel are out of spec and are simply altering out the bass signal. Will measure tonight with my newly purchased LCR multimeter.


_________________
Current line up
2 sets basic Kef 104/2
2 sets bi-wire Kef 104/2
Plenty of KEF components for a few fun builds

[Lee in Montreal]

The quest for the emasculatd bass continues. The wood of the cabinet is very nice and well preserved. I cleaned it and oil it. Gorgious. They don't look like 30 years old cabinets anymore. Job done. But under carefull investigation of the woodwork, I noticed a crack/split between the front panel and a side panel. So, I removed the B300 and the foam. Inserted a light inside the cabinet. There was, probably, my bass leak. A 1mm crack by 3" long.

It reminded me of an article, a few years back, when an audio journalist had a set of high end speakers to test. He was flabergasted by the quality of the bass. And as tests usually last a few weeks, he kept on enjoying the music for days, and days. Until the extended bass started disapearing... Maybe, he thought, he got used it. But other critics noticed the same thing. After carefull inspection, somebody noticed the woofer's screws were slowly, but surely, unthreading, allowing an air gap in the sealed enclosure. They retightened the screws, the bass came back. They called the manufacturer explaining this little glitch, and from that days, all bass driver bolts were installed with Loctite.

In my case, it is now a matter of trying to reglue this section and let it sit overnight. In the morning I will use some sealant to completely caulk all corners. And while am at it, I will use some heavy tar sections on all panels. I am amazed it was not done at the factory.

Lee
_________________
Current line up
2 sets basic Kef 104/2
2 sets bi-wire Kef 104/2
Plenty of KEF components for a few fun builds

[speakerguru]

[Lee in Montreal]

Hi Collin

I don't think it was a Monday morning/Friday afternoon defect that went thru quality control unnoticed. The side panel simply unglued itself in the corner, maybe due to humidity. After all, it is cheap 30 year old fiber board. Maybe not enough glue to begin with. No big deal. Noneheless, I am taking notes for when I build my own enclosures. Lots of glue and bracing.

Now that the clamps are removed and the drivers put back in. The bass is tighter and stronger. A major imrovement since yesterday's disapointement. The current outcome is that I now know that all drivers work properly (no coil rub, no corrosion on B300, good heads). I am happy I own some piece of audio history, and have spares to experiment.

I have two pre amps now. NAD 1300 with lots of "sound shaping" knobs (bass, treble, frequency switch points, sub freq, 50Hz bump - great for that extra bass you don't hear but just feel) and a 1979 Technics SE-9070 with no tone controls at all. So, I will see what happens if I connect a Kube 200, which was not designed specifically for the 105/2. If it works, it works, if it doesn't, then it goes back in its box.

Technics se-9070 Flat Serie preamp with DC output

_________________
Current line up
2 sets basic Kef 104/2
2 sets bi-wire Kef 104/2
Plenty of KEF components for a few fun builds

[ColinR]

Who's Collin?

speakerguru aka Henry, see page ten of KEF REFERENCE SERIES MODEL 109 - THE MAIDSTONE - INSTALLATION MANUAL.

proffski aka Andrew, see his avatar.

me well there is one photograph on the Internurd, but I'm not telling .

[Lee in Montreal]

[Lee in Montreal]

Still working at identifying the source for that lack of bass.
While listening to some Paul Weller's Style Council vinyl. Life's good.[/img]
_________________
Current line up
2 sets basic Kef 104/2
2 sets bi-wire Kef 104/2
Plenty of KEF components for a few fun builds

[speakerguru]

[Lee in Montreal]

[Lee in Montreal]

One incident that forgot to report is that yesterday, when playing one faux and one real 105/2 on the left and right channels (only two speakers hooked the 135wpc power amp), I could play the faux 105/2 at very loud level, but the real 105/2 would kinda trip/clip at much less volume.

Can Collin or Speaker Guru if it is the symptom of a failed crossover where, perhaps, some capacitor are way out of specs, allowing low frequency to the B110, per exemple.

I trully think that my next step is to spend a few $100 on quality caps and redo a set of crossovers, to specs as close as possible. Luckily, I have Solen in my backyard (30 minutes drive) and I may ask to spend an afternoon matching components. My capacitance meter is precise to the 0.1%. It might help. Why not mentioning inductors and resisitances? Simply because I think they usually don't shift out of specs as easily as caps.

I have worked all day long to pack all business orders for the past week and I am going with the boys to have a few pints of Bass tonight. So tomorrow will be ideal for spending some quality time with the PCBs... (BTW I work from home as my business is based in my basement).

Lee
_________________
Current line up
2 sets basic Kef 104/2
2 sets bi-wire Kef 104/2
Plenty of KEF components for a few fun builds

[speakerguru]

It could be a crossover fault, but..................

There are 5 lines to the protection circuit. One thermal for each unit, an overvoltage and a woofer overexcursion. The woofer excursion was not popular. Most people seemed to prefer the odd noise from the woofer rather than the whole system cutting out. I think it was removed from later models. I think it's the red wire from the base to head.

What's the maximum voltage swing of your amplifier?

[SaSi]

It may be a long shot but it could be a capacitor in the crossover. I have a faulty Calinda crossover - fixed the hf part that had a bad capacitor - but the low frequency network seems to have a capacitor that is marginal. At low levels it works fine. Increasing volume causes some clipping sort of sounds but the speaker doesn't vibrate that much to justify clipping from excursion.

I replaced it (temporarily - don't shoot me) with a Corelli crossover and the clipping "effect" is gone - although it sounds a bit unbalanced left to right at the moment.

[Lee in Montreal]

T follow-up on the clipping, it dosn't happen with excessive excursion of the B300. I repeated the the test, and on both 105s it is the the B100 that clips due to low frequencies reaching the driver. Anyway, last night I took some measurements of first generation board (4caps in parallel on the bass channel, and shorted C12). It is an understatement that measures were allover the place. So, I redid the tst this morning and came upwith same specs. here's how it goes - notice that readings were taken with caps on the PCB.

Bass section
R1 reads at 0.2 Ohms, basically it seems to indicate that the short comes from the "breaker/relay in parallel, and that it bypasses the 680 Ohms resistance.
C1+C2+C3+C4 (4x120µF) read 560µF
C5 (60µF) reads 97µF

Medium section
C6 (20µF) reads 97µF
C7 (7µF) - unstable reading --> 7 to 100
C8 (80µF) reads 106µF
C9 (10µF) reads 97µF

and so on... so it is currently pretty werd
_________________
Current line up
2 sets basic Kef 104/2
2 sets bi-wire Kef 104/2
Plenty of KEF components for a few fun builds

[ColinR]

The KEF S-STOP circuit is a parasitic design in parallel with the crossover, they do not interact (or affect the sound) unless there is a fault condition.

So what's the maximum voltage swing of your amplifier?

The S-STOP may operate a little too soon for some, but some of those who have disabled it tend to be the same ones that bleat at me regarding sources of replacement drive units .




C8 is always cooked in Ref 105-2s .
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