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My experience in restoring KEF 104.2 (refurbishing 104/2s)

 
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robertopisa
Junior Contributor 10+


Joined: 14 Dec 2008
Posts: 13
Location: Pisa, Italy

PostPosted: Sat Feb 14, 2009 11:03 am    Post subject: My experience in restoring KEF 104.2 (refurbishing 104/2s) Reply with quote

Dear Kef lovers,

I finished restoring a pair of Kef 104/2s few days ago, and they are running surprisingly good now. I took my time, as I was no hurry (less mistakes). I'd like to describe my refurbishing experience hoping to share some hints with you. Feel free to add more.

Background

I bought the 104.2s at the beginning of November, they were made in 1990/91 (serial number 29xxx). The seller was almost offended when I told him that the ferro-fluid in the tweeters was probably gone. He was the second owner and did not run them at high volumes, and kept them very carefully. Indeed, the 104.2s appeared to be in very good shape, and I paid them more than their ebay price (even if I got a discount). The owner suggested to use a super-tweeter but later I learned that restoring the original tweeters would instead suffice.

When back at home, I discovered that woofers needed the central foam to be replaced. Also, one woofer had a magnet detached. I noticed that the bass was weak, but I thought it was because the kube was not connected (the seller gave me also the kube but he said it was noisy). Opening the 104.2s, I discovered this situation. So I completely disassembled them, and brought the four woofers and the two mid-hi units to an expert here in Italy (Canini Altoparlanti).

I had to wait over a month, but he succeeded in replacing the foams, fixing the magnets and "washing" the tweeters. With the latter term, he meant opening the tweeters, removing the old (partially dried) ferro-fluid, cleaning the dried parts that were sticked on the coils, and putting new ferro-fluid. He gained between 3-6 db for each tweeter in this way. (It costed like buying new tweeters but Kef had no more replacement parts.) Unfortunately, I broke the fixed woofer when assembling it back, but he was kind to fix it again for free. So I was happy with this person.

Lesson learned: independently of the status of the 104.2s (mine appeared very good), prepare yourself to spend some significant money for the woofers and the tweeters. So forget to find a pair of original 104.2s ready to work at their full capabilities. I spent roughly half of the price I paid for the 104.2s. But it is worth investing this money. See the myriad of positive comments in Audioreview.

Disassembling

Opening the bottom hatch is easy, just use some of the screws to take it off from its place. The mid-hi unit is also easy to remove. The top hatch may still remain attached even if the screws are removed. So insert a thin flat screwdriver in the dig between the hatch and the rest of the cabinet, and carefully push the hatch out of its place. Remember to attach all these screws back to their original place with some tape.

Removing the bottom woofer is not much of a problem. After that, you can rotate counterclockwise the force canceling bar that connects the woofers, and remove it from the bottom. The top woofer is now easy to remove since the internal rod for the bar is loose. You need an L-shaped tool to remove the nuts. Note that the top and bottom woofer cannot be switched, so take note of their original position.

Removing the tweeter needs that you put the mid-hi unit on a working surface with the drive units face down. Then, loosen the screw located at the center of the wood strip behind the tweeter. Push the strip to one side, thus exposing the magnet. Lift the tweeter by a little twist and be careful not to touch the cabinet.

Removing the crossover requires first to detach the fast-on connectors of the wires and the white connector for the mid-hi unit. (I also removed the external binding posts.) Take note of the wires attached to the crossover. Detach the crossover from the back wall of the cabinet by removing the six fixing nuts. This requires putting a good part of your arms inside the cabinet (one arm from the hole left free by the top woofer and the other from the bass reflex hole) and proceeding by touch. I used a nut driver that can become L-shaped and that has a friction system that helps removing nuts by a partial rotation back and forth (sorry, I cannot explain it better, but you probably understood).

Checking and restoring

I asked the help of an expert of electronics, friend of mine. The crossover (dividing network as it is called by Kef) was in really good shape. My friend refused to change any component: for example, the number of wire windings in the coils are tailored to balance the components, and thus changing a capacitor could imply also changing some of them. Surprisingly, there are also resistors in the crossover. Anyway, no leakage was found in capacitors.

We decide to rewire internally the speakers. For this, I had to enlarge the hole for leading the wires to the bottom woofer and that for the mid-hi unit (which were later sealed with silicone glue after new wiring was set up). Everything was silver soldered and no fast-on connector was used. We employed 2.5mm OFC wire, except for connecting the crossover to the external speaker binding posts where we used 4mm OFC wire. Speaker cables for the amp-speaker connections also used the same 4mm OFC wire. Hence, speaker drives were directly connected to the crossover and their wire soldered on the terminals. This requires some care for the mid-hi unit, and we left few cm of the original wiring attached to the mid-hi drives. It is better to bind together the wires inside the cabinet, and insert them between the foam for the internal wadding and the internal walls of the cabinet. I did not use any glue since foam naturally re-expands to its original shape and this suffices to tighten the tied wires against the walls.

I replaced the original Mitchell binding posts with more modern ones (e.g. for a picture or this gold plated). I had to enlarge the original cabinet holes, but the new connectors were long enough to let them be soldered outside the cabinet (before soldering, remember to put the nuts on the wires internally to the speaker). On ebay you can find them at good price. I searched for "rhodium pole speaker" but other options are possible.

Apart from the speaker drives restoration as described above, I used silicone grease/oil (different from silicone glue) to renew rubber gaskets in the cabinet and the rubber parts in the drives. Do not use silicone on foam as it will destroy it. Only on rubber parts to make them softer. I noted a significant benefit by performing a soft massage with silicone grease/oil on the rubber surrounding of the mids, since the rubber hardened a bit. As I result, I increased transparency on the midrange since the drive had a better degree of freedom when moving the cone. Same situation for the rubber surroundings of the woofers. Let me repeat: do not use silicone grease/oil on the central foam of woofers. If some silicone grease/oil percolates to the cabinet or the basket, you can remove it using a soft cloth with vinegar.

I used silicone glue to seal where needed (e.g. for the hole enlarged to accommodate the direct wiring from crossover to mid-high assembly unit).

I'm planning to renew the external black surface of the cabinet with black shoe polish cream. The grilles are ok, I had just to glue some of the plugs.

I'm using the spikes that are hidden inside the original rubber feet. Actually, I replaced the original front spikes with taller ones, so the that the speaker becomes slightly reclined backward (my ears are above the level of the tweeters, and in this way the "leaning" speakers have the tweeters aiming at my face when I am sit). The rubber feet are to avoid, according to what I can listen to.

Finally, a comment is in order. When tightening screws, follow a crossing pattern rather than a sequential pattern: start with a screw, then go to the opposite one, then to the one in between the latter two, and so on. Make more rounds if necessary, each tightening more and more. Do not overtighten the woofers since the screws should hold the unit firmly in position on the rubber decoupling grommets without direct contact between the woofer and the speaker cabinet (note taken from the Kef maintainance notes). Also, you risk to detach the magnet since it adds a great pressure to the force cancelling bar that connects the woofers (I had to shorten one of them for the broken woofer that was repaired).

Listening

I own a very good rig, which is transparent and high-resolution: the cdp+pre+amp combo is the new Marantz reference series 11 and the horn speakers are Zingali Overtures 2 on custom stands. After running the restored 104/2s some hours, I asked a musician, friend of mine, to listen. Using a metaphor, the Kefs are elegant Rolls-Royce cars while the Zingali are sport Ferrari cars. Smile

The Kefs have the right pitch and, if you attend concerts of classical music, you can find a similar precise sound, involving your emotions. The Zingalis are modern speakers with high resolution, dynamics, and some mid-hi range empahsis, so they are able to create a precise tri-dimensional stage of the musicians. To my ears, the former are a source of emotion and the latter of fun. I listen to 80% of classical music and vintage pop music on the Kefs, and the rest on the Zingalis. So I will keep both for a while...

I prefer to use Kefs with grilles on and standing on spikes, since they do not sound "boxy" in this way, and the sound is very similar to Quad electrostatic speakers (maybe also the top-level Marantz electronics contributes to this). I agree with those suggesting to place the 104.2 at 50 cm from the back wall. They are very sensible to positioning, so you need some experiments. If you want more punch in the bass, at the price of loosing some transparency on the mid-hi range, remove the feet of the Kefs and put their bottom directly standing on a piece of rigid foam polyurethane with paper surface (it's quite standard for preparing thermal insulation panels in the construction sector) on my concrete floor. I do not miss the Kube at all...

Cheers
Roberto
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pete the bus
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Joined: 30 Apr 2008
Posts: 15
Location: East Kent

PostPosted: Sat Feb 14, 2009 1:21 pm    Post subject: Reply with quote

Thanks for a very informative and interesting post. I have a pair of 104/2's which are needing the bass inner foams repairing(donuts), so the information you have posted here will be of great help.
Peter
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robertopisa
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Joined: 14 Dec 2008
Posts: 13
Location: Pisa, Italy

PostPosted: Thu Feb 19, 2009 10:12 pm    Post subject: Reply with quote

I forgot to say that I put a washer between each spike and the wood bottom of the cabinet, so that spikes can be tighten a bit, getting better precision in the resulting sound.

Cheers
Roberto
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robertopisa
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Joined: 14 Dec 2008
Posts: 13
Location: Pisa, Italy

PostPosted: Thu Aug 20, 2015 6:46 am    Post subject: Reply with quote

I am reviving this post as I had recently a surge of clarification requests and people did not read this post.

Thanks
-Roberto
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speakerguru
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Joined: 18 Nov 2005
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Location: Green Hut, Tovil

PostPosted: Thu Aug 20, 2015 8:38 am    Post subject: Reply with quote

Very useful. I must admit I missed it first time. I have a pair of 104.2s in the garage which I must get around to restoring. I am interested in alternative terminals as mine are missing or broken, a but your links no longer work. Can you fix them?
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robertopisa
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Joined: 14 Dec 2008
Posts: 13
Location: Pisa, Italy

PostPosted: Thu Aug 20, 2015 12:31 pm    Post subject: Reply with quote

This should be the fixed link for binding posts, I think you can also find in other stores.

http://www.hollandlink.nl/index.php?item=--paar_pair&action=article&group_id=33&aid=107&lang=EN



Also the Rhodium version

http://www.hollandlink.nl/index.php?item=--paar_pair&action=article&group_id=33&aid=51&lang=EN


speakerguru wrote:
Very useful. I must admit I missed it first time. I have a pair of 104.2s in the garage which I must get around to restoring. I am interested in alternative terminals as mine are missing or broken, a but your links no longer work. Can you fix them?
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speakerguru
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Joined: 18 Nov 2005
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Location: Green Hut, Tovil

PostPosted: Thu Aug 20, 2015 7:09 pm    Post subject: Reply with quote

Thanks. What are the claimed benefits of rhodium?
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robertopisa
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Joined: 14 Dec 2008
Posts: 13
Location: Pisa, Italy

PostPosted: Thu Aug 20, 2015 7:20 pm    Post subject: Reply with quote

You're welcome. I could not hear any difference, frankly speaking. But they look nice Smile

speakerguru wrote:
Thanks. What are the claimed benefits of rhodium?
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