KEF 104/2 restoration and crossover recap

[Boba MosFET]

Replacing the ferrofluid in the tweeters.


Diaphragm comes off with careful use of a sharp knife. I used a chisel shaped blade in an Xacto knife, I think the blade is #18.




After I got everything back together, I tried the tweeters out using nothing more technical than connecting them across the speaker leads with a 3.3uF capacitor. Everything sounded good to me...

Lee.

That yellow material that sealed the dome/coil plate to the magnet, did you replace it? Is there any adhesive used? I've watched a bunch of T33 ferrofluid videos and no one seems to mention this.

 

[Ross6860]

That yellow material that sealed the dome/coil plate to the magnet, did you replace it? Is there any adhesive used? I've watched a bunch of T33 ferrofluid videos and no one seems to mention this.

I re-used the yellow gasket. It's a chore to get them apart without tearing.

I used something like Eileen's Tacky glue on the gasket.

Great speakers, BTW. Up in the top 3 or 4 I have owned.

 

[Boba MosFET]

I re-used the yellow gasket. It's a chore to get them apart without tearing.

I used something like Eileen's Tacky glue on the gasket.

Great speakers, BTW. Up in the top 3 or 4 I have owned.

I agree completely! I rep'd these speakers at a store back in the 80s and couldn't afford them myself. I resolved to get a pair. The ones I bought a couple of years ago had refurbished drivers so they went right into service with a Sumo amplifier. The sound is stellar. Better bass than any other speaker in my collection and perfectly balanced and blended midrange and highs. I have some excellent speakers here but these are my favorite.

My new pair looks a lot better (walnut vs ebony) but the highs will go from decent to brittle in about an hour, which I'm thinking is the ferrofluid sludge building up heat. They're out of service until the new fluid gets here, which is today hopefully.

Do you think that the yellow gasket damage could lead to problems? I'm wondering if it's not just a gasket but also needed as a spacer for proper front-to-back distancing on the voice coil. Or do the locating nubs on the contact sides guarantee the proper spacing?

 

[Ross6860]

I agree completely! I rep'd these speakers at a store back in the 80s and couldn't afford them myself. I resolved to get a pair. The ones I bought a couple of years ago had refurbished drivers so they went right into service with a Sumo amplifier. The sound is stellar. Better bass than any other speaker in my collection and perfectly balanced and blended midrange and highs. I have some excellent speakers here but these are my favorite.

My new pair looks a lot better (walnut vs ebony) but the highs will go from decent to brittle in about an hour, which I'm thinking is the ferrofluid sludge building up heat. They're out of service until the new fluid gets here, which is today hopefully.

Do you think that the yellow gasket damage could lead to problems? I'm wondering if it's not just a gasket but also needed as a spacer for proper front-to-back distancing on the voice coil. Or do the locating nubs on the contact sides guarantee the proper spacing?

There was some minor damage to the "gasket, but I used them anyhow.

The fresh ferro-fluid was literally sucked in by the magnet, so I'm not sure how important the gasket is. You could always measure the thickness and install anything, soft plastic, a true gasket, paper, etc., if you think it is also acting as a spacer.

My cabinets were beat up, and no grills, so I sold them. They still sounded fantastic.

 

[rickb119]

the highs will go from decent to brittle in about an hour, which I'm thinking is the ferrofluid sludge building up heat. They're out of service until the new fluid gets here, which is today hopefully.

If the ferrofluid doesn't fix the brittleness, you might try a different amp. My 104/2's (with new fluid/caps) sound a bit bright when using my Sansui AU-919, but oh so sweet with my B&K ex4420 (mosfet) amp. Many prefer the smoother mosfet sound with their KEF's.

After replacing the fluid in mine, the gasket was far from perfect. I don't think it affects the sound.

 

[leesonic]

I don't think it's a gasket. It's a layer of double sided sticky "tape". If you're lucky enough to remove the dome without disturbing it too much, and it's still got some sticky left to it, simply re-use it. Don't scrape it all away unless you're planning on replacing it.

Glad to see this thread is still helping out 104/2 owners. Maybe I'll get a pair of my own some day?

 

[Boba MosFET]

If the ferrofluid doesn't fix the brittleness, you might try a different amp. My 104/2's (with new fluid/caps) sound a bit bright when using my Sansui AU-919, but oh so sweet with my B&K ex4420 (mosfet) amp. Many prefer the smoother mosfet sound with their KEF's.

After replacing the fluid in mine, the gasket was far from perfect. I don't think it affects the sound.

Yes I'll try a few other amps, good idea. My Perreaux is a mosfet but it's probably long overdue for a refresh. I have a little hum coming through the speakers and when I got it there was a blown fuse on one channel. It does sound good through my Polk Monitor 7b's though.

 

[Boba MosFET]

I don't think it's a gasket. It's a layer of double sided sticky "tape". If you're lucky enough to remove the dome without disturbing it too much, and it's still got some sticky left to it, simply re-use it. Don't scrape it all away unless you're planning on replacing it.

Well thats good to know. At some point I'll take some measurements and have some proper sticky tape cut with a knife plotter. My FerroTec showed up today and I'm too impatient to wait for new sticky tape, so I'm just going to plow ahead on the project and start breaking stuff.

Glad to see this thread is still helping out 104/2 owners. Maybe I'll get a pair of my own some day?

You will enjoy them. Perhaps we'll get a GoFundLee started for you?

While you're in the room, can you explain if there are any circuit differences between the earlier XO (the ones with rubber surround woofers) and the later (biamp and foam surround)? I've heard there was a difference in the number of caps between the two boards.
And I thought all the biamp ones were reissues from '90 or later and they were all Raymond Cooke Special Edition, but mine lack the brass plaque - are they still RCSE?

 

[CHPf]

KEF 104/2 – Crossover Rebuild: Myths and (my) Reality

If you are contemplating recapping your KEF 104/2 speakers, DO!
If you're hesitant (KEF put so much efforts to match capacitances and speakers so any change will affect the sound...) or are confused about all the contradictory information (MKP Vs. Electrolytics, ESR values and Capacitance drift...), you're not alone!
After many years of Audio DIY, I did a budget friendly-upgrade recapping of my beloved KEF 104/2 and the result is beyond my expectation.

Background:
I bought a pair of KEF 104/2 mono-wired speakers (1990 build) in 2015. Tweeters were damaged, and bass drivers had rotten suspensions. I replaced all suspensions, repaired the T33 tweeter, added new ferrofluid, and updated the cabinets to mahogany. I skipped recapping the crossover back then.

10 Years Later:
The right speaker sounded muddy. Since the Ferrofluid was only 10 years old, and I decided it was now time for a full crossover recap.

Recap Strategy:
To keep budget low, whilst maximizing impact, I focused on capacitors critical to crossover frequencies:

• Tweeter (C13–C16): Replace with MKP polymer film caps
• Mids (C6, C7, C8, C12): Replace with Electrolytics ; bypass C6+C7 with 2µF film, use film capacitor for C12 low-loss
• Lows (C2, C3): Replace with Electrolytics.

Observations & Myths:

• Ferrofluid: Old ferrofluid really kills clarity, even after "only" 10 years!
  Replacing it restored clarity and detail, not only to the failing speaker but to both.
• ESR Values : ESR was very low on all capacitors (max value 0,1 Ohm at 100kHz =~ 0,4 Ohm at 1kHz).
  On the KEF104/2 speakers, there is no need to add any resistance in series to the MKPs, since the initial ESR values are very low.
• Capacitance: Capacitance of all capacitors had drifted positively by 8–38% (most between 12-18%), affecting crossover accuracy.
  KEF's orginal 2% tolerance on capacitance is no longer valid on these vintage 30+ years speakers.
• Recap Impact:
  MKP caps in tweeter further improved clarity, but only slightly, without altering the sound.
  Mids and lows saw most dramatic improvement: vocals and instruments became vivid and lifelike.
  Aging C6 and C7 constrained the mid-range, despite the low ESR and "only" 15% capacitance drift.

Conclusions & Tips:

1. Replace ferrofluid first; redo every ~10 years (~70% of improvement).
2. Do, at least, the Essential recap caps: (~25% improvement)
   
   • Lows: C2, C3
   • Mids: C6, C7, C8, C12
   • Tweeter: C13–C16
3. My recommendation: Use high-quality electrolytic caps for >20µF, and film caps for smaller values to maximize clarity (~5% improvement).
   No need for additional resistance in series to the MKPs
4. Optional: Bypass midrange in-line caps (C6+C7) with 1–2µF film for extra detail. (I did)
5. Replacing all other caps can future-proof the speakers. (I did not, yet, but have all capacitors at home)

Result:
After replacing ferrofluid and essential caps, the 104/2s are stunning—warm, detailed, and alive.
Total cost: €134 for both speakers - including ferrofluid.
By far the best investment to revive these legendary speakers.
For those interested I attach a small report with pictures and the list of capacitors.
Wishing you success with your recapping project and a lot of long-lasting enjoyment thereafter!

 

[absolve2525]

KEF 104/2 – Crossover Rebuild: Myths and (my) Reality

If you are contemplating recapping your KEF 104/2 speakers, DO!
If you're hesitant (KEF put so much efforts to match capacitances and speakers so any change will affect the sound...) or are confused about all the contradictory information (MKP Vs. Electrolytics, ESR values and Capacitance drift...), you're not alone!
After many years of Audio DIY, I did a budget friendly-upgrade recapping of my beloved KEF 104/2 and the result is beyond my expectation.

Background:
I bought a pair of KEF 104/2 mono-wired speakers (1990 build) in 2015. Tweeters were damaged, and bass drivers had rotten suspensions. I replaced all suspensions, repaired the T33 tweeter, added new ferrofluid, and updated the cabinets to mahogany. I skipped recapping the crossover back then.

10 Years Later:
The right speaker sounded muddy. Since the Ferrofluid was only 10 years old, and I decided it was now time for a full crossover recap.

Recap Strategy:
To keep budget low, whilst maximizing impact, I focused on capacitors critical to crossover frequencies:

• Tweeter (C13–C16): Replace with MKP polymer film caps
• Mids (C6, C7, C8, C12): Replace with Electrolytics ; bypass C6+C7 with 2µF film, use film capacitor for C12 low-loss
• Lows (C2, C3): Replace with Electrolytics.

Observations & Myths:

• Ferrofluid: Old ferrofluid really kills clarity, even after "only" 10 years!
  Replacing it restored clarity and detail, not only to the failing speaker but to both.
• ESR Values : ESR was very low on all capacitors (max value 0,1 Ohm at 100kHz =~ 0,4 Ohm at 1kHz).
  On the KEF104/2 speakers, there is no need to add any resistance in series to the MKPs, since the initial ESR values are very low.
• Capacitance: Capacitance of all capacitors had drifted positively by 8–38% (most between 12-18%), affecting crossover accuracy.
  KEF's orginal 2% tolerance on capacitance is no longer valid on these vintage 30+ years speakers.
• Recap Impact:
  MKP caps in tweeter further improved clarity, but only slightly, without altering the sound.
  Mids and lows saw most dramatic improvement: vocals and instruments became vivid and lifelike.
  Aging C6 and C7 constrained the mid-range, despite the low ESR and "only" 15% capacitance drift.

Conclusions & Tips:

1. Replace ferrofluid first; redo every ~10 years (~70% of improvement).
2. Do, at least, the Essential recap caps: (~25% improvement)
   
   • Lows: C2, C3
   • Mids: C6, C7, C8, C12
   • Tweeter: C13–C16
3. My recommendation: Use high-quality electrolytic caps for >20µF, and film caps for smaller values to maximize clarity (~5% improvement).
   No need for additional resistance in series to the MKPs
4. Optional: Bypass midrange in-line caps (C6+C7) with 1–2µF film for extra detail. (I did)
5. Replacing all other caps can future-proof the speakers. (I did not, yet, but have all capacitors at home)

Result:
After replacing ferrofluid and essential caps, the 104/2s are stunning—warm, detailed, and alive.
Total cost: €134 for both speakers - including ferrofluid.
By far the best investment to revive these legendary speakers.
For those interested I attach a small report with pictures and the list of capacitors.
Wishing you success with your recapping project and a lot of long-lasting enjoyment thereafter!

Awesome! Saved for later.

 

[Metamodern]

KEF 104/2 – Crossover Rebuild: Myths and (my) Reality

If you are contemplating recapping your KEF 104/2 speakers, DO!
If you're hesitant (KEF put so much efforts to match capacitances and speakers so any change will affect the sound...) or are confused about all the contradictory information (MKP Vs. Electrolytics, ESR values and Capacitance drift...), you're not alone!
After many years of Audio DIY, I did a budget friendly-upgrade recapping of my beloved KEF 104/2 and the result is beyond my expectation.

Background:
I bought a pair of KEF 104/2 mono-wired speakers (1990 build) in 2015. Tweeters were damaged, and bass drivers had rotten suspensions. I replaced all suspensions, repaired the T33 tweeter, added new ferrofluid, and updated the cabinets to mahogany. I skipped recapping the crossover back then.

10 Years Later:
The right speaker sounded muddy. Since the Ferrofluid was only 10 years old, and I decided it was now time for a full crossover recap.

Recap Strategy:
To keep budget low, whilst maximizing impact, I focused on capacitors critical to crossover frequencies:

• Tweeter (C13–C16): Replace with MKP polymer film caps
• Mids (C6, C7, C8, C12): Replace with Electrolytics ; bypass C6+C7 with 2µF film, use film capacitor for C12 low-loss
• Lows (C2, C3): Replace with Electrolytics.

Observations & Myths:

• Ferrofluid: Old ferrofluid really kills clarity, even after "only" 10 years!
  Replacing it restored clarity and detail, not only to the failing speaker but to both.
• ESR Values : ESR was very low on all capacitors (max value 0,1 Ohm at 100kHz =~ 0,4 Ohm at 1kHz).
  On the KEF104/2 speakers, there is no need to add any resistance in series to the MKPs, since the initial ESR values are very low.
• Capacitance: Capacitance of all capacitors had drifted positively by 8–38% (most between 12-18%), affecting crossover accuracy.
  KEF's orginal 2% tolerance on capacitance is no longer valid on these vintage 30+ years speakers.
• Recap Impact:
  MKP caps in tweeter further improved clarity, but only slightly, without altering the sound.
  Mids and lows saw most dramatic improvement: vocals and instruments became vivid and lifelike.
  Aging C6 and C7 constrained the mid-range, despite the low ESR and "only" 15% capacitance drift.

Conclusions & Tips:

1. Replace ferrofluid first; redo every ~10 years (~70% of improvement).
   • Lows: C2, C3
   • Mids: C6, C7, C8, C12
   • Tweeter: C13–C16
2. My recommendation: Use high-quality electrolytic caps for >20µF, and film caps for smaller values to maximize clarity (~5% improvement).
   No need for additional resistance in series to the MKPs
3. Optional: Bypass midrange in-line caps (C6+C7) with 1–2µF film for extra detail. (I did)
4. Replacing all other caps can future-proof the speakers. (I did not, yet, but have all capacitors at home)

Result:
After replacing ferrofluid and essential caps, the 104/2s are stunning—warm, detailed, and alive.
Total cost: €134 for both speakers - including ferrofluid.
By far the best investment to revive these legendary speakers.
For those interested I attach a small report with pictures and the list of capacitors.
Wishing you success with your recapping project and a lot of long-lasting enjoyment thereafter!

Thanks for the highly detailed info! Very practical using film caps in some locations.

 

[Boba MosFET]

I bought a pair of KEF 104/2 mono-wired speakers (1990 build) in 2015. Tweeters were damaged, and bass drivers had rotten suspensions. I replaced all suspensions, repaired the T33 tweeter, added new ferrofluid, and updated the cabinets to mahogany. I skipped recapping the crossover back then.

I'm assuming you started with ebony cabinets because I wouldn't change teak or walnut. Do you have pics of the transformation process? Or at least pics of the finished product.