Kef reference model three-two crossover upgrades.

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Nico M

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Hi all,

This is my first crossover upgrade. I own kef reference model three two loudspeakers, which i like for the most part. The first problem i had with them, is the mid/highs being to aggressive and "bright" with female singers siblings. I liked the soundstage, and the airy sound of the speakers. The mids seemed OK, but in retrospect nothing to write home about.

I did watch several video's of GR research, and the owner of that channel does a lot of meaningfull upgrades. He seems to like sonicaps, and mills resistors, so i decided to use just that.
As sending 2 times of 70 pounds worth of loudspeaker to Texas across the world was not the most easy thing to do, i decided to attack the crossover myself. The first series capacitor of the tweeter was a 4,4uf  yellow bennic polycap, and this i replaced with a sonicap of the same value. Also the first series capacitor of the mids was a blue bipolar cap of 8uf, which also was replaced with a sonicap. I worried a bit about the esr, but the difference between them wasn't alarming, 0.04ohms for the sonicap, and 0.07ohm for the bennic bipolar, so i just swapped them. Also all mills resistors in the mids and highs. These loudspeakers do gave a internal setting for switching in 0.5db steps in the mids, and highs, but i left everything alone for the first tryout.

The results receded my expectations. Initially the highs, and mids seemed a bit aggressive, but with less of a "sharp edge" and after about 60 hours of playing they seem to smooth out more and more.  My soundstage is greatly improved in depth layers. But the transparency of the mids is impressive. Wow, never expected this.
The other thing that happened,  is that vocals are much less warm sounding, but more accurate and less chesty. I would like the upgrade the rest of the crossover from the midbass, and bass drivers, but I'm not sure which brand of parts to use. The crossover is quite full of high value electrolytic capacitors, which can't be replaced by sonicaps.  Not sure what to choose next, because i would like to improve the layers in my midbass as well. The highs and mids are so dramatically improved, it seems silly not to give the rest of the e crossover the same treatment. But where to go from here, and what would my best option be?
Bypass the electrolytic's in the low part of the crossover with sonicaps? To get some layers, and speed in the bass?

Suggestions are appreciated...

Tyson

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Re: Kef reference model three-two crossover upgrades.
« Reply #1 on: 25 Aug 2021, 04:58 pm »
I'd replace the electrolytics with the Erse line that Danny sells or the Mundorf line that Jeff sells, and bypass them with a small value Sonicap of .01uf.  That will clean up your bass quite a bit. 

Next, look at your midrange and high frequency inductors - definitely swap out the existing inductors on the mids/highs with high quality air core inductors like the ones from Erse, Solen, Jantzen, Dayton or Madisound.

Finally, the bass inductors (if there are any), will probably be too large a value to use an air core inductor, I'd recommend replacing whatever is in your speakers with some high quality I-Core inductors from Erse, something like this - https://www.parts-express.com/ERSE-Super-Q-3.0mH-16-AWG-500W-Inductor-266-912
« Last Edit: 25 Aug 2021, 06:21 pm by Tyson »

Nico M

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Re: Kef reference model three-two crossover upgrades.
« Reply #2 on: 25 Aug 2021, 05:40 pm »
Hi Tyson,

Thanks for your suggestions. First i think i have to contact Kef, for a crossover schematic. For the value of the iron core inductors. Otherwise it's impossible to know what to buy for replacements. There is however not too much room on the crossover. But we will see what is possible. I look into the caps you suggested. Thanks...

P.s. i cannot upload an image, still won't work.

Tyson

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  • Audio - It's all a big fake.
Re: Kef reference model three-two crossover upgrades.
« Reply #3 on: 25 Aug 2021, 06:22 pm »
Hi Tyson,

Thanks for your suggestions. First i think i have to contact Kef, for a crossover schematic. For the value of the iron core inductors. Otherwise it's impossible to know what to buy for replacements. There is however not too much room on the crossover. But we will see what is possible. I look into the caps you suggested. Thanks...

P.s. i cannot upload an image, still won't work.

That's true, better parts are generally bigger so you might be limited by what you can fit.

Norman Tracy

Re: Kef reference model three-two crossover upgrades.
« Reply #4 on: 25 Aug 2021, 10:49 pm »
Great journey you are on Nico M, thanks for sharing. I absolutely adore the acoustic and industrial design of KEF’s Reference 3 so it’s a worthy platform for all these goodies IMHO.

This comment post cap and resistor upgrade I find quite interesting “But the transparency of the mids is impressive. Wow, never expected this. The other thing that happened, is that vocals are much less warm sounding, but more accurate and less chesty.”

Here is a theory about ‘less warm, but more accurate’. On AC and in Danny’s videos a lot of talk about ‘fast’ caps as one moves up the cap quality ladder from electrolytic, to polyester, to polypropylene, and onto the exotics. From an electrical engineering view the measurable (easily measurable) parameter here is DA, Dielectric Absorption. I believe it is what is causing Nico’s warmth becoming transparency and accuracy observation. Capacitors work by storing electrical charge in their plate + dielectric structure. The lower a cap’s DA number the better it is at quickly and completely storing then releasing that charge. One tests this by connecting the cap to a DC source and charging it to a voltage within its rating. Then disconnect it and short circuit it to ground. In theory all the charge will drain off and be gone. In actual real world parts the voltage goes to zero while shorted to ground, then when open circuited (or connected to a very high impedance like a good voltmeter or oscilloscope probe) we see some of the voltage slowly return. That why it is called Dielectric Absorption because some of the current remained absorbed in the plate + dielectric structure and once presented with a high impedance it leaks out and while it does a slowly building voltage is observed. In an amplifier + crossover + speaker drivers + enclosure load circuit this plays out as the music goes from positive voltage to negative hundreds and thousands and tens of thousands of times a second the current from DA is released later in time vs. ideal. Frequency is inversely proportional to time period so slowly releasing charge is transposed to a lower frequency. Extra energy (energy not present in the original spectrum of signal being reproduced, therefore distortion) further down in the midrange is heard as ‘warmth’ and ‘chesty’. Lower the DA with improved parts and the transposed in frequency/time energy is reduced and one hears “vocals are much less warm sounding, but more accurate and less chesty.” As an experienced listener Nico also recognizes “transparency of the mids” becomes “impressive” due to the reduction of misplaced in frequency/time energy resulting in overall lower distortion.

Happy listening, and soldering, and listening…..

Nico M

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Re: Kef reference model three-two crossover upgrades.
« Reply #5 on: 26 Aug 2021, 09:24 am »
Hi Norman,

Thanks for your insights! Sounds like a logical explaination to me. I too like this speakers a lot. I have the revised version of 2001, in cherry finish. Drop deap gorgieus, but after developing my listning skills,  way too "warm" and with not enough resolution. The mids and highs are very transparant after the tweaks.
I,m still wondering if it would benefit further from bypassing the series sonicap from 4,4uf with a small value sonicap (highs), and the 8.0uf mids sonicap, bypassing with another small value sonicap?

What could the benefits be? Even better siblings control? Or could faseshift become a problem?

Nico M

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Re: Kef reference model three-two crossover upgrades.
« Reply #6 on: 10 Oct 2021, 03:03 pm »
Update:

I did some bypass capacitor experiments with a  older set of Kef C60's which i use to test equiptment.
The only thing i did was bypass the e caps in the crossover with a small 10nf value wima filmcap which i had in my stash.

The results far exeeded my expectations. The story of DA beeing a problem, is proven now. These old speakers transformed from a slow, warm sounding muffled speaker to a highly enjoyable set with lots of speed, great imaging and decent details.

So i ordered al new Sonicaps, for bypassing the e caps in my Kef reference model three two.
Also i ordered some Mundorf e caps for the higher values in my crossover,  at least what jeff had in stock.
For now i will just do the bypass upgrade, listen to them for a month, and report back.

Nico M

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Re: Kef reference model three-two crossover upgrades.
« Reply #7 on: 12 Oct 2021, 09:21 pm »
Big thanks to Soniccraft (Martin), for shipping my parts, and helping me out there.
The Mundorfs are also in, at least the value's that where in stock. And all 22 sonicaps (bypass) for both crossovers are in.
I know these need to burnin at least a couple of 100 hours, but the first impressions are very encouraging.
The resuming chestiness in the lower vocal region is gone! This was a major problem,  and really stood out in a negative way. It bothered me...
Voices sound natural now. Also i have already real bass layers, and the whole spectrum gained a lot of speed.
It is a really different entertaining and pretty fast speaker now. Very easy to listen too.
Chuffed to bits with it.

iaRIVR

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Re: Kef reference model three-two crossover upgrades.
« Reply #8 on: 25 Jan 2022, 01:58 pm »
Did you happen to get a schematic for the model three-two's? I'm considering a similar project.

Nico M

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Re: Kef reference model three-two crossover upgrades.
« Reply #9 on: 10 Feb 2022, 11:15 pm »
No i did not get a response from Kef UK on my request for a schematic.
I did one final change to the crossover.
After two months of listening, i decided i needed just a little more warmth in the mid/highs, and highs.
So i removed both the sonicaps bypass from the first series cap in the tweeter circuit, and did the same for the mids. I replaced these with myflex copper in foil caps. Ordered direct from Poland. These are very big, and where difficult to place.

The burnin time is very, very long for these caps. Specially in the tweeter circuit. It took forever to get real transparancy in the highs. But after almost 6 weeks of regular use, it al comes together now. The mids and highs have a smoother presentation, very slightly rolled off, but with great detail and a fantastic soundstage. It sounds more realistic and real. As if someone is actually playing in your living room.

Highly recommended...
« Last Edit: 11 Feb 2022, 07:40 am by Nico M »