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Do electrolytics values stay constant ?
Do electrolytics values stay constant ?
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Old 20th September 2019, 03:23 PM   #11
lolilol1975 is offline lolilol1975
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Quote:
Originally Posted by Galu View Post
In my opinion, there's nothing wrong with the 'sound' of properly chosen electrolytics.

In fact, replacing electrolytic capacitors with film capacitors can upset the sound balance of vintage speakers because of changes in equivalent series resistance (ESR).
Well, I'm not going to lie, I don't like the sound of these speakers at the moment. They sound dull, lifeless, they lack detail (no air around instruments) and the treble can sound harsh. This certainly isn't the case with even entry level 2 way speakers I have. So I assume that's not how these well regarded reference speakers are supposed to sound. My personal experience is too many components in the signal path, and in particular electrolytics, tend to do that.
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Old 20th September 2019, 03:27 PM   #12
lolilol1975 is offline lolilol1975
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Originally Posted by analog_sa View Post
One option is to build external crossovers in case you like the speakers enough. It is very easy to get carried away though
Yes but I don't have the knowledge and experience for that.
I would have to measure the drivers and I've never done that. I would screw up.
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Old 20th September 2019, 04:31 PM   #13
lolilol1975 is offline lolilol1975
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Originally Posted by analog_sa View Post
One option is to build external crossovers in case you like the speakers enough. It is very easy to get carried away though
Yes but I don't have the knowledge and experience for that.
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Old 20th September 2019, 04:32 PM   #14
Galu is offline Galu  Scotland
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Originally Posted by lolilol1975 View Post
I don't like the sound of these speakers at the moment. They sound dull, lifeless, they lack detail.
It is probable that the original electrolytics have aged substantially, changing in both capacitance and ESR.

Replacement electrolytics, as included in the Falcon set, will hopefully restore the factory fresh sound.

Good luck with the renovation and please report back on your findings.

P.S. I'm no fan of overly complicated crossover circuits myself!

P.P.S. Are the KEFs a recent acquisition, or have you owned them from new?
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Old 20th September 2019, 05:13 PM   #15
Galu is offline Galu  Scotland
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If you studied my earlier diyAudio link, you will have come across this useful analysis of the complex 105/3 crossover circuit.

I presume your French is as good as mine!
Attached Images
File Type: jpg 105.3 Analysis.jpg (244.4 KB, 103 views)
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Old 20th September 2019, 06:29 PM   #16
Galu is offline Galu  Scotland
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Quote:
Originally Posted by lolilol1975 View Post
My personal experience is too many components in the signal path, and in particular electrolytics, tend to do that.
If the straightforward replacement of all the capacitors fails to produce the open and detailed sound you seek, then it may be interesting to recreate the crossover MINUS the various add-ons such as the impedance linearisation, contour and shelving networks shown in the above analysis.

This would leave the basic high pass, band pass and low pass filters, and produce a crossover with the low component count that you favour!

I wonder how that would sound?
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Old 20th September 2019, 06:32 PM   #17
lolilol1975 is offline lolilol1975
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Originally Posted by Galu View Post
If you studied my earlier diyAudio link, you will have come across this useful analysis of the complex 105/3 crossover circuit.

I presume your French is as good as mine!
He he, I am the guy who put the original photo in that forum and that's what one of the guys responded. I am not sure why the speakers need such a complicated circuit. Anyway I can translate for you, from top left to bottom right:

Tweeter
Linearisation to the tweeter resonance freq. (not sure what that means)
Amortized Band cut ( <-- no idea why this is necessary )
3rd order pass high

For the Mf UniQ
2nd order band pass
Networks to compensate the resonance freq. of impedance (don't know what that means)
Shelving

For the Mf Up and Low woofers
2nd order low pass
Linearisation of impedance

For the 2nd circuit (internal woofers in "double cavity")
2nd order low pass
RLC networks to linearize impedance


I wish KEF published the frequency response of their drivers, I could simulate the circuit in VituixCAD. Following your idea, I went ahead and I've done the exercise with the Thiele/small parameters of each driver (except for the tweeter, for which I found no information online, so I used the tweeter of the 104/2 just to have an idea), and found out that if you remove all the compensations, you can almost halve the number of components. But without real response data, it's pretty pointless and it also means it's a completely new crossover. I wonder if KEF used to design and simulate their crossovers on computer at that time (1989), or if they simply designed them on paper after measurement., which would explain all the compensation subcircuits.

(btw, these speakers are a new acquisition for me)

edit: attached the simulation
Attached Images
File Type: gif circuit simplifiť.GIF (29.5 KB, 103 views)
File Type: gif circuit simplifiť2.GIF (36.2 KB, 95 views)
File Type: gif circuit simplifiť3.GIF (239.6 KB, 96 views)
File Type: gif circuit simplifiť4.GIF (126.3 KB, 96 views)

Last edited by lolilol1975; 20th September 2019 at 06:55 PM.
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Old 20th September 2019, 07:09 PM   #18
Xoc1 is offline Xoc1  United Kingdom
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I bought a cheap capacitance / inductance meter and ESR meter on ebay and had some capacitors precision measured as a reference. For the record the capacitance meter was out by about 7% and the inductance was about 1% but once known was easy to compensate for.
I have used them to rebuild crossovers for KEF Concertos and Tannoy monitor Golds.
I found that some of the old Elcap electrolytic capacitors in the KEF held their values but had quite a high ESR value, while others were massively dried out and not doing much at all. The replacement Alcap electrolytics have a lower ESR value but of course I have no idea what the original ESR values would have been when the crossover was new. Plastic caps have a very low ESR and this can cause problems . A plastic cap used in a low pass filter after an inductor can cause a resonant peak and need a small resistance in series with the capacitor to avoid the worse effects.
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Old 20th September 2019, 07:09 PM   #19
Galu is offline Galu  Scotland
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Quote:
Originally Posted by lolilol1975 View Post
Amortized Band cut ( <-- no idea why this is necessary )
Ha! Our posts obviously crossed!

The add-on circuits are basically to smooth the impedance of the bass drivers and to eliminate the midrange and tweeter resonances where they occur at specific frequencies.

The meaning of 'amortie' is 'damped'. The parallel LCR circuit is often called a contour circuit. It's purpose is to shape the frequency response of the driver, depressing, or damping, its output over a specific band of frequencies.
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Old 20th September 2019, 07:25 PM   #20
lolilol1975 is offline lolilol1975
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Originally Posted by Xoc1 View Post
I bought a cheap capacitance / inductance meter and ESR meter on ebay and had some capacitors precision measured as a reference. For the record the capacitance meter was out by about 7% and the inductance was about 1% but once known was easy to compensate for.
I have used them to rebuild crossovers for KEF Concertos and Tannoy monitor Golds.
I found that some of the old Elcap electrolytic capacitors in the KEF held their values but had quite a high ESR value, while others were massively dried out and not doing much at all. The replacement Alcap electrolytics have a lower ESR value but of course I have no idea what the original ESR values would have been when the crossover was new. Plastic caps have a very low ESR and this can cause problems . A plastic cap used in a low pass filter after an inductor can cause a resonant peak and need a small resistance in series with the capacitor to avoid the worse effects.
My crossovers have shiny Alcap and KEF branded caps. I'm wondering if they have been recapped already, in which case recapping a second time likely will not benefit at all.
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File Type: jpg IMG_20190920_212602.jpg (439.7 KB, 44 views)

Last edited by lolilol1975; 20th September 2019 at 07:28 PM.
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