I have recently bought a pair from a kind gentleman who sent them to me their huge size notwithstanding. The original crossovers (schematics is somewhere on this site) were a bit tired sounding and gave too much mids for my taste. I researched the cornucopia of different filter networks for the combination of drivers which is huge (new “improved” Falcon and Wilmslow crossovers, old “improved” Falcon crossovers, the elusive Falcon “AusKEF” crossover (found only two blurry photos on the web, no circuit), Radford crossover, IMF crossover, Cambridge R50 crossover and more).
I did not want to spend much money on new crossovers and I wanted to keep the position of them on the front baffle – very handy for easy swapping of components. I did a lot of tests and finally settled for the circuit below. It incorporates the original aB circuit from the 104aB (not the “simplified” one which some of the Falcon crossovers use). The speakers sound fantastic now. I have a pair of KEF reference 105’s as a, well, reference. Strengths of the Concertos are a sweet, sweet midrange, a tuneful, deep and fast bass, and a treble that is never sharp. Imaging is very good (though not as spectacular as with the 105’s, but that would be hard to do).
I was even thinking of designing a circuit board to swap in the place of the old one, but I am short of time. I reused the original inductors apart from the one in the treble circuit, which needed a higher value. I turned the crossovers 180 degrees to accommodate the bigger components (there are also some elements on the solder side). I had to rotate the connector in order to do that. Now the Concertos are outstanding. They have this rare “rightness” about them. I tested them with my usual fleet of amps, among them a Kenwood KA-6000, Sansui TR-707, NAD 3140, Musical Fidelity B1, and Onix OA46 (all restored-recapped-upgraded).
See the circuit for the particular caps I used. The crossover is very sensitive of the type of cap. I tried various combinations (polyester, polypropylene, “raw” foil, “smooth” foil, aka LL, low loss). The caps in parallel to the drivers were – against some opinions I had found – MORE sensitive to the type and quality of the caps used there, particularly in the mid circuit. What is in the schematics now is what sounded most sensible after weeks of trials. I don’t have measurement equipment, but, as I said, the (serviced) served 105’s as a reference.
It was also VERY important to clean the connectors to the crossover, giving immediate audible results. I assume many reports of the Concertos performing sub-par have to do with dirty contacts here.
(PS Sorry, couldn't manage to upload the photo upright although it is taken and saved that way on my computer.)
I did not want to spend much money on new crossovers and I wanted to keep the position of them on the front baffle – very handy for easy swapping of components. I did a lot of tests and finally settled for the circuit below. It incorporates the original aB circuit from the 104aB (not the “simplified” one which some of the Falcon crossovers use). The speakers sound fantastic now. I have a pair of KEF reference 105’s as a, well, reference. Strengths of the Concertos are a sweet, sweet midrange, a tuneful, deep and fast bass, and a treble that is never sharp. Imaging is very good (though not as spectacular as with the 105’s, but that would be hard to do).
I was even thinking of designing a circuit board to swap in the place of the old one, but I am short of time. I reused the original inductors apart from the one in the treble circuit, which needed a higher value. I turned the crossovers 180 degrees to accommodate the bigger components (there are also some elements on the solder side). I had to rotate the connector in order to do that. Now the Concertos are outstanding. They have this rare “rightness” about them. I tested them with my usual fleet of amps, among them a Kenwood KA-6000, Sansui TR-707, NAD 3140, Musical Fidelity B1, and Onix OA46 (all restored-recapped-upgraded).
See the circuit for the particular caps I used. The crossover is very sensitive of the type of cap. I tried various combinations (polyester, polypropylene, “raw” foil, “smooth” foil, aka LL, low loss). The caps in parallel to the drivers were – against some opinions I had found – MORE sensitive to the type and quality of the caps used there, particularly in the mid circuit. What is in the schematics now is what sounded most sensible after weeks of trials. I don’t have measurement equipment, but, as I said, the (serviced) served 105’s as a reference.
It was also VERY important to clean the connectors to the crossover, giving immediate audible results. I assume many reports of the Concertos performing sub-par have to do with dirty contacts here.
(PS Sorry, couldn't manage to upload the photo upright although it is taken and saved that way on my computer.)
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That is very interesting.
I'm surprised to hear you found Concertos gave "too much mids", in my case I find them mid recessed (at lower mids). Mine are KefKit 3 (slightly smaller cabinets: 37,5 cm wide by 29,5 depth) with Falcon higher power crossovers No.33Mc (the old ones not the current ones with a red board) which I feel do not change the sonic signature of the originals. I'm listening them with a Kenwood KA7300 boosting bass two notches up at 400hz and cutting treble two notches at 3khz, this way it fills up the body/mids! Problem is they only sound right to me with an amp that allows that kind of tweaking so I thought about modifying crossovers, I posted here about it https://www.diyaudio.com/forums/analog-line-level/375737-modify-speakers-passive-crossovers-mimic-external-eq-curve-2.html
So the crossover circuit you're using is the original 104ab? I'm tempted now to try modify the original ones I have lying around to see the results... but then... you feel it does cut body/lower mids?
Thanks
I'm surprised to hear you found Concertos gave "too much mids", in my case I find them mid recessed (at lower mids). Mine are KefKit 3 (slightly smaller cabinets: 37,5 cm wide by 29,5 depth) with Falcon higher power crossovers No.33Mc (the old ones not the current ones with a red board) which I feel do not change the sonic signature of the originals. I'm listening them with a Kenwood KA7300 boosting bass two notches up at 400hz and cutting treble two notches at 3khz, this way it fills up the body/mids! Problem is they only sound right to me with an amp that allows that kind of tweaking so I thought about modifying crossovers, I posted here about it https://www.diyaudio.com/forums/analog-line-level/375737-modify-speakers-passive-crossovers-mimic-external-eq-curve-2.html
So the crossover circuit you're using is the original 104ab? I'm tempted now to try modify the original ones I have lying around to see the results... but then... you feel it does cut body/lower mids?
Thanks
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Hi Marintz,
thanks for adding this info. Very interesting, indeed. The improved Falcon crossovers in your Concertos actually do have the aB section (see the extra air core inductor on the board). EDIT: maybe not, after looking at your photo of the Xover it seems to me that the air core could also be in the mid section of the circuit. See post below.
As the crossovers are new-ish, they should not suffer from dried-out alcaps. I never heard those, so can't tell if Falcon got the balance right. They usually, but not always, do.
Re the "lower mids", I guess it all depends. Which frequency are you talking about? According to what you dial in on your amp those frequencies are probably handled by the woofer (don't know the crossover point of the 33Mc). As any room is different, the lack of lower mids-upper bass may also be a room effect on your side. The Concertos with "my" crossover version are rather warm below 400Hz, and are slightly more bassy than the 105's.
Another factor to consider is wear on the original B110s. Some sources suggest that they are all off-spec now due to ageing. I'd love to test a pair of new B110's from Falcon, but that's expensive.
What you describe may also be related to the amps you're using. To my experience many solid state amps sound thin in the frequency domain you're referring to. Particular if they're vintage and the caps now become old.
I also own the KA-7300. It's a lovely and very potent amp, but it became much better after I did some changes. Even recapped, but not upgraded, I found it sounding to thin without me dialling in more bass or using the loudness switch.
What other amps did you test the Concertos with? In my anecdotal experiments I they are really great with a (again, recapped-upgraded) Kenwood KA-6000. They are even too bassy with a Sansui TR-707. They are also quite lovely and very delicate sounding with an Onix OA-46.
What you could try is insert a parallel resistor in the mids section of the 33Mc network. See my schematics. This parallel R did a lot of things in my Xover, and I loved it. (It would be fantastic, by the way, if at that occasion you could draw the schematics of the crossover and make it accessible to the community here
.
Adding the 1Ohm had effects less audible in the mids, but more in the bass. So maybe that's something to experiment with. Using a polypropylene (with low ESR) in parallel with the mid driver had the opposite effect – it really unbalanced the sound.
I'm curious what your experiments will turn up!
thanks for adding this info. Very interesting, indeed. The improved Falcon crossovers in your Concertos actually do have the aB section (see the extra air core inductor on the board). EDIT: maybe not, after looking at your photo of the Xover it seems to me that the air core could also be in the mid section of the circuit. See post below.
As the crossovers are new-ish, they should not suffer from dried-out alcaps. I never heard those, so can't tell if Falcon got the balance right. They usually, but not always, do.
Re the "lower mids", I guess it all depends. Which frequency are you talking about? According to what you dial in on your amp those frequencies are probably handled by the woofer (don't know the crossover point of the 33Mc). As any room is different, the lack of lower mids-upper bass may also be a room effect on your side. The Concertos with "my" crossover version are rather warm below 400Hz, and are slightly more bassy than the 105's.
Another factor to consider is wear on the original B110s. Some sources suggest that they are all off-spec now due to ageing. I'd love to test a pair of new B110's from Falcon, but that's expensive.
What you describe may also be related to the amps you're using. To my experience many solid state amps sound thin in the frequency domain you're referring to. Particular if they're vintage and the caps now become old.
I also own the KA-7300. It's a lovely and very potent amp, but it became much better after I did some changes. Even recapped, but not upgraded, I found it sounding to thin without me dialling in more bass or using the loudness switch.
What other amps did you test the Concertos with? In my anecdotal experiments I they are really great with a (again, recapped-upgraded) Kenwood KA-6000. They are even too bassy with a Sansui TR-707. They are also quite lovely and very delicate sounding with an Onix OA-46.
What you could try is insert a parallel resistor in the mids section of the 33Mc network. See my schematics. This parallel R did a lot of things in my Xover, and I loved it. (It would be fantastic, by the way, if at that occasion you could draw the schematics of the crossover and make it accessible to the community here
. Adding the 1Ohm had effects less audible in the mids, but more in the bass. So maybe that's something to experiment with. Using a polypropylene (with low ESR) in parallel with the mid driver had the opposite effect – it really unbalanced the sound.
I'm curious what your experiments will turn up!
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I looked at your equalizer setting with which you attempted to undo the supposed frequency bending of the Concertos. There it's more in the mids region and not in the upper bass, true. I wonder if the air core inductor indeed is part of the tweeter section, or if it is not in the mid section, in order to give a steeper separation between mids and bass or tweeter. see edit in the previous post. So i would be really helpful if you could trace the circuit... then someone here could even simulate it.
As the with the original Xovers the speakers sounded to "middly", in my version I attenuated the mids by a 2.2Ohms resistor, instead of making the separation of a different order, and thus stronger, by introducing another inductor. The "middy-ness" of the Concertos has been discussed in the KEF vintage forum (Home Page hifiloudspeakers.info).
If you want to try out my Xover version: all the components fit on the original plug-in boards, although you'd need to rotate the boards and the plugs (easy) so that the components face outward. Some later Concertos already had the Xovers fitted that way. You can re-use all inductors from the original board and need to add one extra for the aB circuit.
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Some more thoughts. I tried to reconstruct the schematics.
Falcon uses a 60uF in the bass section, which to my ears does not sound right, as it gives a mid bass hump. Then they added (if I'm right) a third inductor in the mid section, like KEF did with its last iteration with the B139-B110-three way design, the CS7 (which uses the B110B and the T33A tweeter, so it is not sure if one could directly "translate" the mid and treble section of the Xover to the B110A and T27 combination, probably not.)
See the CS7 network for reference. Falcon might have overdone the low-mid pulldown with their version. Falcon also uses their "simplified" aB network, which to my eyes is just that, (too) simplified. See again the CS7 with the complex aB network.
Falcon uses a 60uF in the bass section, which to my ears does not sound right, as it gives a mid bass hump. Then they added (if I'm right) a third inductor in the mid section, like KEF did with its last iteration with the B139-B110-three way design, the CS7 (which uses the B110B and the T33A tweeter, so it is not sure if one could directly "translate" the mid and treble section of the Xover to the B110A and T27 combination, probably not.)
See the CS7 network for reference. Falcon might have overdone the low-mid pulldown with their version. Falcon also uses their "simplified" aB network, which to my eyes is just that, (too) simplified. See again the CS7 with the complex aB network.
Hello Eschenborn, thanks for the info!
My Kenwood is recapped just in part, control, phono and power supply boards... and not all caps in these boards. Power amp boards and big caps remain original. I tried the Concertos too with a Yamaha CA810 (not recapped) and a Yaqin mc13s (6CA7 tube amp) and the difference was subtle, I'm still not decided on which one I prefer, it varies... this is crazy! For a while I was liking more the Yaqin, now the Kenwood... but to get the Concertos to sound with the desired EQ trough the no tone controls Yaqin i'm using the Kenwood as preamp and feeding it into one of the Yaqin line inputs, maybe not the best way to do it, i wonder if sound gets degraded somehow... in any case it must be very subtle
When using the Yaqin with another speakers that needed no EQ to sound right to me I felt there was slightly deeper bass with the Yaqin but the kenwood felt a bit more airy, with maybe a bit more presence... but I'm talking from memory, this is a bit subjective
I'll try to get back again and read more throughly your posts, no time now
My Kenwood is recapped just in part, control, phono and power supply boards... and not all caps in these boards. Power amp boards and big caps remain original. I tried the Concertos too with a Yamaha CA810 (not recapped) and a Yaqin mc13s (6CA7 tube amp) and the difference was subtle, I'm still not decided on which one I prefer, it varies... this is crazy!
For a while I was liking more the Yaqin, now the Kenwood... but to get the Concertos to sound with the desired EQ trough the no tone controls Yaqin i'm using the Kenwood as preamp and feeding it into one of the Yaqin line inputs, maybe not the best way to do it, i wonder if sound gets degraded somehow... in any case it must be very subtleWhen using the Yaqin with another speakers that needed no EQ to sound right to me I felt there was slightly deeper bass with the Yaqin but the kenwood felt a bit more airy, with maybe a bit more presence... but I'm talking from memory, this is a bit subjective
I'll try to get back again and read more throughly your posts, no time now
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Thanks for the description, very interesting again. I never listened to your other two amps, but know that the Yamaha if recapped should be pretty good. And the Yaqin, as it is a tube amp, should match well with the Concertos, as they can transmit that sweetness. If it can deliver enough power, that is.
I've invested quite a bit work in my KA-7300 in order to understand why it did not sound really great even after a full recap. I found that the signal must go through a lot of switches in the pre-amp, and those get dirty. So these should all be cleaned (by disassembly and actually cleaning the contacts with a leather stick or so). Huge work.
In my amp, I have bridged all the switches after the first pre-amp differential directly into the power amp. Some previous owner had replaced the volume knob by a non-original one which he has then glued on the pot, so I can't disassemble the pre-amp and am unable to clean the switches... a true genius. I found that shorting out the switches worked wonders. I have still the loudness dial if I want more bass.
I also bridged the pre-out - main-in connectors with short RCA cables and set the switch to "separate", as this was oxidised as well. The amp also needs a new relay because of oxidised contacts... even if it still works. My experience is that dirty contacts degrade the sound. Cleaning all of them is often more work than a full recap, unfortunately.
I also changed the input cap to the power amp from the original 0.22 polyester to two 0.47 WIMA MKP4 polypropylenes in parallel. this was also pretty audible and helped a lot. I'm actually preferring the KA-7300 in this form over all other great amps I have collected over the years. I simply swap it back in all the time. But that's another thread
So all this might be helpful and could make you get rid of your frequency disbalance problems on the KA-7300 side... but the Falcon crossover might also simply be unbalanced. If you still have the original DN12 crossovers, and are in the mood for tinkering, you can relatively easily "mod" them to "my" version and hook them up in the speakers.
I've invested quite a bit work in my KA-7300 in order to understand why it did not sound really great even after a full recap. I found that the signal must go through a lot of switches in the pre-amp, and those get dirty. So these should all be cleaned (by disassembly and actually cleaning the contacts with a leather stick or so). Huge work.
In my amp, I have bridged all the switches after the first pre-amp differential directly into the power amp. Some previous owner had replaced the volume knob by a non-original one which he has then glued on the pot, so I can't disassemble the pre-amp and am unable to clean the switches... a true genius. I found that shorting out the switches worked wonders. I have still the loudness dial if I want more bass.
I also bridged the pre-out - main-in connectors with short RCA cables and set the switch to "separate", as this was oxidised as well. The amp also needs a new relay because of oxidised contacts... even if it still works. My experience is that dirty contacts degrade the sound. Cleaning all of them is often more work than a full recap, unfortunately.
I also changed the input cap to the power amp from the original 0.22 polyester to two 0.47 WIMA MKP4 polypropylenes in parallel. this was also pretty audible and helped a lot. I'm actually preferring the KA-7300 in this form over all other great amps I have collected over the years. I simply swap it back in all the time. But that's another thread
So all this might be helpful and could make you get rid of your frequency disbalance problems on the KA-7300 side... but the Falcon crossover might also simply be unbalanced. If you still have the original DN12 crossovers, and are in the mood for tinkering, you can relatively easily "mod" them to "my" version and hook them up in the speakers.
Thanks for the tips! I'm glad you find the schematics helpful
I also increased the input caps at power boards, IIRC from .47uf to 1.5uf. My kenwood used to lack bass on one channel and it seems it had to do with preamp switches or the pre out/main in rca, after some deoxit cleaning it's working apparently problem free. I don't intend to get rid of the preamp section as for now it's what's making the speakers sound right, without it sound is kind of thin... body is lacking at upper bass/lower mids and I don't think it's an amp issue.
I'll definitely try your crossover mods when time allows (i'll let you know) first with cheap components on one of the original boards, I'll leave the existing ones that are the same value, and if it does the trick i'll go serius and change everything but the inductors.
I also increased the input caps at power boards, IIRC from .47uf to 1.5uf. My kenwood used to lack bass on one channel and it seems it had to do with preamp switches or the pre out/main in rca, after some deoxit cleaning it's working apparently problem free. I don't intend to get rid of the preamp section as for now it's what's making the speakers sound right, without it sound is kind of thin... body is lacking at upper bass/lower mids and I don't think it's an amp issue.
I'll definitely try your crossover mods when time allows (i'll let you know) first with cheap components on one of the original boards, I'll leave the existing ones that are the same value, and if it does the trick i'll go serius and change everything
but the inductors.
An update about my experience with Falcon Concerto crossovers to make them justice. When I installed them some years ago I didn't notice much difference with the originals but maybe more refined high frequencies (they were fresh, brand new) BUT yesterday I compared them again and the difference after being used for a long time is very noticiable for the better 
... more solid sound, better bass, more body... Still for some reason (maybe my particular drivers) as discussed here I need some more tailoring to make my speakers sound as I want.
... more solid sound, better bass, more body... Still for some reason (maybe my particular drivers) as discussed here I need some more tailoring to make my speakers sound as I want.Hi, in my case i used AWG16 (1.29 mm.)
Another update, I tried Eschenborn schematic although in a test manner not with all exact values (30 instead of 33uf, 0.25 instead of 0.30mh) keeping most of the old caps and all inductors and I find it sweeter than the Falcon version, which I find more scooped... Escheborn's is easier on the ear, more pleasant, I think I'm going to get good parts and go ahead with it! Thanks Eschenborn !
The only thing is it's a bit hard to get all the parts on the Kef board. Still I'm missing some body, upper bass, lower mids. I was wondering if these changes will get me a bit closer without messing things up?:
-Lowering the value of the b139 inductor to about 4mh and cap to about 50-68uf
-Increasing the gauge of this inductor to about 1,4mm (16-14AWG)... although I see prices increase fast
Another update, I tried Eschenborn schematic although in a test manner not with all exact values (30 instead of 33uf, 0.25 instead of 0.30mh) keeping most of the old caps and all inductors and I find it sweeter than the Falcon version, which I find more scooped... Escheborn's is easier on the ear, more pleasant, I think I'm going to get good parts and go ahead with it! Thanks Eschenborn !
The only thing is it's a bit hard to get all the parts on the Kef board. Still I'm missing some body, upper bass, lower mids. I was wondering if these changes will get me a bit closer without messing things up?:-Lowering the value of the b139 inductor to about 4mh and cap to about 50-68uf
-Increasing the gauge of this inductor to about 1,4mm (16-14AWG)... although I see prices increase fast
ps: I‘d not cross over the woofer at a higher point as your suggestion would do. the B139 has some bad breakup modes rather early. KEF in their various iterations of the B139 three way made the separation between bass and mids always steeper. maybe a thicker inductor has an effect- but might not fit on the board.
the quality of the caps at their placed in the crossover is very important. try for the mid section a 30 or 33uF nee low loss or „plain foil“ cap. that has a big effect. otherwise you could experiment with low ohm parallel resistors in the bass section. I didn‘t as I found my version was ok as it was.
the quality of the caps at their placed in the crossover is very important. try for the mid section a 30 or 33uF nee low loss or „plain foil“ cap. that has a big effect. otherwise you could experiment with low ohm parallel resistors in the bass section. I didn‘t as I found my version was ok as it was.