KLS 3--Radical re-design

[Guy Pettigrew]

You may remember a thread about upgrading the crossover components in my KLS 3s after Peter Comeau had replaced my piezo tweeters with SEAS millennium ones.

After the rebuild a friend of mine who has been designing and building 'speakers on an amateur basis for 40 or so years suggested trying out some modifications to the crossover circuit. Despite being a bit unsure I made some tentative changes. Seemed reasonable, as the crossover could easily be put back to its original spec. And if you never try, you never know! The result was the bass and mid sections of the crossover remained the same, but the tweeter section was reduced to just one 4.7uF capacitor in series with the drive unit.

And this is how it remained for a couple of years, other than rebuilding the mid range enclosure to ensure it was airtight.

Last Friday things changed hugely. My mate had persuaded me to become a bit more adventurous and had offered to come round to guide me in trying other ways of configuring the 'speakers.

We spent several hours trying all sorts of things. He had the easy job of making the suggestions. I had the hot and sweaty job (it was nearly 30C that day!) of crawling around behind the 'speakers to put components in and out of the circuit. Fortunately all the crossover components are on a board on the back of the cabinets.

The end result was almost entirely different from where we started. The tweeter still has the 4.7uF capacitor in series, but that's where the similarity ends.

Are you sitting down? The bass and mid drivers are now wired in series with no crossover components at all! This has significantly improved the bass control, the imaging, punch and timing of the KLS 3s.

It may be because the amps, WAD 300B PSEs, like the higher impedance presented to them. Or it may not! All I know is it sounds much, much better.

Guy

[Yellow]

Guy,
Interesting read. There are of course, several designs out there which do the same, but to get a 3-way to work with no x/o components in the LF & MF sections is odd. the main reason would be that the MF unit will go quite low before naturally rolling off - maybe down to 200Hz or so. Likewise the LF unit will be good up to 1kHz in terms of output, so what you may have done is to boost the 100-1.5kHz output quite substantially, as both units will be working in tandem. Whether it is all operating in phase remains to be seen.

Always worth trying these things out though. Leaving a cap (1st order) in series with the HF is an absolute MUST though, otherwise, it'll get cremated as you crank up the volume.

Regards,

Neil.

[Brian]

Originally Posted by Yellow

Guy,
Interesting read. There are of course, several designs out there which do the same, but to get a 3-way to work with no x/o components in the LF & MF sections is odd. the main reason would be that the MF unit will go quite low before naturally rolling off - maybe down to 200Hz or so. Likewise the LF unit will be good up to 1kHz in terms of output, so what you may have done is to boost the 100-1.5kHz output quite substantially, as both units will be working in tandem. Whether it is all operating in phase remains to be seen.

Always worth trying these things out though. Leaving a cap (1st order) in series with the HF is an absolute MUST though, otherwise, it'll get cremated as you crank up the volume.

Regards,

Neil.

I'm not at home so I can't get at the supplement, but from memory, in KLS3 MK1, the midrange rolls off naturally at ~100Hz due to the volume of the chamber wiith the bass filtered accordingly.

In KLS3 MK2, the bass unit is allowed to operate upto 400Hz with the midrange now filtered to cut it off, the version used by Guy is based on this arrangement, so basically I can't imagine how the speakers are working as described by Guy.

[Greg.]

Hi Brian,

Nice to see you on the forum after a long time. Email or PM me and let me know how things are.

Greg

[Butterfly_pete]

Hello all,
I was feeling in a playful mood, do I tried the "Guy" mod.
Initially the sound was OK, Just OK.
I lived with it for a while then put on "Close to the edge" by Yes.
Jon's voice is, now, a pain to hear.
I immediately got my old spares, Epos 11's just to be sure my amp wasn't playing up. No, its the KLS3's (Mk1).
I've played the album a couple of times with the Epos 11's and heard things I've never heard before.
Now I'm gonna replace the KLS3's X-over to the prefered values.
So moral of the story is, Try different speakers every now and again, some time to compare with.
Always try lots of different music when trialing speakers
And, always carry around with you a copy of "Close to the edge"

Greg, have you been playing around with the component values.
What's the latest recommended values and suppliers
Cheers
Pete

[Greg.]

Pete, my recollection is that although Guy reported satisfaction with last reported configuration of his KLS3, he had deviated from the build instructions in general. In particular his cabinets were over damped by a significant margin. His last crossover incorporated changes a Peter Comeau made to the whole crossover when he converted them to be used with the Seas Millennium tweeter. I have never heard this version and until I do (unlikely) I'll remain suspicious of it bringing any advantage.

My KLS3's remain in the original Mk1 guise using the Audax silk dome tweeter but I am now using the Mk2 crossover, adjusted for the original tweeter. See the FAQ for details. To me this is a more balanced and refined crossover (see Brian's post above) and I much prefer the resulting sound. I have not at any stage altered any crossover component values as, in my listening room, the original values work well. When I rebuilt the Mk1 crossover with boutique components, I did uprate the resistors to the next wattage value just to give them an easier time and hopefully protect from value drift that can comes with age and use. All electrolytic caps were changed to polypropylene.

Having listened to several different speakers up to the value of £40k, even if I could afford them, nothing has convinced me to change my KLS3's. They work so well in my system and I simply love them.

Hope that helps.

[Butterfly_pete]

Hello Greg,
Ive looked in the FAQ for KLS3 but got no articles.
What should I look for.
Cheers
Pete

[Butterfly_pete]

Hello again Greg,
I was looking at the top tab that said "FAQ" then in "Search word(s):" I put in KLS3, with the resulting "Sorry no matches", Silly me...
I just found in FAQ -Upgrades and Tweaks about upgrading a tweeter, is that the article you refered to?
I have the original Hi-Fi world supplament No9 August 1994 with the original componants.
I also have a copy of the KLS3 Mk1 at a later date (2004)
the componant values are different.
The first article has C1 is 4uF. in the second article C1 is 2uF, etc
Am I right in assuming you are using the values from the latter article?
Cheers
Pete

[Greg.]

Hi Pete,

Yes, the tweeter article in the FAQ 'Tweaks and Upgrades' section is the one, but be aware this relates specifically to use with the KLS3 Gold Mk2 crossover. The same tweeter is used in the Mk1 and the Mk1 crossover still applies unless you choose, as I would recommend, to upgrade to the Gold Mk2 version. This means incorporating the original Audax TW025M1 tweeter, using the modified circuit you have found in the FAQ.

Regarding the original Mk1 crossover circuit, I understand where your confusion lies. The circuit published in supplement 9, Aug 1994 was the one used with the prototype speaker build and was changed when the kit was released. This published circuit is completely wrong and should not be used. Because of interlectual property rights, I have asked Matthew if I can publish here the correct Mk1 circuit. This is what WAD should have done at the time as an addendum in the supplement. In the mean time I can confirm that C1 should be 2uF and not 4uF. Furthermore, referring to the published but wrong circuit, as shown, C1, C2a & 2b, R1, L1, L2, are all wrong and in the correct circuit, a resistor is added in parallel across the +ive and -ive on the midrange driver.

In total, to the best of my knowledge, a total of five different crossover circuits exist for all the versions of KLS3. One is completely wrong, corrected by the unpublished Mk1 kit version. The next is for KLS3 Gold, another for Gold Mk2 and finally is the version Peter Comeau used with Guy's speaker when converting for use with the Seas Millennium tweeter.

I hope that helps for now. Hopefully Matthew will allow me to publish the corrected diagram in due course. I am also sending you a PM.

Greg