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Speakerlab S7s Rebuild and Modding (Ribbon Tweeter Model)

3 weeks ago I ordered some Jantzen ribbon foil coils tor the woofer section of the crossover. The goal here is not louder bass but to see if the much nicer sound that was realized by using the ribbon foil coils in the other sections will translate into nicer bass. I tried to match the DCR as closely as possible but they are still 0.79 ohms as compared to 0.82 oms, so, 0.03 ohms less DCR. In this case I also ordered a complete set of Jantzen Crosscaps to go with the coils as well as Mills resistors. So these will be completely new boards and if the results prove to be much more sensitivity in the woofers I can simply swap the entire old boards back in. So, it's something like a €200 experiment that may or may not prove out.

The caps and resistors have arrived but I'm still waiting on the coils.

Also, I'm a little tired of dealing with wood screws when removing one of these boards to work on them. So I bought some little brass press nuts to insert into the backboard of the enclosure, as well as some M4 threaded brass rod and brass M4 nuts and plastic spacers. I'll cut some short lengths of threaded rod and end up with studs in the enclosure for mounting the boards and I can just slip them on and snug them down with nuts. Photos to follow when I get that mod done.

Cheers,
James
 
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So I have been learning about Shelving Filters, specifically a low shelf cut filter.

This came about when I was chatting with morfeora about crossovers and our speakers, and how I still have this annoying peak at the low end of the mid driver. It's something that I have been fighting to tame with mixed results. The discussion led to the benefits of externally mounted crossovers and then to his Canton CT 90's and their crossover schematics.

Something that I had noted in the past but never explored was that Canton had placed a resistor in parallel with the series cap in the mid section of the CT 90. Rodolfo has been exploring active crossovers lately and was able to explain what a shelf filter was and that that was what I saw in that mid section.It's good to have friends to learn from and share this stuff with!

Screenshot_Canton CT 90_3.png
R2 in the above schematic.

So all of this got me a bit excited and led to exploring in Xsim what it might be able to do for me.

Cheers,
James
 
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Xsim showed me that if I removed the 2x 1ohm series resistors that I had installed in the mid section and added a 27ohm resistor in parallel to the series caps it would knock down the low end peak on the mid by a couple of db.

Screenshot_Speakerlab S7s_05a2.jpg
Comparing this to the screenshot back in post# 430 shows a bit less of a low end hump on the mid. It looked promising and I happened to have a couple of 27ohm Mills resistors on hand so yesterday I pulled the mid boards and did the mod.

Cheers,
James
 
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The pair of 1ohm resistors has been replaced with a length of 1.5mm² wire and the 27ohm resistor added to the cap stack.

4 CD's later I am quite happy with this! The difference is a bit subtle but the bit of boomyness that I have been hearing is finally tamed and the speakers sound more balanced now. I'm loving that at 64 years old there are so many new (to me) things to be learned.

Cheers,
James
 
One thing that I have wanted to do for a long time was to make a better way of mounting the boards in the crossover box. Something that would make it easier to quickly remove the boards for modding.

To make that work I found some brass press nut inserts @ amazon. They are threaded for M4 screws and have an OD of 5mm.
Along with them I bought a 500mm piece of brass M4 threaded rod. The rod was cut into 24 pieces 19.5mm long and then the end threads were filed smooth at an angle. That ate up a bit of time.
M4 brass nuts were ordered and I used a 20mm and 4mm hole stamper to make some rubber cushion washers.

With that everything was ready to mount the boards.

DSC07485.JPG DSC07486.JPG DSC07487.JPG DSC07490.JPG DSC07503.JPG

The press nuts were tapped in place in 5mm holes and the studs screwed in. A pair of nuts were double-nutted on the studs and used to tighten the studs until they bottomed out, expanding the inserts and fixing them in place.

Cheers,
James
 
A rubber cushion washer was pushed down on each stud. After the boards were mounted a second rubber washer and brass nut finished the new board installation.

DSC07505.JPG DSC07496.JPG

Cheers,
James
 
Then the new woofer crossover boards were finally mounted.

DSC07497.JPG DSC07498.JPG DSC07499.JPG

A few notes concerning these boards.

There are very few differences between these boards and the 1st generation "new" crossovers in terms of absolute values. But they are closer to the original component values and layout now.
I returned the Zobel to 2 equal caps @33µF each, along with 2x 8ohm/10w Mills resistors.
Rather than a single 56µF cap for the parallel position I used a 22µf and 33µF, as in the original Speakerlab crossover. I threw in a 0.22µF bypass cap because they were laying around and well, because I felt like it.
The coil is 3.5mH rather than 3.58mH.

Because these boards are pretty much a final configuration I built them from the start for the connection wires to be soldered in place rather than using the clamps that I used for the tweeter and mid boards.

Early on I had the brilliant idea to make copper buss bars to connect everything. So I ordered some 0.6mm copper sheet to do that with. And a bench-top sheet metal bender to form some L-shaped parts. Well, that was stupid. When I made a test piece and tried to solder a piece of wire to it it was an epic fail. The sheet copper shed and spread the heat so quickly that even with my largest chisel-tip for the iron, along with paste flux and 400°c, you can forget about soldering a bunch of components to that.

So Plan-B was using some 2.5mm² copper wire formed and mounted to the boards to use as busses to connect everything. That at least worked very well and saved me from having to buy a bunch of the brass soldering stand-offs that I used the first time around.

Also, after assembling everything I applied a liberal amount of fingernail polish to the screws to lock them in place. In this case, green, borrowed from one of my daughters.

Cheers,
James
 
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So this is interesting.

For the record I did not expect any magical changes to the speakers with this mod. What I had hoped for is some cleaner bass from the use of the ribbon coils. Actually, I had no idea what the result would be, I was just hoping for something that I could claim to justify the funds expended.

What I got is interesting. Deep bass does not seem to be substantially different, at least not from the small amount of listening since the change. What has changed is that vocals are more coherent and understandable (especially when the vocals are low or the singer has a low voice), guitars are sweeter, and bass guitars have more twang. Soundstage is a bit more coherent and improved, as well as depth.

I'm actually quite happy with this development.

Cheers,
James
 
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OK, I rebuilt the tweeter boards to the same finished level as the woofer boards with the new Z-Silver and True-Copper caps. The ribbon coils and CDE 0.01µF caps were kept and the new caps have the same values as the last set, just a step up in quality. I just finished installing the boards a few minutes ago. As with the woofer boards I am satisfied enough that this will be the final configuration for the tweeters that the clamping blocks for the leads were left out and the leads are now directly soldered in place.

I'm going to wait a few hours for our apartment to cool down a bit before turning on the amp for the first listening session.

Cheers,
James
 
So here we are almost 3 years later. I took a long break from AK and am only now getting to a last few updates here.

Not only was I not finished but it became clear shortly after that last post in June of '21that I had made some mistakes, one quite serious.

First, I had not only not quite understood but also ignored the good advice of zaibatsu and managed to build a reverb unit out of the tweeter section.
zaibatsu had previously warned me that low impedance caps coupled with the low DCR coil risked creating a "tank circuit". And that is exactly what happened.

During that first listening session back in '21 it was very quickly clear that something was not right but it took me a while to figure out what. Everything sounded warbled and my amp got so hot that it shut down. Lucky for be it didn't burn up.
It took me a good bit of time to realize that I was listening to severe oscillation, my first time experiencing that. From there at least it wasn't to difficult to figure out what to do.

I first added a 0.47 ohm resistor in series with the coil and that helped considerably but didn't quite completely clean up the sound. Going with a 0.56 ohm resistor brought things back to normal but in the end just to be sure I went with a 0.68 ohm.

It was a very interesting learning experience that I never want to repeat.

Cheers,
James
 
My second basic mistake was adding all of those bypass caps.
Fellow member F1nut has posted a number of times about the potential consequences of using bypass caps, describing the results as sound artifacts.

This is another case of me not really understand what was being said but over time I realized that there were still sound problems with my speakers. I would use the analogy of taking a high res photo and slicing it into horizontal strips and re-assembling them all slightly skewed. Like there were conflicting out of phase images in the sound. It just didn't sound right. "it speaketh in Voices".

I ended up removing all bypass caps, not just in my speakers but everywhere, amps, CDP too. Then decided to just go with higher quality single caps (or matched pairs to reach a value).

In the tweeter section I stayed with the Jantzen Silver Z-Cap but made a small adjustment, going from 4µF total to 3.6µF, slightly raising the cutoff point.

DSC07614.JPG

Cheers,
James
 
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In the midrange section I went with some new Jantzen Z-Standard caps but stayed with the total values as before. I did do some more tweaking with the L-pad, ending with about 3.1db total attenuation on the mid. I also added a step filter on the lower end, a 27 ohm resistor in parallel with the cap.

DSC07615a.jpgDSC07616a.jpgDSC07617a.jpg

Cheers,
James
 
All of the above stuff was done during the summer of '21.

The result was finally reaching the point of total satisfaction with the speakers, and it only took me 9 years. :biggrin:
DSC07613a.jpg

Since that time all improvements to the sound of the speakers were done in the rest of the system. I'm getting some very balanced, very clean and clear sound.

Cheers,
James
 
One of the simplest and surprising things that I did to improve the overall sound quality of the entire system was adding 2 power conditioners last summer. 2 units because that lets me divide the 2-channel and 9.2-channel systems into 4 switchable banks.

These are Pavilens P20 EU units. I mainly bought them for the switching ability and was completely unprepared for the idea that the system instantly sounded overall cleaner, clearer, more precise.

I have read AK members thoughts on this and to be honest never really gave it much credit. I was completely wrong. This was in every way worth the total of €220 that I spent and I can highly recommend doing this.

IMG_20230819_185939_854.jpgIMG_20230819_185948_513.jpg

Cheers,
James
 
Lastly, the next major improvement was moving to monoblocks.
At the moment I am using 4 Marantz MA500 125wpc amps in bridged pairs. That is a temp solution while I get a pair of Denon POA 6600 250wpc amps repaired.

But the effect is interesting, and it is very pleasing that the speakers respond to the improvements very nicely, they just sound better and better.

IMG_20231204_152111_889a.jpg

So that's it. I really am done and feel that there is nothing left to explore with these speakers except better amplification and enjoying the music.
It has been an interesting journey.

Cheers,
James
 
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