JBL S38 crossover mod (1 Viewer)

[Mark Hedges]

Care to post all of the values of the components you found?

Sure. I found the following:

Caps:

4 µF (Tweeter)
15 µF (Mid)
60 µF (Woofer)
3 x 0.01 µF (bypass)

Resistors

2 x 10W 2.4 ohm
1 x 10W 4.7 ohm
1 x 5W 20 ohm
1 x 5W 3.6 ohm

I ordered the following (all from Partsexpress):

Solen 3.9 µF cap
Solen 15 µF cap
3 x Audiocap Theta .01 µF (for bypass caps)

2 x Mills 2.5 ohm 12W resistor
Mills 20 ohm 12W resistor
Mills 4.5 ohm 12W resistor
Mills 3.5 ohm 12W resistor

You can see that some of the resistor values are off by 0.1 ohm or so but I figure that shouldn't be a problem, considering that the cheap resistors I am replacing have fairly broad tolerances (+/- 10%, I believe).

Mark

 

[SteveLeach]

Thanks Mark,
If I have the time this weekend, I'll dig into one of my S38II's and see if I find the same thing.
I'm looking forward to your review of how the mod turns out.

 

[Mark Hedges]

Since I am already in it for $100+ I decided to go all out and ordered 62 µF Axon caps for the Woofers from Speaker City. I hope I will be able to fit them on the board!

Mark

 

[Chris Tsutsui]

Sorry I havn't chimed in for a while, thought this thread died.

There did appear to be a physical difference between the S38II and S38 Original. This was the Midrange and most definitely the Port.

From what I remember, the flared port design the S38 original had used Bose patented technology in which a lawsuit made JBL have to change their ports to a different kind of flare and thus update them to S38ii.

The caps I got were too large, and sort of "hang off" the PCB bread board for the crossover. I did however screw the board down secure so that thing doesn't come loose and made sure my solder joints were strong.

Hopefully you will be successful with the S38ii mods like I was. As long as the component numbers are right and you didn't play any guessing games by changing the inductors then I think it'll be fine.

The capacitors are little guys that don't need to be charged, nor did I have to discharge them before pulling them out. On my S38s I think I had to use a "star" type torx screw driver. Either that it was a hex.

I got all my parts from Parts Express including the Dayton Film/Foil Bypass Caps.

Oh.. If you got high quality caps then you don't even need the bypass caps. Bypass caps are like a trick to improve sound quality by using a high quality small cap, with a lesser quality big cap.

 

[Mark Hedges]

I just had to use normal hex keys to open my S38's. I don't think the front panel comes off - I just worked thru the woofer hole (which is big enough).

I am not changing any inductors.

Chris - Did you do any work on the case itself? Polyfill, stiffener spray, etc?

Mark

 

[SteveLeach]

Well, I got paged last night and it was one of those start a process and wait kind of deals. So while I was waiting, I took a look inside one of my S38ii's (S/N HA0108-26565). I found the same components as you did Mark.

Caps:
4 µF (Tweeter)
15 µF (Mid)
60 µF (Woofer)
3 x 0.01 µF (bypass)

Resistors:
2 x 10W 2.4 ohm
1 x 10W 4.7 ohm
1 x 5W 20 ohm
1 x 5W 3.6 ohm

 

[John Tami]

Well I have an extra S26II....maybe when I can clear the Bench I can investigate it a bit. Thanks for all the info! That will help.

Chris! You live about 10 minutes from me! (I'm in MV) Always cool to find another slave to HT close by!

 

[Chu Gai]

On a slightly different note, I recall a website where someone had done mods on the JBL's (don't recall the model #) and had included some FR measurements. The gentleman also was involved in making either speaker boxes or kits. Would any of you happen to recall such a website and if so, post the link? Thanks!

 

[Mark Hedges]

I finished the mods over the weekend and reassembled the speakers last night. Everything went smoothly except for installing the deflex pads into the midrange enclosure. I had a hell of a time getting glue to stick to them and I still don't think they are rock-solid but I had to wrap this project up.

I haven't had a chance to listen to them much. Give me a week or so to break in the new caps and listen to a bunch of different stuff and then I will post my thoughts on what improvements I hear.

Mark

 

[SteveLeach]

Mark - Did you do any other mods to the cabinets besides the deflex pads? You mentioned above that you might "spray the case with stiffener". Did you do this? What product did you use? For the deflex pad, was it from parts express? Did you cover the entire back of the speaker or just the spot behind the woofer?

This past weekend I opened up two of my 38ii's and stuffed each one with half of a polyfil pillow. That's the only mod I've done so far, but I was surprised at how much it cleaned up the overall sound of these two when doing AB comparisons with an un moded pair.

 

[Mark Hedges]

I sprayed the inside with Cascade Quiete Kote VB-1S. But if I had to do it again I would probably try to find it in a brush-on formulation because it was impossible to get to all the surfaces on the inside of the speaker with a spray can.

The deflex pads were from parts express. I used the 5" pad behind the mids and the 9" pad behind the woofers. Right now there is no other damping material inside my speakers (no polyfil, etc.) From what I have read it seems that they recommend using the deflex pads by themselves without any polyfill or anything.

 

[SteveLeach]

Mark - Did you use 1 spray can of Quiet Kote per box? Also I see that Quiet Kote is solvent-based. How long did you let the speaker boxes stand before re-installing the drivers?

 

[Mark Hedges]

I used 1 can for both speakers, but it would probably be better to use 1 can per speaker and put on a couple of coats.

I waited 4 days to re-install the drivers but that was because I had so many problems with the deflex pads. I think 2 days would be fine, especially if you live in a warmer clime than upstate NY.

 

[SteveLeach]

Mark - What did you use as an adhesive to hold the deflex pads in place?

 

[Mark Hedges]

I used various forms of contact adhesive. It worked fine on the large pad behind the woofer but I had trouble with the smaller one behind the mid. For some reason the adhesive just didn't want to stick to the smaller pads.

I also touched it up with gelled super glue, which seemed to hold well.

Mark

 

[Mark Hedges]

Just for an update if anyone is interested -

Over the weekend I took the speakers apart one last time to solder all the spade fittings (they were fitting pretty loose from being disconnected so many times). I also took a piece of 1 1/4" dowel rod and glued it inside between the top and bottom panels of the cabinet. This seems to have made the cabinet much stiffer, as judged by tapping my nuckles on it. I also snipped off all the plastic in front of the tweeter.

Unfortunatly during reassembly I took a page from Chris' book and ruined one of the tweeters. A screw got away from me and slid toward the tweeter and the tweeters magnet did the rest. I am only out $29 shipped for a new tweeter from Harman but it will be another 2 weeks untill I get it.

I will say that I watched Kill Bill Vol.1 on Friday (before I did these latest & final mods) and the sound was incredible. The gunshot at the beginning made me jump out of my seat and the motorcycles at the end had me looking out the window to see if there was a motorcycle outside!

Mark

 

[SteveLeach]

Hey, sorry to hear about your tweeter woes... If all goes well, I'll be ordering the parts for the mod shortly. What was the total cost per speaker of your mods?

 

[Mark Hedges]

Total cost came to about $100 per speaker (including shipping & handing but excluding the new tweeter).

I figure crossover parts were about $60 per speaker and cabinet parts (deflex pads etc.) were about $40.

Mark

 

[Mark Hedges]

Now that I have listened to them some more I feel able to make some more comments.

In short, I am quite pleased with the results of this mod. I would say this is probably the most signifigant upgrade I have yet made to my system. Vocals are tighter, highs are less fatiguing, and instruments seem to have more presence.

Of course the problem is that I am comparing based on memory, which isn't the most accurate method. I wish I had a stock pair of S38II's around to A/B but I do not.

If I were to do it over again I probably would not bother with the deflex pads (at least for the woofer), and maybe not change the 60 µF cap on the woofer. The bass seems maybe a little tighter, but I do not think the results are worth the cost of those parts.

Mark

 

[SteveLeach]

Thanks for the update Mark,

I've received the parts I need to mod mine.

As I have 3 pair to do. I plan on leaving one pair stock, doing one pair with the deflex pad for the bass only, and the last pair with out any deflex pads.

My schedule is pretty full right now, but I'm hoping that I can get the time in the next week or so to get this done.