Optimus LX-4 Black Dahlia mod issue - bypass cap breaks tweeter?

[kdawg123]

I have a pair of Optimus LX-4s that I'm modding based on the Black Dahlia mod (see details here).

One of the mods is adding a 0.1uf bypass cap in parallel with the existing cap. When I added the bypass cap, the tweeter stopped working. The tweeter started working again after I removed the bypass cap and plugged the speaker in. I'm pretty new to this, so it's possible I didn't solder the bypass cap on correctly. I used a Dayton Audio 0.1uF polypropylene bypass cap from parts express, which seems it's the same spec as what's recommended in the mod.

I've included some pictures of the bypass cap. Any ideas on what I'm missing here?

 

[sregor]

Pretty straight forward mod - I would guess you have a bad (shorted?) capacitor. I'm guessing you got two caps - did you try the other cap? Parts Express customer service is very very good.

 

[kdawg123]

Pretty straight forward mod - I would guess you have a bad (shorted?) capacitor. I'm guessing you got two caps - did you try the other cap? Parts Express customer service is very very good.

I didn't think of that. Just tried the other capacitor though and had the same issue. Scratching my head...

 

[sregor]

I can't think of anything that makes sense. Do you have clip leads (wires with alligator clips or other clips.) Only thing I can think of is something is being pushed out of position, or maybe sticking into one of the caps and making an inadvertent short? Good luck with it.

 

[Lavane]

Are you sure its a .1uf? Those Dayton caps look kinda big for a .1uf cap.
Could they acually be something like 1uf, or bigger?
I can't see how such a low value cap would kill the tweeter.

 

[kdawg123]

I can't think of anything that makes sense. Do you have clip leads (wires with alligator clips or other clips.) Only thing I can think of is something is being pushed out of position, or maybe sticking into one of the caps and making an inadvertent short? Good luck with it.

Thanks for the ideas...I'll test some more tomorrow to see if something is pushing on it, but it doesn't seem like it. I probably have enough room to visually inspect while having everything plugged in.
Are you talking at the terminal cup or woofer? They are spring type at the terminal cup and the tabs that get slotted over at the woofer

Are you sure its a .1uf? Those Dayton caps look kinda big for a .1uf cap.
Could they acually be something like 1uf, or bigger?
I can't see how such a low value cap would kill the tweeter.

Just doubled checked. The print says its a 0.1uf cap

Brand shouldn't really matter right? And it wouldn't make a difference going lower voltage? I guess I could try a lower capacitance, but the 0.1uf bypass kills the tweeter entirely right now. You'd think it would still have some sound.

 

[Lavane]

Brand shouldn't matter. What is the purpose of this bypass cap?

 

[kdawg123]

Brand shouldn't matter. What is the purpose of this bypass cap?

TBH, not entirely sure of the purpose. I assume for similar reasons people normally add bypass caps. It was one of the recommended mods in the black dahlia tip.

I sorted it out though. The tweeter wasn't dead all the way, just extremely quiet. Turns out this was due to another one of the mods, adding a piece of acoustic foam to the cabinet. Maybe the piece I added was too large, but it the added acoustic foam with the batt already in the cabinet totally deadened the cabinet. After removing the batting, the sound went from muffled to clear again!

Listening between the modded vs unmodded, it felt like the mods made the sound a little more even, but as a result possibly reduced some detail that I liked. Maybe it was due to the air coil inductor being 14ga (all they had in stock) vs the recommended 19 or 20ga.

All in all, I'm not super impressed with the mods. It resulted in minor improvements. Still a great pair of speakers though!