Lsim 705 crossover schematic/help?

burialcloud

I have two Lsim 705’s with crossover damage from shipping. On one just the 75 uf cap broke free (as pictured). On the other (not pictured) this copper coil (circled) broke free and is semi unraveled. These aren’t covered by warranty.

Can someone provide me with what that is so I can replace it? Im used to old guitar amps and I’m lost here.
Also can anyone point me to a good source for a decent aftermarket 75uf. Doesn’t seem like a very readily available cap. Actually I’m not sure where to find either part.

Thanks for to any help you can offer.

F1nut

You can search Mouser or Digi-Key for the cap, but that spec was likely custom made just for Polk by some Chinese firm. Unless you can measure the good inductor, good luck. My advice, buy a new crossover from Polk, then swap the parts you require off of it.

VR3

You can shoe horn this guy on there, just keep it away from resistors

https://www.partsconnexion.com/SOLEN-51541_ss43616.html

burialcloud

So for the cap these are the two options I found through mouser, couldn’t find anywhere else with close to the right spec. Does the voltage matter? I know in guitar amps you can go up in voltage with zero issues.
The original was 75 uf 150v

Mouser has this cheap “United chemi-con” brand: 75 uf 160v
https://www.mouser.com/ProductDetail/United-Chemi-Con/EGXF161ELL750MK20S/?qs=8BXZADTIn4FjcY7UHntmZQ==

Or there is also this MUCH more expensive sprague which also has much higher voltage: 75 uf and 450v
https://www.mouser.com/ProductDetail/Vishay-Sprague/39D756F450JT6/?qs=czXXJdXbvZsUwEkO3ToQ3g==

It’s axial rather than radial but I could make it fit as there is plenty of extra space if the sound would benefit from the more expensive caps. The only other sprague in 75uf is only 75v which I’m guessing won’t work.

Obviously I will replace both so they match.

The weird thing about the inductor is they still function/work. I removed the other crossover today (pictured below) and this crossover unit was actually still working ok despite two inductors coming loose and one unraveling a little bit. I’m not really familiar with an inductors function or tolerance. Can I simply take them off the board, carefully rewrap the coil, secure it with new plastic and/or shrink tube and then re attach an zip tie?

Both that came loose have 5.0 mH printed beneath them. This board seems to have each parts measurement printed beneath it which is nice.




I did find these on parts express. Obviously a little different footprint but there is plenty of space to mount. Thoughts?

https://www.parts-express.com/erse-50mh-18-awg-i-core-inductor-crossover-coil--266-568?gclid=CjwKCAiA8ov_BRAoEiwAOZogwYvD103EyimLAQRKGEe444_mBwVAO66GKgYQqg7jjPty2gN6dWQz0RoCyakQAvD_BwE


Thanks for being patient with me!

VR3

You need a 75uf electrolytic

Radial configuration for ease of mount
Axial is side by side

And it needs to be bipolar

I searched mouser earlier snd they have no such monster, atleast any that states bipolar in the specs that the filter uses

I would remount the inductors

burialcloud

Hey! I was hoping you might chime in! I read through your post about doing a whole rebuild/upgrade on these.

Super appreciate the link to the cap! I’ll go with that and make sure I shrink tube around any leads and avoid resistor contact.

Awesome that the inductors should be fine. So was what I laid out sufficient for how to go about that?

How did your upgraded versions turn out?

burialcloud

While I’m at it is there any other caps or parts I could easily swap to make them better?

VR3

If you are rebuilding them then i would go with clarity cap.

The inductors are pretty durable and can be measured easily with the right equipment. It is important to match the MH/DCR ratings so you do not change the voicing.

I have never modded the 705, but the 703 is a very complex crossover with alot of parts. They will not fit back in the enclosure when you are done!

I can say the modded 703 were far superior to stock in almost every way.

burialcloud

I think I might be a bit confused. Were you saying the link you posted to the solen 75 uf 400v cap is an ok replacement for the 75 uf’s I need to replace? The ones that need replaced are marked 75 uf 150v bp

I’m just confused because the solen’s you linked aren’t electrolytic, and I’m not sure if those are bipolar which you mentioned they should be both those things in your follow up.

If those will work I’ll go ahead and order them but I’m a bit confused. Sorry!

VR3

Yes the solen will work, they are a film cap which is nicer than an electrolytic and is bipolar

burialcloud

Awesome! Sorry for my confusion. I’ll order them ASAP.
One last question. On the inductors, would plain old rubber-ey shrink wrap be ok to use on the outside or should I find some sort of shrink plastic?

Thanks for all your help. So pumped to hear these speakers.

VR3

You could use heat shrink or electrical tape

mm840lsi15

While the crossover board is on your desk, swapping those MTP 7.5uf and 2.7uf caps with proper Jantzen 400v polypropylenes might be a good idea. They are cheap, will fit perfectly and it's going to be an easy way to make your highs sound a little better

mm840lsi15

Would you kindly take nice pictures of the crossover from both sides please? Including the LF section. I would happily draw a nice schematic for us all to use.

Concerning that 24.?uf capacitor, it would also be easy and nice to replace it with proper polypropylene.

Can't see nicely from here, but I assume that moving all the resistors to the other side of the capacitor board would allow going full-polypropylene. I've done that with my LSiM703 and it worked out beautifully.

burialcloud

Sure can. I currently have a low frequency removed too. So I’ll do both. Give me about an hour.
And yea if you were to move resistors to the back you could just get longer screws and maybe some plastic tube/standoffs to allow for internal mounting still. I believe there would be enough space.

burialcloud

Hope this works. Should I ideally replace the ones marked MPT and MET as well or just the radials? The largest of those has glue and a zip tie covering it but I think it’s MPT 240J 100v. In case ya can read my crappy writing.
What brand would you guys go with?

burialcloud

Also, if anyone can point me to what brand, and perhaps a place where I can purchase them all at once that’d be awesome. I could only find the 75 uf in Solen (parts connexion) or Dayton (parts express) stateside. Seems like 75 uf is a surprisingly hard one to find. I found clarity but they’re outta England. I don’t wanna go crazy expensive and the shipping cost combined makes that a prohibitive option for me. I read some discussions back and forth on Dayton and Solen but I have no idea. This is all new to me.

I held off on ordering the Solen in case there is a place I can get them all at the same time to save on some shipping costs.

mm840lsi15

Cheers, chap. I'll try putting together the schematic today.

As for the caps, please note that combining caps of different capacitance is perfectly fine. Moreover, it is preferable to combine caps of different capacitance over using one capacitor, so all you need now is to try finding, for example, a nice 56uf 100v electrolytic (yes, 100v and yes electrolytic (when combined with polypropylenes) would be alright) Mundorf AC RAW cap and add Jatzen 15uf 400v and Jantzen 4uf 400v to it. By Jantzen I mean any cheap and good brand of polypropylenes. Lower frequencies allow using electrolytic caps so while keeping the HF and MF fully polypropylene, you may easily combine electrolytic and polypropylene capacitors for the lows. I try to stick with at least 25% polypropylene capacitance with my lows, if there's sufficient space.

Concerning space, space if everything, space is where those airwaves travel, so try keeping the crossover as compact as possible.

Concerning moving the resistors to the other side of the board - it's easy and won't cause any difficulties with spacing as the tube standoffs are longer that the height of the resistors. At least that's what I did with my LSiM703 crossovers and everything fit perfectly fine.



Moving the resistors on the back side of the boards frees up some space for proper polypropylenes (if you choose to go for board mounting like I did here). Please nevermind the amount of glue that I had to use.



Ah, forgot to add another idea for you. While your beautiful 705s are open, why don't you treat the insides of the cabinet with felt? Almost always a good idea, helps suppressing those ugly resonances. Troels Gravesen has a nice guide on this matter here: http://www.troelsgravesen.dk/cabinet-damping.htm

Your 705s are beautiful speakers and you'll do great, just double check everything and go one step at a time.

F1nut

Moreover, it is preferable to combine caps of different capacitance over using one capacitor

WRONG!!!

F1nut

Moving the resistors on the back side of the boards

You should have upgraded those crappy block resistors while you were at it.

F1nut

why don't you treat the insides of the cabinet with felt? Almost always a good idea

One can kill the sound very easily doing that. Polk filled the cabinets with just the right amount of poly fill to begin with.

VR3

Agreed there, strategically placed strips are the best route with padding versus the whole enclosure

mm840lsi15

F1nut wrote: »

Moreover, it is preferable to combine caps of different capacitance over using one capacitor

WRONG!!!

Elaborate please.

F1nut wrote: »

Moving the resistors on the back side of the boards

You should have upgraded those crappy block resistors while you were at it.

Didn't have those at hand, so good for now. Can be easily replaced later without having to disassemble the whole speaker.

F1nut wrote: »

why don't you treat the insides of the cabinet with felt? Almost always a good idea

One can kill the sound very easily doing that. Polk filled the cabinets with just the right amount of poly fill to begin with.

Right. That's why the treatment should be careful and the pads (and the crossover itself) should not eat up all the space inside.