Modding RT25i crossover ?

heiney9

I've decided to mod the x-overs in my wonderful sounding Polk RT25i's. I have been wanting to do this for awhile now.

For the tweeter section they use an 8uF electrolytic and a 1.0uF mylar in parallel and a 2 ohm resistor in series.

I am having a heck of a time finding a 9uF capacitor other than Sonicap Gen I which makes the exact value. I have done Sonicaps before several times, so I was looking for something different this time.

As always these are in rotation in a secondary rig (might make a 3rd rig one day) so they don't get a lot of use. The idea is to keep the costs down. I'd like to keep the entire project to about $50.

Resistors will be Mills 5 watt 2.0 and 3.5 ohm $6 each crossover
27uF Low pass cap will be Solen PB $11 each crossover

I have some options as far as caps for the tweeter.

1. 9uF Sonicap Gen I $19.01 each crossover (over budget)
2. 3.3uF & 5.6uF Mundorf M-Cap Evo $11.23 each crossover
3. 2.2uF & 6.8uF Mundorf M-Cap Evo $11.88 each crossover
4. same values as above Mundorf M-Cap Evo oil $20.20 each crossover (over budget)
5. same values as above Clarity Cap ESA $23.00 each crossover (over budget)
6. same values as above Clarity Cap PX $11.00 each crossover

I am open to other suggestions. I've never used Mundorf and I know some have and sware by them. I am a big fan of Clarity Caps and already use the PX series in my 5B's. This is where I'm leaning, but I can be convinced to go another route.

So let's discuss.

H9

heiney9

Now I remember why I hate doing crossover mods..................can't get ALL the stuff from one website....lol.

Madisound has 9.0uF PX and ESA Clarity Caps, but don't carry the 27uF Solen Cap (only 25uF cap). Other places have the 27uF Solen but don't carry a 9.0uF cap.

This means paying shipping twice.

Really irritating.

westmassguy

9uf Clarity PX for the Hi-Pass and 12uf + 15uf Clarity PX for the Lo-Pass. Little over budget, but much better than Solens.

lightman1

Where are you gonna mount the tube sockets?
I suggest on the top for heat dissipation.
Put up your dukes Brock!

Nightfall

lightman1 wrote: »

Where are you gonna mount the tube sockets?
I suggest on the top for heat dissipation.
Put up your dukes Brock!

Too much vibration to mount tubes directly in/on a pair of speakers, quit yer trolling!

lightman1

Never

F1nut

I LOVE Mundorf caps in electronics, but I've never used them in a crossover. That said, I think they'd be worth trying.

heiney9

Yeah, been wanting to try Mundorf's in something. The oil ones have me a bit intrigued. I need to pull the x-overs again and familiarize myself with the real estate available to make all this work.

Size does matter and I might be limited in that area as I'm not wanting to turn this into a big custom project. It seems like the reason I abandoned this before was cap size vs. the terminal cup and opening......lol

Just a bit irritated I can't get the correct values of all the caps and resistors from one vendor.

H9

soundfreak1

Used the munforf's in my 5jr+'s and worked fine. BTW if you would like I have a pair (I believe) of rt25 xovers you can have if you want to keep the originals intact.

heiney9

Really, soundfreak1? That would be great. Are yours the RT25i or just RT25?

H9

soundfreak1

Just the reg rt's bought them at a garage sale some years ago when I had a pair in a 5.1 system. The cabs were for fobar I needed 1 driver for my good pair and still have all the others and the xovers I think just need to open the box and see them again. Pulled them out of the cabs and packed them away. Also have 1 driver and 2 tweets as I remember.

soundfreak1

yep just found the box! 1 mw5522 driver, 2 sl5507 tweets and 2 complete original xovers. Also (forgot I hade these) 2 vifa 804 tweets from a pair of time frames 450's I think.

soundfreak1

I love finding sealed boxes of stuff I forgot I had. It's like Christmas all over again. Too bad I can't use them. LOL

soundfreak1

Heiney9, I believe they are the same? Is it just the cabinets that differentiate them?

heiney9

I know what you mean, I found a pair of M5 passives I forgot I had as well as recently hooking up a pair of Pinnacle speaker's I haven't listened to in quite sometime.

Let me peak at the crossover to familiarize myself again and then I'll let you know if I want those.

H9

soundfreak1

No prob. Have no use for them. There here if...

heiney9

So, going through some old parts odds n ends boxes I found the caps I bought awhile ago for this upgrade. Clarity caps and Aeon caps for the low pass and Mills.

Soundfreak1 if you still have those crossovers and they need a home, I'll take them.

H9

soundfreak1

That can work. Pm me your info. No charge for the xovers just cover the ship. They should fit into the P.O. 10.00 box. I will check as I think I have one to test fit.

heiney9

Not sure if I ever followed through with getting the x-0ver from Soundfreak1. I didn't run across them in the move.

Finally all moved, have been since the end of September. My dedicated listening room is not even close to being set up, but now is the time to start working on it since the main part of the new place is all done and unpacked, etc.

The basement is finished with a rec room and bar and a separate room for an office. I am getting my office rig up and running this long Thanksgiving weekend. One of the featured speakers will be the RT25i's after I rebuild the x-overs. I just bought a minty pair of x-0vers to work on so I can keep the originals if I somehow eff one up.

Once I get back in the groove of soldering and methodically placing parts on a PCB, I'll upgrade the R200 crossovers.

I bought the caps and resistors from Partsconnexion because of a 25% off sale. They didn't have the correct air core inductor. I have the schematic for the RT25i and steel laminate inductor I'd like to replace. The other inductor is originally an air core so I think I can leave it alone.

My question is the schematic gives a dcr #, but the dcr rating on the Dayton air core inductors is 0.41ohms. I can get the exact 18 AWG 0.70mH air core, but the schematic shows 0.20ohm for DCR. Should I be overly concerned or it always the lower the DCR the better?

Jantzen air core inductor same as above states DCR @ 0.40ohms

Also, how the eff do you deal with the glued on parts? How to loosen the glue?




H9

VR3

You probably need a 14 awg inductor for the mid

https://www.hificollective.co.uk/catalog/ccesa830-91uf-250vdc-claritycap-range-polypropylene-p-7785.html

VR3

Glue can use a heat gun

Also the rti boards are very low quality with extremely thin traces.

Be careful

heiney9

VR3 wrote: »

You probably need a 14 awg inductor for the mid

https://www.hificollective.co.uk/catalog/ccesa830-91uf-250vdc-claritycap-range-polypropylene-p-7785.html

So going to a smaller gauge of wire lowers DCR?

One of the reasons I bought a 2nd set of x-overs was in case I eff them up. It gives more peace of mind. And these look to be untouched and I paid like $25 for the pair.

Thanks

H9

heiney9

VR3 wrote: »

You probably need a 14 awg inductor for the mid

https://www.hificollective.co.uk/catalog/ccesa830-91uf-250vdc-claritycap-range-polypropylene-p-7785.html

Originally when I started this thread I went with some cheap Clarity APW caps 9.0u, but read they weren't really that good.

I couldn't find the 9.0u that you linked to anywhere. Forgot about HiFi Collective out of the UK.

I ended up going with these as a compromise. I did some reading the Audionote electrolytic are very similar to the now defunct Black Gate caps. It fit, it was the right $$$ for this job and they get good press for how they sound.

https://partsconnexion.com/audio-note-electrolytic-capacitor-6-8uf-50vdc-seiryu-series-non-polarized-radial/

AND

https://partsconnexion.com/claritycap-capacitor-2-20uf-250vdc-px-series/


The PX Clarity's have always been a favorite.

Also when did Mills resistors get so pricey!! A matched pair of 2u 5W are $14. They used to be $2-3 a piece.

H9

F1nut

Dap lots of denatured alcohol on the glue keeping the glue wet. After 5 minutes it should peel right off.

VR3

Bigger wire, lower dcr

Don't recommend using electrolytic caps, even black note in speakers

bcwsrt

I had to run and get some at the local Walmart because all I had on-hand was 70%, but @pitdogg2 used 91% isopropyl alcohol when he worked his magic on my RTA 15's. He applied like Jesse described and it worked great to remove the 30 year-old hot glue on those.

heiney9

VR3 wrote: »

Bigger wire, lower dcr

Don't recommend using electrolytic caps, even black note in speakers

Duh, 14 is larger than 18 AWG.......my brain wasn't working properly...lol

F1nut

Should have been dab, not dap.

heiney9

Just set-up (kind of crudely) the RT25i's. Qobuz through the Keces E40 integrated with dac (asynchronous USB) MIT AVt 3's.

I forgot how damn good these sound!! Certainly worthy of a x-over refresh/upgrade. Amazing what incredible sound comes out of such a small box. These could literally fit inside the R200's and still have room.

Feel like I'm in the front row of a Norah Jones concert.

Crazy good.

Going to get out my tube integrated's too.






H9

heiney9

The question is do I spend an additional $80+ on inductors and better 9.0u caps. I feel like maybe holding back and going with something superior to the originals, but perhaps not top shelf is more rational. I could use the $80+ for part of a no holds barred upgrade for the R200s, which will always be the main speaker.

I've got about $85 (including an add'l pair of x-overs) in them now.

My thought was I could use the RT25i's in a 3rd rig. I purchased one of these to build over the Winter. I have an excellent minimalistic pre-amp to go with it. I think the RT25i's would be perfect.

A beefed up Nelson Pass "Amp Camp Amp" (ACA MiniMax)

https://diyaudiostore.com/pages/project-aca-minmax

H9

P.s. I finally have a large work space to actually do some quality DIY work. I am by no means an expert, but taking my time and with a little guidance I think I can do.

VR3

The main issue is where you plan to put it. The crossover is going to take up substantial real estate in such a small enclosure