Electrolytic cap replacement-RT7 crossover

[speakergeek]

Can you guys recommend a superior capacitor replacement for the 9.0 uf electrolytic cap in this crossover? Also what is the crossover frequency? Thanks!!!!

[Tbone289]

I would recommend removing the bypass cap and using two 4.7uf caps in parallel to replace C2 & C3. 9.0uf are harder to find and don't fit the stock terminal cup as well as the smaller 4.7uf in parallel. This will still keep you within 2% of the stock 9.47uf (C2+C3) spec. A bypass cap is not needed, nor even desired, if good-quality poly caps are used.

See my RT7 upgrade pictorial at the link below. I have since put the stock inductor back in, because the one I used for the mod didn't match stock DCR:

http://www.polkaudio.com/forums/show...rade-pictorial


If I were to do it again, I would use Clarity caps rather than Dayton. I've used Clarity PX caps a few times since I did the RT7 upgrade, and they sound great even at their modest price point. If cost isn't as much of a concern, I would use a higher-grade Clarity brand or Sonicaps.

http://www.madisoundspeakerstore.com...ropylene-caps/


EDIT: I've never calculated the crossover frequency. I figured Polk got it right, so I just stayed within spec.

[thsmith]

What Tbone said but I will throw in sonicap as another cap option.

[Tbone289]

This will still keep you within 2% of the stock 9.47uf (C2+C3) spec.

I miscalculated there. 2 4.7 caps would keep you within 1% of the 9.47uf spec with the bypass removed.

[thsmith]

4.7uF / 200VDC 0.92 x 1.27 $12.87


http://www.soniccraft.com/sonicaps.htm

Put them in parrallel like this.

[Tbone289]

If you use the pictures in the RT7 upgrade link I posted above, you can see one way to mount them to fit in parallel on the RT7 board.

[westmassguy]

Can you guys recommend a superior capacitor replacement for the 9.0 uf electrolytic cap in this crossover? Also what is the crossover frequency? Thanks!!!!

Sonicap makes the 9uf and 2.2 uf cap, no need to parallel anything, and ditch the .47 Mylar. While you're at it, order 1 ohm Mills MR-12 resistors too.

[F1nut]

Sonicap makes the 9uf and 2.2 uf cap, no need to parallel anything, and ditch the .47 Mylar. While you're at it, order 1 ohm Mills MR-12 resistors too.

^This^

[Tbone289]

Indeed, if you can make the 9uf fit, it's the better option. I couldn't, so I went with the parallel 4.7's. Not using the bypass cap has obviously been covered.

[speakergeek]

So I ended up doing a prretty major change to this speaker. I can say that it was most definitely a change for the better. I initially got carried away with the c/o design possibilities, so I just decided to upgrade the c/o and the drivers. I went the SEAS tweats and woofs plus a custom c/o from Madisound. Here are some shots of the build:







The cross-over consists of ESA Clarity Caps in the tweeter circuit and a Goertz 14g copper inductor plus SoniCap Fast Caps in the woofer circuit. Also the resistors are Mundorf MOX. All inductors are air core. Sounds absolutely great! Cheers.

[Face]

I'd say that's a big upgrade. Congrats!

[speakergeek]

I'd say that's a big upgrade. Congrats!

Yes sir! The overall improvement in SQ has been profound. Thank you for the compliment. Trying to describe the change is difficult, but simply put the speakers seem much larger with considerably better mids and highs.

[Face]

It's hard to tell from your image, but is the tweeter flush mounted? If not, and you're capable of doing so, flush mounting would make them sound even better.

[speakergeek]

It's hard to tell from your image, but is the tweeter flush mounted? If not, and you're capable of doing so, flush mounting would make them sound even better.

I'm working towards that very goal. I want to do it right. I realize there are phase lobe issues etc. but even so, they new arrangement sounds great. My mains have a slight tilt backwards already.

[Face]

If you know how to use a router, this kind of bit may help: http://www.mlcswoodworking.com/shops...ng6_kit_anchor

[F1nut]

The cross-over consists of ESA Clarity Caps in the tweeter circuit and a Goertz 14g copper inductor plus SoniCap Fast Caps in the woofer circuit.

That's not a Sonicap, it's a Solen.

[speakergeek]

That's not a Sonicap, it's a Solen.

Yes you are correct. My bad....

[westmassguy]

Very nice work, but technically it's no longer a Polk

[speakergeek]

Very nice work, but technically it's no longer a Polk

You are correct. I like the cabinet though. Keeping it in place really emphasized the difference in upgrade though.

[speakergeek]

I did rename these speakers. Now they are CS-7 mk.1...

[speakergeek]

It's hard to tell from your image, but is the tweeter flush mounted? If not, and you're capable of doing so, flush mounting would make them sound even better.

Here is a short term "flush mount solution" I came up with. I cut a diffraction baffle from cardboard and covered it with a thin coat of black colored wool. Honestly I think it sounds better than before-possibly better than pure flush mount? THoughts and speculations please. Don't chew me up too bad...

[Face]

It will probably help, but still isn't correct. :)

[speakergeek]

It will probably help, but still isn't correct. :)

How much incorrectness will be corrected?.....?? Honestly, I'm haapy with the result so far...

[DON73]

Many years ago I bought a pair of RT5s and when I heard them in my home I thought "these are the easiest listening speakers I own" Packed them up and rushed back to the store to trade for what I assumed would be an even better speaker the RT7s. Rushed
home listened then packed the RT7s up and rushed back to get my RT5s back but they were sold.

[speakergeek]

Many years ago I bought a pair of RT5s and when I heard them in my home I thought "these are the easiest listening speakers I own" Packed them up and rushed back to the store to trade for what I assumed would be an even better speaker the RT7s. Rushed
home listened then packed the RT7s up and rushed back to get my RT5s back but they were sold.

The RT7 was a great speaker for many years for me. Recently though the sibilance and mids that used to be were gone. Thought it could be the electolytic cap in the crossover being bad, or possibly just the tweets wearing out. Started exploring the possiblity of rebuilding the crossover, then just decided to upgrade the entire speaker set and get a good crossover to go with them. So far very happy with the result, although I no longer have true Polk Audio speakers any more.

[DON73]

The RT7 was a great speaker for many years for me. Recently though the sibilance and mids that used to be were gone. Thought it could be the electolytic cap in the crossover being bad, or possibly just the tweets wearing out. Started exploring the possiblity of rebuilding the crossover, then just decided to upgrade the entire speaker set and get a good crossover to go with them. So far very happy with the result, although I no longer have true Polk Audio speakers any more.

You did a fine job on all the modifications! Doesn't matter what they are now.......your enjoyment of them is what's important.

[speakergeek]

You did a fine job on all the modifications! Doesn't matter what they are now.......your enjoyment of them is what's important.

Thanks man! The latest configuration has given me several grins...