Rebuilding Polk RTA 12B Crossovers

[Michael8it]

I finally got around to ordering (and receiving) my audio capacitors from Erse Caps, and spent the day rewiring my 12B crossovers.

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Here is my 'work area' and one of the crossovers on the left. I pigtailed the connections for upper and lower crossovers, and changed the wiring to a standard and easier to follow (at least for me) red and black, instead of black and white. If I get around to building new cabinets, I will eventually remove them. The connections at the lower crossover are reversed, so I can only hook the correct set of wires up inside the cabinet.

I had jumpered the fuses previously, and noticed less distortion in the tweeter. When I did this upgrade I removed the fuse holder completely. The new size caps required some drilling and a bit of rearranging but it all fits neatly on the board.

First impression is much much more detail. The more subtle instruments come through - it's kind of like taking cotton out of your ears. The bass also seems to have tightened up. The highs are a bit bright but I think this is due to the caps being brand new. In any case it made a distinct and very noticeable difference right out of the bat. Ill try to burn them in over Friday and Saturday and see how that affects things. But I am pleased with the outcome.

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[Michael8it]

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Notice the markings on the tweeters: They are 3514 not 5514 - apparently made in Denmark.

[halo71]

Looks like you did a nice job! I really need to get off my butt and order caps to redo the XO's on my RS-IIIa's.

[drumminman]

Did you decide to swap crossovers and replace the single Xover up top with the later versions (top Xover and one attached to binding post)?

Interested in hearing changes in sound either way, but especially if you did the swap.

[Michael8it]

Yes, I converted these from 12's to 12B's with the lower crossover. There was a better image with the 12 to 12B conversion, and the treble was quite a bit better, to the point where I took my EQ out of the circuit completely. The recap was quite literally like taking cotton out of your ears. The softer dynamics are there: the pluck on a classical guitar, the strings in the background behind a trumpet. I always noticed a dip or absence of frequencies in the Baratone range ( I could find an actual note ) and that seems to be more present now. I listened to some pieces from Canadian Brass and the trombones were right there in the mix.

Even with the 6501 drivers, there was a significant improvement when I switched to the 12B x-overs.

[Michael8it]

I have a conversion schematic for converting a 12 to 12B/C. You may find (as I did) that the values on the caps in an RTA 12 are hard to come by, so you wind up buy two to run in parallel to get the right value. Because of that, it was more cost effective to make these into the 12B/C system rather than the RTA12.

If you want the schematic PM me.

[drumminman]

I have a conversion schematic for converting a 12 to 12B/C. You may find (as I did) that the values on the caps in an RTA 12 are hard to come by, so you wind up buy two to run in parallel to get the right value. Because of that, it was more cost effective to make these into the 12B/C system rather than the RTA12.

If you want the schematic PM me.

Thanks for the offer Michael, but I have the 12C's which I completed modding about 6 months ago. IIRC my cap issues were more that Polk didn't strictly adhere to the values on their schematic! :eek: I don't think I was exact on some of the replacement values, but the ones I bought were much closer than the ones I replaced.

Glad you like 'em. I had an issue with one of my 2.3TL's when I first got them (pre-mods) so I hooked up one of the post modded 12C's in it's place with the other 2.3. It really held it's own in terms of clarity and even bass response.

Others have really disliked the SL1000's too, but I can't find fault with them. With my system they're smooth and refined - no harshness that I can detect. I may try the 194's one day, but I'm in no hurry.