Recapped my RTA 12c speakers

drksun

Hey guys, first time posting. I've been lurking around this site for a month or so trying to get all the details to recap a set of RTA 12c speakers I recently purchased. This is my first real pair of speakers, I'm running them on an NAD 7250pe amp I also purchased used. I got the speakers for $125 and the amp for $60 from a local audiophile that sells/collects vintage audio.

I used the following components for the crossover upgrade:

Everything is from Erse, parts and shipping was cheap, about $30. I could of gone with all poly caps and Mills resistors but I took a cheaper route as I couldn't justify spending more than I payed for the speakers to rebuild the crossover. I went with 10W resistors as recommended on here, the 5W resistors on the internal crossover board seem to get very hot as the circuit board was scorched and the foam melted around this component on both channels. From my understanding resistors will change value when out of "standard" operating temps.

4x 4.30μF 250v PulseX Metallized Polypropylene Film Capacitor (Original value 4.4uF)
8x 25.0?F - 100v - 3% D.F. - Non-Polarized Electrolytic Capacitors (Original value 27uF)
2x 56.0?F - 100v - 6% D.F. Non-Polarized Electrolytic Capacitors (Original value 55uF)
2x 2.0Ω 10W wire wound resistor. 5% tolerance (Originally 5W)
2x 7.5Ω 10W wire wound resistor. 5% tolerance (Originally 5W)

Album:
http://imgur.com/a/Er7NP

F1nut

Welcome to Club Polk.

I don't mean to rain on your parade, but replacing electrolytic caps with the same defeats the purpose of upgrading the crossovers. Did you replace the polyswitches as well?

As for the money, many of us have more into upgrades and tweaks to our speakers than what we paid for them. The rewards far outweigh the cost.

Tip: raise the resistors off the board, no foam under them, to get as much air flow as possible around them, which will help them stay cooler.

westmassguy

Welcome to the Forum.
I agree with F1nut however, especially with the NP Electrolytics, and the resistors. Dayton 5%, or Solen Fast Caps for the NPs, are relatively inexpensive, and are good quality. Mills or Mundorf resistors are also far superior to the wire wounds, and not very expensive either.
The only time I used NP Electrolytics on my Polks was when I recapped my SDA-2As, which required two 130uf caps per crossover to make a ginormous 260uf in the low pass section. Didn't have the cash, but it's definitely on my short " to do list".
It looks like you left the polyswitches in place also.

drumminman

While replacing the old, worn out electrolytics will probably improve the sound, using film caps would have been better. The old saying you get what you pay for comes to mind.

I rebuilt the Xovers in my 12C's and, though expensive, used mills and Sonicaps. The speakers never sounded this good when I bought them new!

The way I looked at it when deciding how/whether to do this is for the cost of the parts (the cost of the speakers had long ago been amortized!) could I buy anything that would sound as good or better.

Enjoy your speaks and know that if you decide to go the full monty, you'll be rewarded.

drksun

westmassguy wrote: »

Welcome to the Forum.
I agree with F1nut however, especially with the NP Electrolytics, and the resistors. Dayton 5%, or Solen Fast Caps for the NPs, are relatively inexpensive, and are good quality. Mills or Mundorf resistors are also far superior to the wire wounds, and not very expensive either.
The only time I used NP Electrolytics on my Polks was when I recapped my SDA-2As, which required two 130uf caps per crossover to make a ginormous 260uf in the low pass section. Didn't have the cash, but it's definitely on my short " to do list".
It looks like you left the polyswitches in place also.

Yeah I was thinking about replacing the polyswitch with a fuse or jumping it, my amp isn't that powerful anyway.. I was originally going to use Dayton 5% or Axon truecap, but I would of ended up spending around $80. I still consider this an upgrade since the old parts are close to 30 years old. Keep in mind this is my first set of nice speakers, I don't have the experience to differtiate suttle differences in sound but I defiantly noticed that the lows go lower and louder now.


My next plan is to dynamat the drivers and dampen the inside the cab, but a few of the screws mounting the drivers have stripped the threads and turn infinitely when I try to in screw them, any ideas? Sounds like I sould put in hurricane nuts after I get the speakers out.

westmassguy

Hurricane nuts are excellent. I did all my Polks with them. Parts Express carries them, Size #8-32. You'll also need a 13/64" drill bit, and machine screws. I found these on eBay: http://www.ebay.com/itm/330611643249?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649 and they're a dead ringer for the original sheetmatal screws.

F1nut

Yeah I was thinking about replacing the polyswitch with a fuse or jumping it, my amp isn't that powerful anyway..

You are more likely to push a low powered amp into clipping than a high powered amp. That said, you should keep the polyswitch in the circuit, but replace with new.

drksun

F1nut wrote: »

You are more likely to push a low powered amp into clipping than a high powered amp. That said, you should keep the polyswitch in the circuit, but replace with new.

got it thanks, i forget that it's not the "power" that destroys speakers, it's the clipping and it has to do with the headroom of the amp. For what it's worth my amp has a "soft clipping" feature which i assume is some type of limiter/compressor? As a test can't i jump the two end of the poly switch to test the difference in sound quality as long as a don't drive my amp too hard and clip it (I've never gone past 50% of full volume as it gets too loud for my bedroom)

Thanks!

bookshelf^love

Hows the sound, and driveability of the RTA after the capping? Can you hear more clarity on the top end?

F1nut

As a test can't i jump the two end of the poly switch to test the difference in sound quality

I suggested replacing them since they are most likely the originals and who knows what condition they are in. However, I forgot about NAD's soft clip feature, so you'd probably be ok without the poly's. Just remove them and replace with a jumper or resistor.

drksun

bookshelf^love wrote: »

Hows the sound, and driveability of the RTA after the capping? Can you hear more clarity on the top end?

The main thing I noticed was extension of the lows, they sound "lower" and louder than before. From my understanding the low freq crossover point is determined by an inductor but the capacitor modulates the slope? I have noticed that the highs seems brighter but sound fatiguing as they did before.

What about the caps in my amp? My NAD amp was also made in the 80's... When I can afford it I think I'm going to just get a different amp with more modern components.. I don't know if I should prioritize the amp over dynamating and treating the speaker cabs..

F1nut

Ok, a couple of things....

Do you still have the original tweeters installed. If so, are they the SL2000's?

How many hours do you have on the new crossovers?

There's a reason for using better caps and resistors, you may be finding out why.

drksun

F1nut wrote: »

Ok, a couple of things....

Do you still have the original tweeters installed. If so, are they the SL2000's?

How many hours do you have on the new crossovers?

There's a reason for using better caps and resistors, you may be finding out why.

Yes original tweeters, sl2000
Maybe 10hr on the crossover :-/

I've been super busy this summer with studying for my mcat, wish I had more time to listen. Honestly I don't think I have enough experience to evaluate how the speakers sound before/after the recap. I can only assume that the 30 year old caps were out of spec and the new ones are a lot closer (worth the $30 in my book).

Can I just leave the speakers on at a low volume playing music (maybe 10 watts) to burn in the caps or do they need a significant load?

F1nut

It wouldn't matter what caps/resistors you put in them, those SL2000's would still sound awful. Get the RD0194-1's.

You need 200 hours, so just let them play. The volume doesn't matter.

drksun

Any idea if I will benefit from a new amp? I was thinking about an adcom 535 (around $100-150 USED) or the emotiva x-100 ($200 new). I'm more interested in fidelity and sound-stage than massive output but the extra headroom is appreciated. Trying to stay under $300 new or used. The only thing I'm worried about vintage amps is having to replace old parts as it's a lot more work than recapping a crossover. Thanks

MFattal

drumminman wrote: »

While replacing the old, worn out electrolytics will probably improve the sound, using film caps would have been better. The old saying you get what you pay for comes to mind.

I rebuilt the Xovers in my 12C's and, though expensive, used mills and Sonicaps. The speakers never sounded this good when I bought them new!

The way I looked at it when deciding how/whether to do this is for the cost of the parts (the cost of the speakers had long ago been amortized!) could I buy anything that would sound as good or better.

Enjoy your speaks and know that if you decide to go the full monty, you'll be rewarded.

@drumminman

Could someone kindly list what would be needed to recap two 12c crossovers? I liked how @drksun wrote the old and new values but have no clue what the engineering side of things is supposed to be like. I also live abroad and technical expertise is not great so I'll be shipping them to Cairo and figuring it out from there. A list of all parts needed would be exquisite and appreciated.

Thank you.