RTA 12C's upgraded for forum member, w/ pics

geoff727

Hi folks,

This is a pair of RTA 12C's that I just finished a bit of work on; these belong to forum member filmfreak1138. He wanted some sonic improvements to these. The original vinyl veneer and grill cloth is still in good shape, so it was decided to leave it as-is.

These speakers received the following:

1. Crossovers (all 4) upgraded with a ClarityCap SA/AXON mix.

2. New, larger, taller, heavier bases built. Each base has 4 floor spikes on the corners.

3. New binding posts.

4. New wiring.

5. T-nut and metal screw driver and crossover mounting hardware.

6. Installation of 3-layer Sonic Barrier.

7. Replacement of original top crossover-to-enclosure connectors with newer, better ones.

8. Dynamat the driver baskets and JBWeld the driver magnets. Dynamat the passive radiators.

9. Give everything a good cleaning.

10. Re-do the finish on the grill logos.

11. Install RD0194's.

In the course of the work, I found (and re-did) several mis-drilled mounting holes for things, and one solder joint that was literally hanging on by less than a hair.

Okay, the details....and for some reason I took terrible pictures this time.

geoff727

This is what the innards of the enclosures looked like when the fill was taken out. First task was to remove all the excess glue and clean things up.

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Enclosures getting cleaned and painted...

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Holoes getting drilled out and T-nuts getting installed....

geoff727

Installation of Sonic Barrier after the enclosures were all cleaned and painted inside. I used a tremendous amount of hot glue (incurring a few burns along the way) to ensure this stuff does NOT come loose.

geoff727

Dynamat and JBWeld on the drivers and passives...

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Here's the new mounting hardware...

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The bases....

Each base is a particle board layered build-up, veneered and painted on the sides, with black melamine on the tops and bottoms. The bases enable the usage of 4 strong, widely-spaced floor spikes to give the speakers much-needed stability. Additionally, they raise the speakers 2 3/4 inches to put the tweeters at ear height from the listening seat. They add about 20-25 pounds per speaker.

I don't know as they necessarily add nor subtract from things cosmetically, but in person the speakers do seem to have a much more solid "stature" from the added height and reduction of top-heavy feeling. The added weight gives a more professional feel to the speakers, also.

geoff727

Most people know what the original crossovers on 12's look like, but here they are anyway...

The top crossover that goes on top of the enclosure is basically 'plug-and-play'. Screw it down in 2 spots, plug in the connector, and away it goes.

geoff727

Here is the comaprison of the new connectors alongside the original.

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Crossover boards cleaned and some parts ready to go...

That roll of stuff is the new gasket for the passives. I had to destroy one of the originals prying the passive off the enclosure.

The caps are ClarityCap SA's for the high-pass components. All other larger value caps are AXON's. New binding posts are Vampire BP Hex. New Mills MRA 12's. And, at the request of Roger, the owner, I replaced the polyswitches with fuse holders (ACME Audio cryo-treated ones), so he can use high-quality fuses in the future and still retain tweeter protection.

(Those 2 ClarityCaps equal 4.4uf paralleled together. They replace that one yellow cap).

geoff727

Everybody's favorite part, the crossovers....

Details:

-In rearranging components, I made sure that the Polk Audio logo was more visible.

-All labels on the caps are oriented with the printing on the PCB.

-All lead-out wires are dressed better.

-New gold-plated connectors (all driver hook-ups got these).

-To acommodate the size of the 4.4uf position, I had to raise the PCB off the inductor spools. To that end, I gave the boards much stronger stand-off's.

-Each cap and inductor on top of the board rests on a cut piece of vibration-damping vinyl (serious overkill, I know).

-Jumpers were replaced with Neotech OCC copper wire (overkill again, I know).

-The fuse holder is in the same spot as the polyswitch; most other components use the original placement (and many of the same holes) on the PCB.

geoff727

More...

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And more with a comparison to the original...

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Both finished...

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And the inner crossovers, which were a LOT easier to do than the top ones!

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Comparison with original...

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The hook-up of the new connector before mounting it to the enclosure...

Those familiar with the 12 wil know what the black-white-blue mean.

geoff727

A few random pictures...

Hmmm, what are those speakers in the back there?:rolleyes:

geoff727

And all finished up.

Once again, the digital camera flash makes most things look like crap. They actually feel a little sharper in real life than some of the pictures would suggest, I think. I hope that Roger will enjoy these. If he doesn't, I already know a confirmed buyer for them!

geoff727

The seriously fanatical will notice that the brass nuts that hold the crossovers to the enclosures have been highly polished.

Also, the grill pegs that hold the top hats on, I took off of the enclosures. I put them on the hats instead, as the hats are less prone to damage from handling their light weight. The enclosures got the 'cups' for the pegs.

With all the new stuff, I think each speaker gained about 30 pounds or so in weight. At the beginning, Roger wanted to solve a perceived harshness in the treble. I hope the 194's and new caps will give his ears that wish. My goal, after listening to them, was to increase clarity from the bass up through the midrange, and to attempt to solve what I perceived as a 'cupped hands' quality in the mid-bass/midrange region.

Tomorrow morning they go on the system....

cfrizz

All I can say is wow, great work!

fossy

very nice !!!!!!

brgman

Impressive,Beautiful work.Those xovers are the chit!

DaveHo

Holy smokes! Those are incredible!:eek: I have a pair of 12C's as well which could use some TLC. Do you ever travel to the east cost? Any idea how much the restore cost? I'm not asure if I'm that ambitious but if I were...

-Dave

Face

Very nice!

Conradicles

Great job and I bet you got one happy owner!

TennMan

geoff727 wrote: »

Here's the new mounting hardware...

It appears you used two different size t-nuts. What size are they?

I really enjoyed reading this post. Thanks for going to all the trouble to do it!

geppy1

Very impressive !! Could you give us an idea of the costs of doing the X overs was??
keith

geoff727

DaveHo wrote: »

Any idea how much the restore cost?

Well, they're not the cheapest crossovers to do. There are quite a few 27uf caps, and a 55uf + 4.4uf parallel in the tweeter circuit (which I used standard values of 56uf +3.3uf for). So, the price can really run the gamut on these, depending on what you want.

geoff727

TennMan wrote: »

It appears you used two different size t-nuts. What size are they?

Good eye. I used 6-24's for the tweeters. 8-24's on everything else. I think that's right.