RTA-12B Project

westmassguy

I've rebuilt quite few RTA-12 Crossovers, but never had the chance to get my ears on them, and do some cabinet upgrades. These were brought to my by the original owner. The first thing I did was a leakage test. I've never had a pair of Polks this tight. I pushed in and held the PRs on both. The woofers stayed out for a good 10-12 seconds, and then very, very slowly retracted over a 20-25 second time period. I disassembled everything, and found the Dacron in a heap at the bottom of both cabinets.
Sonicap Gen Is were chosen for the upper and lower Crossover sections. New Cardas Binding Posts were installed. The existing 3 pole connectors were retained, cleaned and treated with DeoxIT, along with the fuse holders.
The woofer's magnet assemblies were glued with Power Grab. Dynamat Extreme was installed in the woofer and PR frames. All existing gaskets were retained,
Hurricane Nuts were installed.
4" X 8" sections of Black Hole 5 were placed on the back wall behind each woofer.
The existing Dacron was re-installed in it's correct location, and tacked in place.
New black oxide, Torx head cap screws were used to secure the Woofers and PRs (I highly recommend them, no slippage).
A final leakage tests were done, and they matched the original tests, very tight.

RandyCroissant

Looks like a fun rewarding project, I acquired a pair of near mint m7 peerless that I plan to recap later this Winter. Let us know how they sound Dave.

westmassguy

They sound fantastic, even though they've not even begun to burn-in yet. I was struck by how tight the bass is on these. At first I thought it was less than my 2As, but it's not. It's fast and tight. That's about the only way I can describe it. The owner is picking them up next week.

RandyCroissant

That's great! One question what do you think about how little leak down they have and could this be something to look into for our SDAs

westmassguy

The MW6600X woofers have treated felt dust caps. I believe they are less permeable than the mesh used on later dust caps.

RandyCroissant

That makes sense!! thank you brother

pitdogg2

westmassguy wrote: »

The MW6600X woofers have treated felt dust caps. I believe they are less permeable than the mesh used on later dust caps.

I have to agree with this. My SDA1 Signatures use mw6600 except for dimensional mw6501 woofer. My woofers have always stayed out much longer than others who have done press test.

I wondered what the difference could of been.

Jazzhead

Nice work Dave! Those are going to sing - the customer is going to love them. I'm struck by how much tight, deep bass those RTA's can throw when everything falls into place.

westmassguy

Thanks Stephen

voltz

I would love to hear these sing! Nice work as always Brother!

If I had a week with those they would probably be broken in just fine when he picked them up

westmassguy

Thanks brother.

drumminman

Nice work Dave. I modded the xovers on my 12c's, plus did some other mods and used them for a while.
I later installed BH-5 and was really pleased at how it eliminated congestion in the mids (which I didn't realize was there until it was gone).
They image like crazy too!

westmassguy

drumminman wrote: »

Nice work Dave. I modded the xovers on my 12c's, plus did some other mods and used them for a while.
I later installed BH-5 and was really pleased at how it eliminated congestion in the mids (which I didn't realize was there until it was gone).
They image like crazy too!

Thank you sir. He's picking them up them morning

CH46E

Very nice. Are there (6) 27uf caps for each speaker? I was looking at the schematic and thought there was only 4 per?

CH46E

What did you think of the top end after the news caps? Would you say "fast transients, dynamic or lots of sizzle" ?

westmassguy

CH46E wrote: »

Very nice. Are there (6) 27uf caps for each speaker? I was looking at the schematic and thought there was only 4 per?

There are four 27uf, and a 55uf. Sonic craft doesn't make a 55uf, so I hand matched two 27s to equal 55.

westmassguy

CH46E wrote: »

What did you think of the top end after the news caps? Would you say "fast transients, dynamic or lots of sizzle" ?

Mo better everything, but I wouldn't say Peerless sizzle, they're very smooth. Have to burn-in for 200-400 hours before the caps completely settled in.

CH46E

Ahh. I just finished is he'd looking at the schematic and guessed you might have used two for the 55. Got ya. Thanks man.

CH46E

Well, I have 5501 tweeters in there now. And I like them better than the sl1000 I was using. The 5514 peerless were DOA when I got them.

I'm looking at a replacment and trying to decide BEFORE I change the caps and resistors. So i can accommodate any tweeter I put in there with adjustment.

I'm really wanting to try a AMT airmotive tweeter in them. Looks like they can play low enough for the oem values of the x over and give me the speed I'm looking for.

I've been watching for the 5514s on the bay but no luck.

I am finding the 5501 to be to sloppy and muddy for my likeing. At first I liked them over the sl1000. The longer I listen the less I like them.

5 years in US Marine's helicopters has caused a tad of hearing loss and now I seem to need a brighter tweeter.

westmassguy

I'd go with the RDO-194s

CH46E

If I go with the 194 should I leave the stock values in the recap?


After I did a recap in my JBL L80T I was told that switching from electrolytic to film I should add a small amount of resistance to the resistors?

What say you?

pitdogg2

CH46E wrote: »

After I did a recap in my JBL L80T I was told that switching from electrolytic to film I should add a small amount of resistance to the resistors?

What say you?

I'd say that was bad advice. 12uf electrolytic is the same as film except the electro will go bad with age where film will not have any electrolytic to dry out or go bad. The film should not shift values with age.

westmassguy

CH46E wrote: »

If I go with the 194 should I leave the stock values in the recap?


After I did a recap in my JBL L80T I was told that switching from electrolytic to film I should add a small amount of resistance to the resistors?

What say you?

There is a measurable difference in ESR between film and NP Electrolytics. It is frequency dependent, as it should be. Will you hear a difference in SPL? Extremely doubtful.

CH46E

I'll go with the 194s. Should I leave all the values oem or should I adjust anything.

I've decided to go with the Clarity caps entry level caps.

pitdogg2

As close to oem as possible. Only difference in my rebuild was to put higher rated resistors in my sda's switched out the 5watt for 12 watt but same ohm value.