Jumping in the water again... Polk RTA-12Bs...

jon s

I upgraded my Polk 10Bs with Jantzen crosscaps and also experienced an improvement. I then upgraded it with Sonicaps and the improvement was greater than from stock to Jantzen soundstage-wise. That's why I went from stock to Sonicaps on the RTA-12C. I just got my RDO194s for the RTA-12C and will probably set it up tonight...

jon s

I finally set up the RTA-12Cs on Monday, ran them 24x7 (so about 120 hours)... Figured it's time to start evaluating the RTA-12Cs against the modded Monitor 10Bs.

Well, no surprise, the sound is very similar, in fact the only differences is that the RTA-12Cs sound a bit smoother on the top (since the RDO194s crossover at 3kHz on the RTA-12Cs iso 2kHz) and the bottom end is tighter and goes a tad lower than the Monitor 10Bs. Both speakers sound very musical and smooth with the Sonicaps installed. They sound nearly identical in timbre. The differences are so slight (what do you expect, same drivers...), you need an immediate direct A-B comparison to tell the differences.

Imaging is also very similar, in fact, I was hard pressed to notice a difference between the RTA-12C and the Monitor 10s. The RTA-12C has a little better depth. The imaging was slightly improved when the top hats were installed. Looking inside the top hats, there is also a little ramp that joins with the ramp on the crossover board under the tweeter. I figure it must help the dispersion a bit more. One noticeable effect with the top hats is that it definitely affects the tweeter response. The cloth covering the top hat is very thick so it must be attenuating the highs a bit.

The RTA-12Cs need more power than the Monitor 10Bs. My 80-wpc Sony TA-8650 V-FET amp volume knob is normally set at 9 o'clock with the Monitor 10s. The RTA-12Cs need to be set at about 10 o'clock. The 4-ohm impedance requires a lot of current as the amp runs out of power quickly at moderately loud volumes (the V-FET amps do not perform well at 4-ohms anyway).

So I am waiting for the Acurus DIA-100 100wpc amp I purchased earlier. It can deliver 150wpc at 4-ohms but the important thing is that it can handle low impedance loads. i am also considering connecting a Nakamichi PA-5 Stasis Class-A amp to the speakers to see how it sounds, but I need a pre-amp first.

Would i recommend the upgrade on a RTA-12C? Yes. But the cost of upgrading the RTA-12Cs is several hundred dollars when using Sonicaps and also replacing the SL2000s. Upgrading the Monitor 10s is about half the price and the differences are subtle indeed.

Postscript: on a whim, I decided to see what affect using bypass caps on the high frequency circuit would do. The bypass caps made a notable difference in the sound... all negative. The music was harsher, losing its smoothness. Imaging suffered, individual pieces were smeared and the soundstage collapsed. F1Nut is right, do NOT use bypass caps with the Sonicaps. You are just wasting your money and it just ruins the overall sound.

schwarcw

Your setup looks terrific! Congrats on the quality Polks and your crossover upgrade. The Sonicaps will take a while to really settle in. I'd give them about 200 hours. The first 50 -75 hours is where the big changes will take place. I definitely think you need a big boy amp for the RTA-12's. You'll be amazed what 200 wpc will do for the depth of the sound stage and the overall presentation. If I were you I'd begin planning for a tube preamp and a nice big SS power amp. The tubed pre will make the music and voices fluid, smooth, almost magical. I like the dynamics of a SS power amp. Good luck and congrats!

nikolas812

Your setup looks very nice indeed. Congrats on getting everything wrapped up.

If I am not mistaken those 12's need BIG POWER. I might be wrong but aren't they rated a 500wpc a peice? I don't think they will really shine until you feed the hungry beasts. I would imagine there would be a big difference between 12's and 10's when powered properly.

Just my opinion.

Nick

jon s

just as a point of interest, I dragged out my Polk LSI15s and did a comparison between them and the RTA-12Cs... The RTA-12Cs sound more open, depth is better. The LSi15s sound smooth but the top end has no extension, sounds like there was a high filter engaged on the amp. I remembered that the Polk Model 10Bs sounded similar until I upgraded to the Sonicaps. After the Sonicap upgrade there was a definite increase in the HF in extension without adding any increase in the level of the treble.

On the other hand, the LSi15s have a deeper bottom end than the RTA-12Cs. It seems just a tad boomy at the extreme lower octave versus the RTA-12Cs which sounded a bit tighter... could be because the lack of deep bass on the RTA-12Cs made the bass tighter.

After investigating the crossover of the LSi15s, I decided to upgrade the tweeter caps to the Sonicaps (cost ~$100 for two 12-uf and two 18-uf caps) to see if I can get the best of both worlds. I cannot upgrade the midrange caps because of how the crossover is built. The midrange and bass sections of the crossover has extremely limited space to work in and larger caps just would not fit... luckily the HF crossover is seperate from the rest of the crossover board.

In order to replace the caps, I have to remove the 8" woofer from the LSi15 and work through there. The internal wiring was made to exact lengths and there is no slack to pull out the crossover through the binding plate opening. More to come (once the caps come in)...

heiney9

Jon,

No disrespect to your Sony, but once you either get the Acurus or Nak hooked up the differences between the 10's and 12's might become more apparent. Also the LSi's don't seem to ever sound their best on a lower power/current receiver or int. amp. So I suspect those will sound better as well.

You and I have discussed the Nak amp before. Great performer, excellent highs, liquid mids, just a tad bass shy for my tastes. Get yourself a nice musical pre and go to town.

Keep us up on what's happening gear wise.

H9

P.s also a very minor correction to you eloquent post; the Nak is not a class A amp. It's an A/B amp which has a high idle current, which is why it runs so hot. IIRC, Nelson Pass stated the PA-5 runs in the 5-10W range in class A. (don't quote me on that):D

jon s

I know the Sony does not work well wth low impedance speakers. It does its job with the Polk Model 10Bs but barely suffices with the LSi15 and is lackluster with the RTA-12Cs. The amp is 32 years old and weighs 50 lbs which is heavy for a 80-wpc unit.

The Acurus should be here Friday or Saturday at the latest (I hope)... Looking at the Acurus groups, there are a lot of little mods that people have been doing to improve the sound to make the amp more open. Most of them involved replacing the cheap caps used, replacing them with Sonicaps (who doesn't use them now???). According to Stereophile, the Acurus handles low impedance loads quite well.

Unfortunately, i have to have someone look at the Nak, while moving it, i heard something rattling loose inside the case... opened it up and could not find anything loose. don't want to have it short somewhere with a loose object inside.

heiney9

jon s wrote: »

I know the Sony does not work well wth low impedance speakers. It does its job with the Polk Model 10Bs but barely suffices with the LSi15 and is lackluster with the RTA-12Cs. The amp is 32 years old and weighs 50 lbs which is heavy for a 80-wpc unit.

The Acurus should be here Friday or Saturday at the latest (I hope)... Looking at the Acurus groups, there are a lot of little mods that people have been doing to improve the sound to make the amp more open. Most of them involved replacing the cheap caps used, replacing them with Sonicaps (who doesn't use them now???). According to Stereophile, the Acurus handles low impedance loads quite well.

Unfortunately, i have to have someone look at the Nak, while moving it, i heard something rattling loose inside the case... opened it up and could not find anything loose. don't want to have it short somewhere with a loose object inside.

I am familiar with the Yamaha V-FET amps and Sony was the only other manufacturer to use V-FETS. Somewhere I have a whole bunch of info on V-FET's. They are no longer made and the NOS that you find are extremely expensive. If you like the sound signature of the Sony take extra care with it. Personally, I never understood and still don't understand all the "worshiping" Yamaha collectors seem praise upon the B1 and B2 V-FET amps. To me they sound just like normal Yamaha amps which in my experience is rather mediocre.

Acurus is the "budget" line of Aragon (Dan D'Augustino who was part of the Krell design team helped with the first series of Aragon amps) when they were owned my Mondial before Klipsch bought them out.

My brother's DIA 100 does an excellent job of driving his LSi 9's and now his LSi 7's. Alot of thought and R&D originally went into coming up with a satisfactory sounding passive line stage pre-amp section for the (2) DIA models. I'm surprised they used "cheap" caps in there. With any design there is always room for improvement if you want to spend the cash. See what it does first before jumping on the "upgrade" wagon. Although I don't doubt if you want to spend $200-300 on upgraded caps that they will make a difference. It's probably an excellent platform for these types of things.

H9

jon s

Well, my wife just called and it appears the Acurus DIA-100 just got delivered to my house so i will see how that goes...

Regarding V-FET amps... I also owned a Yamaha C-2/B-2 preamp/ V-FET amp combo and agree. The amp sounded real smooth but just did not really excite me. It was just too bland for my tastes.

i really love the Sony TA-8650 amp but it does have a couple nitpicks... one of course is that it does not perform well with 4-ohm speakers, second they must have the WORST terminals to connect the speaker wires to and finally, they get SUPER hot. I had the amp worked over by Glen McDonald of AudioKarma.org. He replaced all the caps and diodes as required. He is an excellent tech if anyone needs anything worked on. His tag name is EchoWars. The only catch is that he does the repairs on the side and you might have to wait awhile before he gets to work on a unit (mine took a few weeks)...

heiney9

jon s wrote: »

Well, my wife just called and it appears the Acurus DIA-100 just got delivered to my house so i will see how that goes...

Regarding V-FET amps... I also owned a Yamaha C-2/B-2 preamp/ V-FET amp combo and agree. The amp sounded real smooth but just did not really excite me. It was just too bland for my tastes.

i really love the Sony TA-8650 amp but it does have a couple nitpicks... one of course is that it does not perform well with 4-ohm speakers, second they must have the WORST terminals to connect the speaker wires to and finally, they get SUPER hot. I had the amp worked over by Glen McDonald of AudioKarma.org. He replaced all the caps and diodes as required. He is an excellent tech if anyone needs anything worked on. His tag name is EchoWars. The only catch is that he does the repairs on the side and you might have to wait awhile before he gets to work on a unit (mine took a few weeks)...

For vintage stuff Echowars (Glen) is the man. He has a great rep. and based on others testimonials I wouldn't hesitate to send him a vintage piece to restore.

I'll be anxious to hear your impressions of the the Acurus. I have some LSi 7's on the way but they didn't come early. They are tracked to be delivered tomorrow.

jon s

heiney9 wrote: »

For vintage stuff Echowars (Glen) is the man. He has a great rep. and based on others testimonials I wouldn't hesitate to send him a vintage piece to restore.

I'll be anxious to hear your impressions of the the Acurus. I have some LSi 7's on the way but they didn't come early. They are tracked to be delivered tomorrow.

yeah... he really did a good job on the amp... I think it set me back about $800... $200 to ship to him, $300 for repairs and $300 to return (and this was two years ago). If I were to send something back and forth now, I think the price would be doubled. It is painful sending things to/from Hawaii, especially with the price offuel now... UPS and Fedex is outrageous. Now i have to ship USPS to save some money...

jon s

OK, set up the Acurus DIA-100 amp and been doing some listening... the amp has some pluses and one minus...
pros...
slightly better depth and width in imaging
slightly better focus
runs cooler
slightly more open

cons
treble seems a bit louder than the Sony. Loud enough to notice that the 10Bs now sound on the bright side. Conversely, the LSi15s now sound balanced whereas it sounded a bit muted with the Sony amps. I noticed that Stereophile review did note that the sound was a bit bright.

jon s

Update on the RTA-12Cs... have them playing on the Acurus DIA-100 amp... couple of notes.. that amp can pump out the decibels.. The RTA-12Cs gets REAL LOUD real fast on the Acurus. While the 10Bs get moderately loud before getting uncomfortable, the RTA-12Cs can fill the room louder with less strain, but you run out of power before the speakers cry uncle. The dynamic range of the speakers is unreal.

The bottom end is getting better and better. Where the 10Bs are lacking the RTA-12Cs are tighter and lower. The imaging and soundstage is slightly better than the 10Bs, but they sound a tad echoey compared to the 10Bs. I don't have too many hours on the 12s so i still have to break the new caps in some more.

Elmostro

I just bought a pair of 12B's and I'm going to replace the caps but i have no idea of what i'm doing, i found some caps on parts express here is the link
http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=027-439&scqty=8
http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=027-419&scqty=4
will they work?
thanks for looking

vstarkwell

Elmostro wrote: »

I just bought a pair of 12B's and I'm going to replace the caps but i have no idea of what I'm doing, I found some caps on parts express here is the link
http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=027-439&scqty=8
http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=027-419&scqty=4
will they work?
thanks for looking

@Elmostro
You are aware this thread is 3 years old? If I were you I would start a new thread in the "Speakers" section under "Advance Technical". You'll have a better chance of folks coming along to assist you.