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In Reply to: RE: miss the Telarc Organ Symphony posted by josh358 on January 14, 2017 at 12:12:35
The Theta Intrepid goes for about $1-1.3k giving you 5 channels for 1/3rd the cost, Effectively $600 or so per channel pair. The downside is that because it is a non feedback design it has weak bass and midbass performance. Because of this, and because of the particular attention Reich puts into midrange and treble performance it should do the tweeters and mids a better service than any of the JC designs. My only caveat is that being a DC servo it might have a slight low level resolution problem as the TIVa mids have and the Neo8 do but to a much lesser extent. I have not found any review to mention that it is an actual performance limitation.
Of course, the Theta Intrepid is not going to drive the bass panels. It also needs a real ground so requires that you have 3 phase wiring in order to avoid hum..
The other issue and downside of a non feedback balanced design is that the THD is rather high in the presence of bass and IMD on adjacent freq tests would be higher. But it is 3rd order so rather innocuous. This is not far from my old DR-9 design (from which Reich derived the Theta line) in general behavior and I can assure you it works fabulously on both mids and tweeters. Class A operation is 8-10W as tuned at the factory, you can bias it up further but the amp does well in the class B portion of its output so it is not as critical as it is in the JC and Emotiva designs..
Follow Ups:
I read the review last night. The price is certainly great, but there are a couple of issues -- it won't drive the woofers, as you point out, so I couldn't use it for my split woofer experiment.
And then there's the ground loop issue. I'm about to try an experiment with my computer, I got a fanless power supply, low noise video card, and liquid cooler for my computer, and I'm going to see if it's quiet enough to use in my living room. But I have to disassemble it to install the components. Once I've done that, I can try reconnecting the ground on the A-21. I fear, though, that I'm right and truly screwed, even though I swapped breakers so that everything driving my audio gear is now on the same phase. Even an isoground system probably wouldn't fix the hum fields in this house (my tech power is isolated ground but I had to repurpose some existing circuits for my audio and the contractor didn't put in the access hatch I asked for so I'd have to rip open the walls to run new ones).
Without a real well grounded 3 phase supply I don't think the linear Theta amps are a practical reality. So unless you manage to sort that one out I think those are out.
On the other hand, there is more flexibility in having high feedback and much cheaper high power amps for the bass panels rather than using the much more refined and expensive JC multichannel. Think linear Crown mactrotech 2402 which you can buy by the dozen at the price of the A51. Or 3X 3600 or 3602. Though some surgery to replace the fans is necessary.
I don't have that kind of heads on comparison to rely on. The closest I did on comparison was with the mg20.1 + big Chords vs. Big Boulder. and on the Apogee Diva - Big Krell KSA vs. Classe monos VTL Wotan or Siegfried tubes and a couple of others.
The comparables are just that class A high power gives you a more tuneful tighter bass with subjectively deeper extension. It also heats the room very quickly. Even a large room. Tubes don't damp the membranes well enough and lose on tightness, making the bass sound a bit bulbous or elephantine. The class A/AB like the Classe was nearly as tight as the class A Krells but apparently started sagging. Some say the KSA bass is not natural. Compared to the rest of the things put on the Diva bass - or whole speaker, the Krell bass was most convincing.
What I get at home with the Crown is tight deep bass and extension similar to the Krell (and boulder)- but it is not quite as tuneful as the Krell with the caveat that the Krell can sound single note on occasion when playing hard. I think it is the high damping power - I am thinking that the back emf is about the same scale as the driving voltage since the diaphragm is so stiff. So 1000 damping factor is more useful for the bass panels than it would normally be. The Crown 5000 are about 70 lb and have little bias current. Trying to equate class A to an equivalent effective power on an AB amp driving a panel I think you have roughly a 2:1 ratio so at 8 ohms a 500W class A would be equivalent to a 1kw AB in bass panel performance. Which is roughly where the Crown 5002 stands. And the Apogee/Krell bass is close to what I get with the Tympani/Crown.
If you remember the JGH review of the KLH9 then his response to having the mids and bass come off the panel rather than go to a box woofer describes well what the panels sound like when driven by an ample amp vs. one that sags.
I would suggest that you should expect to match the power supply rating of the A51 to that of the particular Crown model you are considering and remember that you can bridge the crown for 4 ohms and that on the 3600 you can do a regular bridge and there is a parallel bridge option for 1 ohm if you ever need that.
You are probably ok with the 2400/2402, if not in stereo then bridged mono, and if you want to have extra power then the 3600/3602.
I looked at some on Ebay -- they all looked pretty beat up, as if they'd been on the road . . .
That is because that is where most of them went/are. The 2400 are common small venue amps. So have the highest likelihood of having been lugged around the country in vans with less than professional care.
Finding them in presentable condition is more difficult. I got my 5002 essentially new from a cancelled concert tour.
They have been out of production for a few years now so the search will get you many a beat up but working piece. But what I stumbled upon is not possible because they are not new any longer. Do any of the new Macrotech i series amps show up?
I see a 5000i but it's $1600. And much more amp than I need! Other larger Maorotech i's for even more money. OTOH, I just found a refurbished 2402 for $550 that looks to be in reasonable shape:
http://www.ebay.com/itm/CROWN-MACRO-TECH-2402-MA-2402-GMA-2402-2-CH-1050WPC-PRO-POWER-AMPLIFIER-AMP-/361850324652#viTabs_0
FWIW as a price reference I followed eBay Macro-Tech prices for a few months.
Used not under warranty 5000i lows ran from $1,600 to $2,700.
The lowest used 9000i was $1,850 and still under warranty.
I bought one new 5000i from PlanetDJ for $2,236.76 on a Black Friday sale and another new 5000i on eBay for $2,100.00 (came with plug for South Africa :|). The normal best new online pro store prices I found run from $4,300 to $4,600.
You can email crown support a serial number and they will give you the year of manufacture and tell you if it's still under warranty.
The dsp versions, I-Tech 5000HD, record hours used. Forum wonks advise not to get earlier models not ending in 'HD'.
Thanks, useful information. I think the 5000i is overkill for my application -- I don't need all that power -- but I found a refurbished 2402 for $550:
http://www.ebay.com/itm/CROWN-MACRO-TECH-2402-MA-2402-GMA-2402-2-CH-1050WPC-PRO-POWER-AMPLIFIER-AMP-/361850324652#viTabs_0
Think that's reasonable?
That isn't a bad price but it isn't a "deal" either.
Didn't realize you could get a 5000i for that kind of money. I heard good things about their performance at the mids and top end but have not tried them myself. The 5002 I have are not that great on top.
Zulugone, do you have a comment on midrange and treble and imaging performance of the 5000i amps?
Still scratching my head. Both the Neo-8's and tweeters can get by with a smaller amp, which means the A-21 really makes sense for the woofers. But then, I want to try separating the woofers, so need another reasonably-sized amp to play with (although I can just wire them together for initial experiments and keep the woofer and mid-woofers equidistant). The only reason for the second woofer amp would be to adjust timing -- I'm not sure a crossover would be a good idea since the panels aren't quite tuned as LF/HF, there's a lower bass segment in the midbass panel.
If you are dropping the idea of crossing over between the bass and midbass panels because of their complementary tuning to perform together as a single driver then you really don't need another high power amp. Your room is small enough so that it can be fully loaded with the power on hand via the A21 and there is little to be gained by powering the bass panels separately. .
In which case you don't need a high power amp but a good quality 4 channels of high bias class A/AB amps rated around the 50-100W range at 8 ohms.
Damn, could have sworn I replied to this when I saw it a few days ago.
OK, so my senility notwithstanding, the reason I need to biamp the midbass and bass is that they probably won't be equidistant.
Of course I could use a 100 watt amp to experiment with and then get a bigger one for the second bass panel if I do decide to split them. Which will depend on whether the split arrangement sounds better than my current one, which is starting to sound pretty good. I'd been eying the little Pass for the Neos . . . not sure what I'd put on the tweeter (or if it really matters, now that my ears are only good to 12 kHz).
Not really as I have little experience listening to different amps and so don't have much of a reference. I would say the Macro-Tech tends to add more detail over the XLS-2500 across the spectrum but I would guess that's just due to the power (relative to Maggie 4 ohms) which is stable to 1 ohm. It's a soft call (subjective perhaps :) ) but I notice this detail more in symphonies and less in say solo violin.
Over time I've heard more variation between recordings than anything else. I notice less 'choral-soprano-screech' with the Macro-Techs on some old favorite CDs but I also hear more bass in the background so that's hard to sort out.
I didn't investigate any of the older Crown amps. Among the discontinued series I recall the K's mentioned often for durability and home theater use partly because they have no fans.
My Macro-Tech i's are noisy running full speed on any power draw...another DIY project to fix that. I notice them when listening to quieter classical like solo guitar.
I found some useful info on a Crown forum: http://www.crownaudio.com/forums/index.php?/search/.
Thanks. I think I'd probably do what Satie is thinkingof doing -- put the amp in another room. Still, the fans are a drawback . . .
The fan within the 'audiophile' Crown Macro Reference (~ 24 years ago) was described as "its noise distracting when listening at low levels".
Read more at http://www.stereophile.com/content/crown-macro-reference-power-amplifier-lewis-lipnick#87XGZaruTj3sRYUC.99
Yes, the fan noise can be distracting. I have some tricks to take it down and got a spool of new low gauge wiring to allow me to move it to another room eventually.
How do you think the bass amps compare, though? I was easily able to hear the difference between the three I compared while feeding only the woofer -- which rather surprised me.
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