The official "Theta" thread - Page 52

Of course 11.1 channels is a great idea, esp if you manufacture amplifiers. Yippee.

I have just heard through a source totally unrelated to this forum, that a prototype of a USB to s/pdif converter exists.

I asked if he could reconfirm with his contact the information he relayed to me concerning this converter but that may take sometime.

Any idea if this might be true?

We already know that Berkely has come out with a super duper high quality asynchronous USB to s/pdif converter, MSRP $1695, just becoming available. With both coaxial and AES/EBU digital outputs. So should work great for both CB3 HD and Gen VIII Series 3 DAC!

Or are you trying to tell us Theta is workin' on such a beast?


By the way, watching Hall and Oates Live at the Troubador. Darn it sounds outstanding, as well as the concert video footage is also top shelf.
I'm tellin' you blu ray concerts and music are awesome in this super Theta system!

That's exactly what I was trying to say.
I was told that a Prototype might exist as we speak.

Hall and Oates?

Just kidding. I have plenty of guilty pleasures on Blu Ray (Rush Snakes and Arrows comes to mind).

Im glad Theta is back in a big way. I owned them a few years back, but was talked into switching to another manufacturer when Theta seemed to be in trouble. I think I will give them another try. I have some questions for you guys about Theta.

1) How much influence does ATI have on Theta. My concern would be that A DNIII would be mainly an ATI influenced amp, while the DNII would be the classic Theta sound and design. What do you guys think about this.

2) Also, I have some questions about some of the reviews reviewers have given some Theta amps. Mostly the measurements they find that they attribute to the lack of negative feedback. For example, Stereophile claimed of the Intrepid on page 2 of their measurements . . .


The THD seemed to be in a 3rd harmonic only, and the reviewer said the amp sounded very good despite the THD measurements. I know the Intrepid is discontinued and a budget item, but in the review of the DNII, Ultimate AV claims in their measurements of the amp . . .


The DNII is supposed to be 225 per channel into 8ohms, and about 500 into 4ohms, but the measurement says the THD is 1% at 192 watts and 228 watts? I owned this amp, and thought is sounded great, blowing away the competition but these numbers don't make any sense. TJ Nelson reviewed the amp for Ultimate AV and said it sounded great too. The DNII is also discontinued, but the Enterprise is not. Stereophile reviewed the Enterprise, and we all know that the review isn't useful, but the measurements seem to show lots of THD too. Their review measurments show . . .


Again, I know the amp sounds great, but what can be made of the high THD? Even the mighty Citadel suffers the same measurements. Stereophile measured the following in their review . . .


But the reviewer raved about the amp, and the reviewer at Ultimate AV bought the amps and said they were the best he had ever heard.

Can someone please sort out the odd measurements and how they can be there yet the amps sound very good. My main concern is about the amp clipping (defined as 1% THD+noise) and damaging the speakers.

Thanks.

If you can survive with a couple hundred watts of clean power, you'll have no problem hearing clean sound and avoid any clipping whatsoever into the speakers. The only time the amp clips at 1% or 2% is when overdriven. It is useful to know where that point is for comparing with others, but it's irrelevant as an indicator of sound quality.

None of the measurements quoted reflect the distortion under listening conditions.

That is what I was thinking. The reviewer seemed to be confused as to how to measure the amps with their devices, due to the 0 feedback and the lack of a common ground for all channels.

ATI owns Theta, ATI is Theta. Just like ATI owns B&K. ATI is B&K. So ATI's owner Morris Kessler makes the final calls on everything. Morris invested a lotta bucks in the CB3 HD upgrade that hardly any of us, including me, would actually ever come to fruition,and it it did come to fruition, would sound like it should (great) and work functionally. But the upgrade has been very successful and the orders for upgrades and new units have far exceeded expectations in this dismal economic climate. So much that President Obama may include taxation of those who can afford Theta products along with corporate jets in his next speech on taxes and the economy.

You can credit Morris and his ATI team,working with Dave Reich, President of Theta Digital, to come up with the humungous toroid power supply in the CB3 HD that makes it sound better than ever even on redbook PCM and Dolby Digital!!!@@@

ATI owning Theta isa big plus! Theta's prior owner, Neil Sinclair, sold to ATI purposely, instead of say to Chinese or other contenders, not only for the money, but also because he felt ATI had the best chance of continuing Theta along the audiophile and great sounding way that Neil had taken the company. Looks like ATI is taking us for a nice ride into a great sounding future!

Theta amps have feedback.

Re grounding, one should never ground any speaker terminal of a power amp, even if it is nominally at ground. So there's nothing special about measuring a Theta amp in that respect.

Is the review to which you refer posted somewhere?

I was told that Jeff Hipps is big on room correction. From a marketing perspective, that is the Achilles' heel of the Casablanca. Thanks for the tip about 11.1. It is likely that I will be building a new home. That will be kept in mind when I start construction. My surrounds are in-walls speakers now. With that many channels, I am going to have to stick with them. Adding something on the ceiling seems obvious but I will have to investigate the likely locations for the other channels.

David Reich designed the Dreadnaught III. Do you hire one of the more herald amplifier designers of the last couple of decades to have him not design your amps? I do not think ATI will do that.

The newer amp the DNIII has new transistors. Thermal tracking transistors allow for more precise bias tracking. Amp design has not changed much in many years. The Thermal Track transistors are an improvement I want. Several high-end companies are using them including Ayre who's designer did most of the work on the original Dreadnaught when he worked for Theta.

You would have to hear both amps. The change in design and transistors will change the sound. I use Mcintosh amps which also uses the Thermal Track transistors. So far, the newer designs from the various companies are preferred to the older designs without them.

Thanks! I found this http://www.dts.com/Corporate/Press_R..._at_CeBIT.aspx I will have to hear this to see if it is worthwhile. What is the DTS room correction system called?

From the demo I heard earlier this year at CES, it is worthwhile. The height effect seemed particularly effective, but we may have been listening to demo material encoded with height info. I'm not 100% sure, but I think the MDS chipset in the CB3HD should be able to run Neo:X (and DTS room correction, since they use the same filter banks).
At this point, speaker locations for the other channels have been somewhat standardized (informally). Centre at zero degrees, Fronts at +/-30º, Wides at +/-60º, sides at +/-90º degrees, rears at +/-150º. Heights go high up above the Fronts, or spread slightly wider (+/-45º) if you're not using wides.

Re. the Feedback: Theta amps have no global negative feedback. That is why I placed a zero in front of the word feedback. Zero Negative Feedback.

Re. Grounding: the reviewer claimed concerning grounding in his measuring of the Intrepid . . .

This is what I meant concerning the grounding issue. The reviewer had to use a different measuring device because his normal one connects the negative to ground.

Re. the availability, all the reviews and measurements are available online and that is why I referenced the publication, the item reviewed, and the page for each comment I posted.

Thanks

But what you wrote was "0 feedback" which is not accurate. Nor is it accurate to say "Zero Negative Feedback." Theta amps do have negative feedback -- local. What they do not have is global feedback.


Yes, that's not a problem only for Theta, but for every amp he tests, if his normal rig is actually connecting speaker terminals to ground.


I was asking about this quote:
Which review is that from?

I do not know. It is described in this AES paper.

Roger, all my posts have been in the spirit of me trying to learn from the guys on this forum. If you want to address my initial QUESTIONS please do, but I don't want to have a back and forth over a reviewers comments. With that being said, the following are my thoughts on your questions.

1) Regarding the feedback issue, Im not trying to make a point about the amount of global or local negative feedback that Theta uses. My point was to address the fact that each review I quoted has the reviewer pointing out that the way Theta has set up their feedback makes the measurements different from other amps with respect to THD + N. I was saying that perhaps this is why the reviewer's measurements were interesting to them. Regarding my claim "Zero Negative Feedback", I was not incorrect as much as I did not think the amount of specificity you expected was warranted. I assumed we knew it was local and not global, and that the amount of negative feedback applied locally is so low that it is essentially near zero. After all, Theta themselves do print "Zero Feedback High-Current Amplifier" on the Citadel 1.5, and on the Enterprise, which is no more or less correct than my claim, but it is less precise then my words and less precise than your expectations. If you disagree with my wording, you also disagree with theirs.

PS . . . Stereophile's measurements of the Enterprise references the negative feedback four times.

2) Regarding the ground issue, your disagreement is with the reviewer of the Intrepid, not with me. He claims that the Theta amp could not be used with the Miller Audio Research Amplifier Profiler because it connects the negative to ground, but other amps didnt have this limitation. The reviewer of the Enterprises said the grounding of the Enterprises and the Citadel was different from other amps which do have a common ground. Their words, not mine. Again, these can be found online.

3) Regarding the question about the review, this was from the 4 reviews I commented on. Some reviewers commented on the grounding, while others commented on the feedback.

Yes, I do. Precision is worth while. Too many people pick up on the marketing blurb literally, and thus carry misconceptions and spread them on fora like this. That you are not confused is good to know. But these threads are read, presumably, by a lot of others who may not be so well versed as yourself.


Then it should not be hard to represent the facts accurately.


Of course! I hope that was obvious.


Other amps might not have exhibited as strong a reaction, but the Miller device is poorly designed if it grounds the speaker terminals. No speaker does that, so why should the test equipment operate under different conditions? Yes, it's a rhetorical question.


Yes, 4 reviews. I looked through some of the reviews but did not find grounding issues mentioned, and figured since you read them all and knew exactly which one you were quoting, it would not too hard to simply post the link. Sorry to have been a burden.

The grounding issues relate to the issues the reviewer's seemed to have in their measurements with the amps, not to the operation of the amps themselves. My noting them was in response to another comment, and was meant to say that perhaps the reviewer was at fault for the results of the measurements because they may not have known what to do with the Theta design. Thats all I meant. I found 2, one in the review of the intrepid, which I posted in its entirety previously, and the other in the measurements portion of the Enterprise review. Here they are again.

John Atkinson's measurments of the Intrepid - http://www.stereophile.com/content/t...rements-part-2
Michael Fremer's review of the Enterprise - http://www.stereophile.com/solidpowe...ta/index4.html
It just seemed that whatever reason they were not anticipating the Theta to be configured this way. I know not why. That is all I meant.

Thanks. It may not be DTS they use. Still a ways off I am sure. I believe I have a clue as which company they are considering.

Exactly! This was never in doubt.


Exactly!


Much obliged.


The burden is on the product testers to use the right gear and procedures so as to not introduce invalid operating conditions. Mr. Atkinson wrote: >>As both positive and negative speaker terminals are actively driven, the Theta could not be tested with the Miller Audio Research Amplifier Profiler, which connects the negative terminal to ground. However, using the Audio Precision System One, which has floating inputs<< which is an excellent conclusion, as far as it goes. He should use the AP for all amplifier tests.

Roger, isn't it the norm, rather than the exception, that any "high-end" power amp's negative speaker terminal is NOT at ground? I wrote "high-end" because I think some Japanese receivers might have theirs at ground.

Events were a long time ago & not my field of expertise, so I don't remember the exact details, but in college I had one of those Radioshack "power meters" with 2 rows of (exciting!) flashing led lights, indicating power output in wattage. Although this had worked fine w/ the Kenwood amp I had at the time, many years later when I tried to use this meter with a "high-end" amp (either Aragon, or Krell, or Audio Research, don't remember which), I remember that it caused some problem - blown fuse or amp turning off - that was attributed possibly to the meter grounding the 2 neg terminals of the amp.

I have looked at schematics for Krell, Classe, and Bryston, and while it's a small sampling, they are all conventional in that the negative terminal is at nominal ground. But even when it looks like it is at ground on a schematic, does not mean it is OK to tie it to ground. That can create a ground loop thru the amp.

Not sure what goes on in the Theta amps that makes them particularly sensitive, but IMHO it is no failing of the amp if it does not like being dragged to ground.

Bridging amps of course drive both output terminals, but I don't see that happening unless by external connection option.


Most, if not all.

If Jeff Hipps has anything to say about it, I can make a wild guess.

Bulldogger,

For many people, the lack of room correction is not just a marketing Achilles heel. As you know, there are very valid objective and subjective (e.g. the ability to adjust the curve to taste) reasons for the addition of room correction. I think many people will find a proper implementation of the tool (and its application in room) to the CB3 HD to be a wonderful addition.

Has Jeff Hipps not expressed a liking for the Trinnov in the past?

Yes, and rightly so.

If Theta is going to do room correction hopefully it will be in the form of a seperate box like this http://www.ada.net/products/ht/teq_trinnov.php. Hopefully it can be designed to accept a digital output from the CB3HD

Not a chance. First, they would need a HD digi out card before going this route. Second, this would restrict the solution to users with external GenVIII's, unless you could loop the digitally corrected signal back into the CBIII for conversion with the Theta DAC cards, which would require more new hardware. This would be an extremely unlikely architecture. Room EQ will be added on board of the CBIII HD.