Theta Prometheus Monoblock vs Bryston 7BSST2

I was all set to buy the Bryston 7B-SST2 amps to mate to a KEF Blade (or Blade2). However, the recent review of the Theta Prometheus on Stereophile has me intrigued. I like the benefits mentioned for the class D amps over AB or A. Less power consumption, run cool, small footprint.

I heard these amps at THE NEWPORT SHOW this year and they sounded very good but I cannot really tell in a show (unless it is really bad sound). I know how the Bryston sounds and like the fact that I would have a great RELIABLE amp if I went with Bryston. My pre-amp in the SS BAT VK-42SE. I will have a 2 channel computer based system, with the PS Audio DS DAC.

Anybody using these new Theta amps care to provide feedback on your experience. I would prefer to hide any new amps in a closed audio rack because of potential damage (spills etc..)
Hi Santabarbara, I have not heard the Theta Prometheus yet, but I own and love the Rowland M925 NCore NC1200 monoblocks ($56K/pair), and have reviewed the lovely Merrill Veritas NCore NC1200 monos ($12K/pair) for Positive Feedback:

With the premise that I love the underlying NCore sound, for the very reasons of balanced musicality, power resolution, and lack of grain and distortion discussed in the Greenhill article, I suspect that Prometheus are probably capable of making wonderful music.

Prometheus appears to be different from other NCore NC1200 implementation targeting the $12K pricepoint in at least 2 major aspects...

Merrill Veritas utilize the Hypex NCore NC1200/700 switch mode power supply (SMPS). Conversely, David Reich at Theta has designed a custom linear power supply for Prometheus... Which one is "better"? I will make no assumption that a linear power supply is ineherently better than an SMPS, or viceversa. Thus... I have no idea, but they are likely to yield subtly different results from each other.

Furthermore, Merrill Veritas declare a power of 400W/8 and 800W/4, while Prometheus declares 250W/8 and 500W/4. This difference might reflect some internal design peculiarity, or perhaps simply a more conservative power rating philosophy by Theta.

Either way, if you have the opportunity, it might be worth while to evaluate both amps in your system. Merrill might be able to arrange an in home audition... Buzz him at (415) 562-4434. Perhaps Theta or one of its dealers can do a similar thing for the intriguing Prometheus.

Regards, Guido
If you have the opportunity I would suggest checking out the new Bel Canto REF600M mono amps. They also use the nCore output stage with a custom designed input circuit and list for $2,495 each. Rated at 300wpc into 8 ohms and 600wpc into 4. There are some big claims being made for the sound quality of these amps by the manufacturer as their best sounding amps yet. Could be worth an audition!
I concur with Bill, Bel Canto has a superb track record with class D amps. Their older REF1000 Mk.2 was an absolute sonic jewel at an attractive price.

REF600 is not based on NCore NC1200 like Veritas and Prometheus, but on a yet unnamed NCore trickle-down module.... Sorry, I am still trying to find out some details....

REF600 utilizes an apparently standard Hypex NC1200/700 SMPS in each chassis. One thing unique about REF600 is that John Stronczer -- the designer -- has implemented a custom differentially balanced input stage to lower noise floor, raise common mode rejection ratio, and raise input impedance to 200KOhms.... I have not heard this amp yet, but outwardly it does look intriguing.

Thanks for your fantastic response. I had read your review about a month ago and I was looking for someone to do a comparison of the Veritas with the Theta. I cannot do this since I do not have my complete system yet (amp and speakers missing). How about you taking on the challenge? Your writing is excellent. Seems Veritas is keen for someone to do this,

"I would be happy to provide a pair of the Merrill Audio VERITAS Monoblocks for the comparison. I have also offered Stereophile the Merrill Audio VERITAS Monoblocks for review.

Perhaps there could be an independent, neutral place where the A/B comparison is done side by side. I understand some have done the side by side comparison and hope they will share their findings."

The above quote was posted on the Stereophile web site on the Theta review.

It would be great if Theta is interested in this comparison.
These great response have me spending my day researching the Veritas amps. Here are some links that some reading this thread may appreciate.
Hi YYZSantabarbara, a comparison of Veritas and Prometheus would make interesting reading....

But it is more likely that you will continue to find reviews that are targeting one product at a time.... You might need to continue drawing your own comparisons by unscientifically reading between the lines... Particularly tricky if the two articles are written by two different reviewers.

I have a dealer who loaned me these amps for a week to
use in my own system. It was rather cool to read the
Stereophile review after already having listened to these
amps. They replaced a Mark Levinson 335. By coincidence
the reviewer's amp is the ML 334. Similar voicing as the
No.335 but less power. I must say that I am in love with
the low end, the dynamics, the wide open soundstaging,
and layers of detail within that same soundstage that are
now present. The sometimes slightly dark sounding
midrange that the 3 series has on some systems is gone. I
ended up buying the amplifiers! The amps I had in
my system to listen to for several days prior to the
Prometheus were the D'Agostino Momentum monoblocks. No
way I could afford five of those! I had a good comparison
to make my decision.
Hi Statman, which dealer did you work with during your successful Prometheous quest?

Saluti, GUido
Statman, if money was no object, would you prefer the Thetas vs. the D'agostino Momentum? I have read the latter has a veil over the sound compared to the more transparent amps...
+1 on the BeCanto REF600M.

Yyzsantabarbara hi.

The Kef Blade II are hard but not too hard a load to drive at 87db and 3ohm min right across the low to mid bass. And there are no nasty - phase angles to worry about.

So a very good 4ohm capable amp would do, I myself would be looking at Pass Labs XA class of amps.

I do not think class D has come of age yet, as the switching frequency technology is not yet high enough.

Another amp worth looking at is the Parasound Halo JC1 mono-blocks in their higher Class A mode that's switchable on the back, I listened to these on a pair of Wilson Alexia's, a real evil load (.8ohm epdr), and they sounded great with this amp.

Cheers George
"I do not think class D has come of age yet, as the switching frequency technology is not yet high enough"

George, which amps have you experienced which are the audible cause of your pessimism?

I didn't consider the D" Agostino amps "veiled" at all. The actually "bloom" in the midrange, giving it a somewhat "tube like" sound in the mids and highs. Plenty of power and low end to spare. They just cost way too much for an application as mine.
I am looking now looking at new technology for these speakers, no A or AB amp designs. The amps I am now going to audition are, Merrill Audio Veritas, the Theta, Benchmark AHB2, Bel Canto REF600, or the Devialet 400.

I am buying the Benchmark AHB2 very soon for my office system, Benchmark DAC2 and KEF LS50 speakers. These amps are strong enough to power a line of speakers I have owned in the past, Revel Salon. They are being demoed at some shows with this combo. So this amp will be tested first with the Benchmark DAC2 on the new main system I am building. Maybe it will surprise me.

My main concern now is deciding whether to go direct to the amps from the second DAC I will get (another Benchmark DAC2 or PS Audio DS). I have my pre-amp for sale but I am thinking that maybe a bad idea and I will regret selling it.

The Devialet is another system that intrigues me and the place that I will buy the Blades, Audio High in Mountain View,CA, also sell this system. They demo the Blades with very expensive Chord electronics. Which I heard but I am not interested in spending that much money for electronics.
Hi YYZ, the Bel Canto Ref500 monos are based on the somewhat less powerful NC500 module, instead of the NC1200 used in Veritas and Prometheus. As a result, the peak current of Ref600 is 27A instead of 38A. I suspect you might find REF600 to have less authority than Veritas or Prometheus, and perhaps a little bit less resolution.

Keep us posted on your listening experiences!

Regards, G.
YYZ, I have owned the Veritas since it was first introduced. Below are some thoughts and suggestions.

1) I have demoed many amps in and out of my system. IMHO the Veritas punches way above its price point.

2) NO amp is perfect or ideal for everyone. We all hear a little differently and have different tastes.

3) I had Merrill Audio replace the fuses in my Veritas with the new Synergistic Research Red fuses. All I can say is DO IT!! I second thought, DO IT ON ALL YOUR EQUIPMENT.
I have tried many fuses and while a few made a slight improvement (many did not) the RED fuse is amazing for just a fuse. While you must have the fuses in the Veritas replaced by the factory any fuses that are DIY can take advantage to the 30 day free trial that Synergistic offers.

4) I owned the Bryston 14B SST2 amp. It is the stereo version of the 7B SST2 mono that you mention above. Only difference is one case vs two.
it is a really nice amp and sounds good.
But IMHO the Veritas sounds better.

5) I agree with Guido. Just because an amp uses either a SMPS or a linear power supply does not dictate how well it will sound.

6) Whatever amp you get I would highly recommend that you use Stillpoint footers. And if you can afford it get the Ultra SS. The Ultra Mini is worthwhile but the Ultra SS is better. You can use three vs four in most cases.
And if your budget allows use the Ultra SS on your speakers. Depending on your budget Use the Ultra Mini on your amp/s and the Ultra SS on your speakers. Even if your speakers use spikes.

Regardless what amp you get I wish you good luck and happy listening.

PS Hey Guido. I hope all is well.

Hey Al, things are good.... Absolutely adore my big rig with Rowland Aeris DAC and M925 monos....

Yet, at its uber-attractive pricepoint, the little Taranis stereo with gain raised to 29dB was a real treat on my Vienna Die Muzik speakers.

For the rest, believe it or not... I am having immense fun fiddling with high brass instruments and mouthpieces.... Adams A4 Heavy trumpet, Kanstul 1525 copper flugelhorn, and very recently Carolbrass CCR-7772R 3-crooks Bb cornet and CCR-7775 Eb soprano cornet... Nuts am I? For sure!

Not that it makes much difference to this discussion but the Bryston 14B amp is not 2 x 7B in one chassis. They differ in capacitance as the 14B has 108,000MFD per channel and each 7B has 160,000MFD so the 7B amps offer 48% more capacitance in each channel....
Rgd, that may be but the owner of Bryston himself told me what I wrote in the above post. So ...

"George, which amps have you experienced which are the audible cause of your pessimism?"

Many and they all have the same trait, explained below.

Until the future technology gives us higher switching frequency, we'll get this (linked) switching frequency noise on the top of the square wave in pic 2 and that's at 1khz!!!
At 10khz (not shown) it's 10 x worse (if this was a linear amp, you'd say it was broken)
And the output filter is already started to roll the audio frequency off at 10khz to try to minimize it Pic 1.

Today we have two detrimental ways to get rid of the Class D switching noise, with output filters on these amps.

1: The filter to roll off earlier into the audio band to minimise the noise, result (soft/opaque/dark treble and upper mids and hf phase shifts)

2: The filter to roll off later with no treble roll off and minimized hf phase shift, but let 10 x the switching noise through (hard in your face treble and upper mids).

Or we bite the bullet and use Class D just for bass, and wait for technology to advance to get much high switching frequencies for class D so we can then filter them out much higher and more aggressively with being near the audio band.
It will happen one day and that's when I will get one as well, but today it is just not ready yet, it's still developing, when it does our heavy massive linear amps will become boat good anchors.

Cheers George
George, are you saying that you audition graphs, and faithfully follow those pundits who seem to suffer from Princess And The Class-D Pea syndrome?

Your implicit trust in the press is admirable... It spares you from the unavoidable surprises of audible reality


No, you asked me what I listened to, cause of my pessimism.

And I said "many" and they all have the same trait/s.
And then I gave reasons "cause" to why I hear this.
One day they will come of age, then I will own one.
You choose not believe? I can't help that.

Cheers George
We ALL just need to believe one guy more than our ears.

Designers and fans of digital amps - Theta, Veritas, Bel Canto, Rowland, etc - who cares?
They all don't hear so well, no?

3 words come to mind - dogma, dogma, dogma.
Yyzsantabarbara, I wouldn't write off Dan D'Agostino audio company yet, Dan just introduced some new more affordable model line's of amp's that are getting world wide reviews, check them out on his site, tell me what you think?
Right on Jon, my old hearing is clearly impaired *grins!*

Actually, I examine amps one brand at a time, and one model at a time.

Currently, my favorite uber amps sound comes from Acoustic Research, Brmester, Solution, and yes... Rowland. Any of these brands have some machines that make enchanting music to my ears.

Class D has the same potential for good and bad sound as any other base topology... It all depends on componentry, goals, design, and implementation. All other things being equal, The common advantage of Class D over other topologies remains energy efficiency, hence minimum cost of operation.

Is class D inherently great? Heck no! I have heard certain current class D amps sounding positively acrid... Best used in attics.... They chase Roaches and other critters away for pennies a day. But so do some much vaunted class A/B devices, and more than a handful of tube amps... At a higher operating cost, that is *grins!*

Bottom line... Generalizations are a slippery business.

For pennies a day? If Class D amps come any cheaper, we can stop paying those pestbusters. Now, THOSE guys really don't come cheap. :)
Hmmm... I was really thinking about the miniscule AC bill... The initial capital investment remains... Uhrn... Audiophrenic madness *grins!*
Hey, AL,

You are back. How are things over at your Tara Labs thread?
The new "trickle-down" D'agostino stereo amp looks gorgeous.
Cheers! J.
For anyone who is interested the latest issue of Stereophile has a review of the Benchmark AHB2 amp that I am getting for the office system. It sounds like a real sleeper amp.
yyzsantabarbara, I'm about one year behind you but going down the same path. What did you discover about the Prometheus/Blade2 combination?