2. amps-preamps
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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..)
yyzsantabarbara

Showing 3 responses by georgehifi

georgehifi's avatar
georgehifi
10,312 posts
 

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
georgehifi's avatar
georgehifi
10,312 posts
 

"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.

http://www.stereophile.com/content/theta-digital-prometheus-monoblock-power-amplifier-measurements#d5BMlUSvHXmmeEbA.97

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
georgehifi's avatar
georgehifi
10,312 posts
 

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
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