Theta Digital Prometheus monoblock power amplifier Specifications

Sidebar 1: Specifications

Description: Solid-state monoblock power amplifier. Inputs: single-ended (RCA), balanced (XLR). Outputs: 2 pairs Cardas binding posts. Output power (20Hz–20kHz, 0.01% THD+N): 250W into 8 ohms (24dBW), 500W into 4 ohms (24dBW), 850W into 2 ohms (23.24dBW). Frequency response: 20Hz–20kHz at 300Wpc, +0/–0.5dB. Input impedance: 47k ohms. Output impedance: 0.05 ohm, 20Hz–20kHz. Damping factor: 2500 (minimum), 20Hz–20kHz. Input sensitivity: 130mV for 2.83V output, 1.825V for full output. Signal/noise: 124dB, A-weighted. Voltage gain: 27.8dB. Power consumption: 1W at standby, <40W idle, 1200W driven maximum (950W into 2 ohms).
Dimensions: 13.5" (346mm) H by 9" (230mm) W by 19.8" (508mm) D. Weight: 54.5 lbs (24.8kg) net, 64 lbs (29.1kg) shipping.
Finishes: Platinum, Ebony.
Serial numbers of units reviewed: 050085 (L), 050021 (R).
Price: $6000 each. Approximate number of dealers: 57. Warranty: 5 years, transferrable.
Manufacturer: Theta Digital/ATI, 1749 Chapin Road, Montebello, CA 90640. Tel: (323) 278-0001. Fax: (323) 278-0083. Web:

Theta Digital/ATI
1749 Chapin Road
Montebello, CA 90640
(323) 278-0001

remlab's picture

..and I think he is a genius, but when all these companies are using the same basic modules(I think that Jeff Rowland uses it also), aren't they all building pretty much the same basic amp?

dce22's picture

sys2722 has AES17 filters use those to test Class D amps stop using AUX-0025 on AP2.
Theta Digital Prometheus Distortion 0.01 at 15 watts?
Is that a joke? John Fix Your Measurements Chain!
I have tested alot of ICE power amps and Stereophile data always has more than 10x distortion than the real world data.
AP1 and AP2 inputs will not distort from switching residual only the Autorange circut will trigger wrong scale and you use AES17 filter to fix that, and for frequency response you do not use filters of any kind only Distortion Measurments needs AES17.

PS. IM graph is not correct and Freq Response is from the AUX-0025 not the amp.

John Atkinson's picture
Thank you for your comments, especially concerning the auto ranging. I have tried measuring both with and without the AES17 brick wall filters. The frequency response is genuine, BTW, and is not due to the AUX0025.

John Atkinson
Editor, Stereophile

dce22's picture

John i did a prototype with NC1200 modules and got identical graph as Hypex datasheet i dont use AUX0025 at all only AES17 the switching residual will not induce slew rate distortion (unless it has so badly design filter that will not pass FCC regulation), maybe Theta Digital has that bad input stage that adds high frequency distortion, noise and roll off ill try to borrow one to test it.
The distortion nubmers on 4 ohm are terrible for this kind of amp maybe the power supply transformer is too small and the noise performance is crap.
I can upload images but they are the same as the official datasheet. Cheers J.

PS. I need to mention for non technical audiophiles when using AES17 filter distortion data are only valid up to 6 khz because AES17 filter is a 20khz filter design to measure Sigma Delta DAC's, from 6 - 50khz is covered by 19+20kHz Intermod distortion measurments (you can use 19+20khz IMD data as equivalent to 20khz sine wave distorion measurments only instead of looking at the spectrum above 20k the distorion commponents will mirror back inside the audio band and you can use 20khz bandwidth for less noise there is no need to use some new "super hyper oscilloscope" thats the beauty of it) and switching residual is not somekind of wierd noise, it looks like a parabolic shapes up and down string together something like sinewave but with parabolic halfs and is in milivolts the tweeters are up to hundreds of ohms at 400khz cant even fell anything let alone distort so no worries.
When you Measure the amp with AP2 and you start at microvolts the Autorange circut will see mili volts and yell to his buddy DSP hey there is voltage comming get going change the scale! and the low level data is not usefull, there is no distortion no wierd thing going on people need to relax AP recommends AUX passive filter because there is a nutjobs that run Class D without filters and try to measure it that way that amp my frends is broken, that can be a good test for John if it need AUX-0025 That amp is Broken :) and AP1 needs AUX-0025 because it does not have proper AES17 module slot. I forgot to trasmit 400khz you need 750 meters of speaker cable so dont worry about RF offcourse there are horrible designs that wipeout all the radio staions in the area but it is not because off the speakers cable emmits at 400khz its because amp pushes Mhz's into it, amps modules like B&O Ice power and Hypex have non of the problems.

dmusoke's picture

John.. thanks for the detailed review. Its nice to know that Class D technology has matured to the point of being considered in high end audiophile amplifiers. I have one concern in your measurements, but by placing an external 20kHz filter that doesn't exist in real life, you make the measurements of the amplifier look better than they should be. The effect of these high energy ultra-sonics on the distortion numbers is masked. What effect would they have on actual loudspeaker systems? Why not make the measurements with the default 80kHz bandwidth of the AP test system?

John Atkinson's picture
Why not make the measurements with the default 80kHz bandwidth of the AP test system?

First, because with hundreds of millivolts of ultrasonic noise present, any THD+Noise measurement will be dominated by that noise, even with the 80kHz measurement bandwidth. Second, that ultrasonic noise will drive the AP's input stage into slew-rate limiting, generating additional distortion.

John Atkinson
Editor, Stereophile

dmusoke's picture

So should we have no concerns for these ultra sonics on our loudspeaker systems or radiated emissions to other electronics in our AV systems? BTW, what is the frequency of this ultrasonic noise, which I presume would be the switching frequency of the amplifier?

John Atkinson's picture
dmusoke wrote:
So should we have no concerns for these ultra sonics on our loudspeaker systems or radiated emissions to other electronics in our AV systems?

Not necessarily. Remember that hooked up to the amplifier's class-D output stage is an antenna - the speaker cable. This, of course, is loaded by the speaker, which presents a low impedance at audio frequencies. But above 100kHz, the speaker may well present a very high impedance, due to the voice-coil inductance of the tweeter. So depending on the length of the cable and the ultrasonic impedance of the speaker, the residual switching noise may well be re-radiated into the environment, as well as finding its way into the system ground, which will depend on the amplifier design and circuit layout. All these factors are unpredictable.

dmusoke wrote:
BTW, what is the frequency of this ultrasonic noise, which I presume would be the switching frequency of the amplifier?

It tends to be between 400kHz and 500kHz.

John Atkinson
Editor, Stereophile

dmusoke's picture

I appreciate the answers John. Thank you :)

IgAK's picture

An interesting article, thank you. A comparison to the similarly priced Merrill amp using the same rather popular N-Core module would have been an interesting implementation comparison.

MerrillAudio's picture

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.

dcvibe's picture

Would love to get a non biased opinion about these two amps?