DEVIALET POWER AMP, Will there ever be a power amp...

[ogs]

Even if a Devialet power amp is possible, and technically I think it is,  I agree with @Damon that the current 'complete' design is the best solution. If one really wants/needs separate components the Benchmark AHB2 power amplifier is very good sounding and even cheap. Good starting point for a system with separate components.

[chrisc]

Good article, if quite scientific about the US patent awarded to Devialet in 2004 for the ADH concept. Quite a lot of maths

The Abstract:

An amplifier includes an output for feeding a load, a voltage generator presenting very high linearity and very low output impedance, and a current source having its output connected to the output of the voltage generator at a coupling point connected to the output. The output of the voltage generator is connected directly to the coupling point without any resistive element being interposed between them. A control stage controls the current source from the current delivered by the voltage generator. The control stage for controlling the current source includes current measurement elements for measuring the current delivered by the voltage generator, and the elements are disposed solely upstream from the output for feeding the load.

https://patents.google.com/patent/US7545212B2/en

[thumb5]

Maybe I'm missing something obvious to others, but here goes anyway: what would be the difference between a Devialet power amp and an existing Expert (Pro) driven by its analog line input? A lot of other input sources missing, of course, so is this simply a request for a cut-down Expert without those input sources?

[ogs]

AFAIK the input to the power stage in ADH is analog i.e. after the 'Magic Wire' DAC. The line in on an Expert amplifier goes through AD conversion for processing (volume control, tone.... etc) and then the 'Magic Wire' DAC.
What would make a separate ADH power amp difficult (or indeed impossible) is that I believe DSP is used to control many functions in the power supply (like DMP) so the DSP depends on the audio stream going through to make correct calculations. It would, as @thumb5 says, just be a cut-down Expert amplifier.

[chrisc]

Yes, ogs is 100% correct. Every input goes via an AD conversion process. This seems to upset some people as they think it diverts away from the "purist" principle. The AD is done at 24bit 192KHz

There is obviously much more to the process than AD and DA, but Devialet have managed the design so elegantly that the result is superb

Our audio club here in Cape Town have compared the sound from the line in on a Devialet 220 Pro CI with a Krell, a Trigon, a Jeff Rowland 725, PassLabs X600. The Jeff Rowland was thought to offer an edge, but more than 3 times the price

[David A]

… Every input goes via an AD conversion process.… The AD is done at 24bit 192KHz
…

The first statement is obviously incorrect and I don't think that is quite correct.

Not all inputs go via an AD conversion process. Digital inputs are already digital so can't be converted from analog to digital and they don't go through any AD conversion process. That's the obvious wrong statement and I'm sure you meant to say "Every analogue input" but missing out the word "analogue" turns what would be a correct statement into a very incorrect one.

Now to the second statement. The highest resolution digital input an Expert Pro can accept is 24 bit 192 kHz but my understanding is that all digital inputs are actually upscaled to a higher resolution for the DSP operations the amp does. If I remember correctly, the Expert Pro uses a 30 or 32 bit 384 kHz data stream internally so all AD conversions would be done at that resolution and all digital input signals would be upscaled to that resolution.

As you say, the result is superb.

[ogs]

I've read or heard a long time ago that Experts have 40bit to work with. I am not so sure about 384kHz. Maybe dual-mono upsamples to 384, but I think a stereo amp is 192kHz. I asked Devialet support about this several years ago (2015) and they said this:

"Dear Sir,

Thank you for your patience.

As you understand, a Devialet 400 is composed of two units of Devialet 200.
The Devialet 200 can upsample to 192kHz. So with a 400 (2x 200) you get a signal up sampled to 2x 192, meaning 384khz.

So, 384kHz over-sampling is not used in 120 or 200, but it is possible with Devialet 400 and 800."

I guess this indicates that at least the 440 and 1000 can upsample to 384kHz.

[chrisc]

Yes, the statement is better expressed as "analogue inputs". I thought that would have been self-evident

[David A]

Yes, the statement is better expressed as "analogue inputs".  I thought that would have been self-evident

It probably is self evident to many people but I spent too much time in the Philosophy department when I did my undergraduate degree and I became accustomed to taking people at their word, precisely at their word, because my lecturers had a habit of taking me at my word, precisely at my word.

Most people would have assumed you meant analogue inputs and, as I said, I thought you meant that. Some people, however, may not be clear about all aspects of digital audio processing about just how a Devialet works. They may assume that when someone says"all inputs" they really do mean ALL inputs.

[David A]

I've read or heard a long time ago that Experts have 40bit to work with. I am not so sure about 384kHz. Maybe dual-mono upsamples to 384, but I think a stereo amp is 192kHz. I asked Devialet support about this several years ago (2015) and they said this:

"Dear Sir,

Thank you for your patience.

As you understand, a Devialet 400 is composed of two units of Devialet 200.
The Devialet 200 can upsample to 192kHz. So with a 400 (2x 200) you get a signal up sampled to 2x 192, meaning 384khz.

So, 384kHz over-sampling is not used in 120 or 200, but it is possible with Devialet 400 and 800."

I guess this indicates that at least the 440 and 1000 can upsample to 384kHz.

@ogs,

I've only had my Devialet since 2017 so I'm unfamiliar with what they were saying in 2015. I had always assumed that the DAC and DSP in the Devialet operated at 24/192 but then I saw someone on this forum say that the DAC and DSP operated at a higher resolution and I came across a link to a white paper on Devialet's site where they went into some detail on how the Expert Pros did their digital processing and it confirmed the statement I had originally read. I just tried to find the page on Devialet's site which provided that information but I can't find it on the site with their current menus. I did come away thinking it applied to all amps, both the single and the dual amps but memory being what it is, I could be mistaken though I do believe that all current models, not only the dual amp models, do handle all of their processing at a higher rate than 24/192.