Have amplifiers finished evolving?

[Darth Vader]

Devialet work entirely digital. Analogue signal path is about 2cm at the end.

No. At the heart of their amplifier is a class A output stage For want of a better description it is a class ADH amplifier. They have replaced the class B stage for the smaller and more efficient class D switching stage. The whole point is that the quality of the output is governed by that class A stage. There is actually a DAC in front of this ADH combo thus any digital input is converted to analogue before it hits the output stage!

Personally I don't buy into the Devialet story and certainly not for loudspeakers that are stressful to power amplifiers and thus difficult to drive. I also look at pfm members who have had Devialet pass through their HiFi systems as it just doesn't meet their expectations.

For me class D power amplification is great for on the road PA systems as you get a lot of power in a small, light and cheap package. OK for discos and the like but HiFi? Class D is also great for miniaturisation such as portable devices and hearing aids where sound quality is not the main requirement.

Why don't you guys read up on this stuff before posting silly comments on a public web site? From the Devialet web site:-

"....the idea of ADH is to maintain the analogue amplifier's voltage generating function (to maintain their excellent audio performance levels), while entrusting the current generation function, and accordingly, that of generating power for the load, to an amplifier equipped with drastically superior energy efficiency: in this case a digital amplifier, otherwise known as a switch amplifier."

If you believe that marketing guff.........

Cheers,

DV

 

[sq225917]

\duh, cos it's the internet, that's what it's for.......going off half cocked and getting into asinine discussion about nomenclature are why it exists, surely?

 

[Cereal Killer]

 

[GT]

No. At the heart of their amplifier is a class A output stage For want of a better description it is a class ADH amplifier. They have replaced the class B stage for the smaller and more efficient class D switching stage. The whole point is that the quality of the output is governed by that class A stage. There is actually a DAC in front of this ADH combo thus any digital input is converted to analogue before it hits the output stage!

Personally I don't buy into the Devialet story and certainly not for loudspeakers that are stressful to power amplifiers and thus difficult to drive. I also look at pfm members who have had Devialet pass through their HiFi systems as it just doesn't meet their expectations.

For me class D power amplification is great for on the road PA systems as you get a lot of power in a small, light and cheap package. OK for discos and the like but HiFi? Class D is also great for miniaturisation such as portable devices and hearing aids where sound quality is not the main requirement.

Why don't you guys read up on this stuff before posting silly comments on a public web site? From the Devialet web site:-

"....the idea of ADH is to maintain the analogue amplifier's voltage generating function (to maintain their excellent audio performance levels), while entrusting the current generation function, and accordingly, that of generating power for the load, to an amplifier equipped with drastically superior energy efficiency: in this case a digital amplifier, otherwise known as a switch amplifier."

If you believe that marketing guff.........

Cheers,

DV

Suitably nailed!

 

[Cereal Killer]

Thing is Devialet is both, the 7w Class A analog output moves up/down with the PWM of the Class D amp section which is also the DAC and ADC. The tech is indeed rather clever.

 

[GT]

Thing is Devialet is both, the 7w Class A analog output moves up/down with the PWM of the Class D amp section which is also the DAC and ADC. The tech is indeed rather clever.

Diagram from Devialet: Note the output of the DAC feeds the Class A stage which is parallel connected to the Class D output stage, both work in tandem. I would be extremely surprised if the class A output was anything like 7 watts. There is insufficient heatsinking to dissipate the heat that would be generated by 2 x 7-watt class A amplifiers unless it was fan cooled. Apart from the ADC, DSP and DAC, the amplifier concept is very similar to what Peter Walker designed and used in his current dumping QUAD 405 amplifier back in the 1970s. Very little is new these days, just the sales pitch generated by the marketing departments...

 

[Cereal Killer]

The whole chassis/chrome lid is millied for a solid block of alloy, its c7-10mm in the middle/general depth, there's 40mmx30mm around the perimeter and even bigger section in the corners. Temp on my then 220 pro reached around 42-43c so should be good for the 2x7w class A. Also the base plate is cast alloy and transfers heat from the chrome top. Again a clever design.

 

[davidsrsb]

Maybe 7W dissipation, 2x7W output would mean dealing with about 30W idling, which is a lot when you also have the psu, dsp and class D to factor in.
Smooth shiny boxes don't lose heat well by natural convection, no matter how thick the metal is.

 

[Cereal Killer]

 

[Darth Vader]

Looks like the various Devialet marketing groups haven't got their act together Here is a block diagram about ADH and its a little different than above but which I feel is more accurate:-

You can see that the analogue class A stage is at the heart of the amplifier. I wonder where they get that 'magic wire' from?

Cheers,

DV

 

[Jim Audiomisc]

I get the impression they are skating around saying, "OK, It is current dumping, but using a switching amp to replace QUAD's conventional 'dumpers'." Perhaps (not) adding, "We also run an analysis on your choice of speakers so we can model them and avoid having to rely on feedback to take them into account."

I found the mentions here quite interesting as I've not previously looked into their amps at all. So I've learned something new to me... but not quite sure what!

Maybe they got their 'magic wire' from the same store that PJW was trying to find when he was after 'wire with gain'. 8-]

 

[TheDecameron]

I’m absolutely delighted with the functional integration and performance of my Devialet. It could not be further from the infamous blight of exorbitantly priced flat earth black biscuit tins that once ruled the roost in this country.

 

[davidsrsb]

Nothing wrong if it is a current dumper, the Quad patent is expired. Actually the lack of patents hints that this is an update on old technology

 

[Jim Audiomisc]

Nothing wrong if it is a current dumper, the Quad patent is expired. Actually the lack of patents hints that this is an update on old technology

Must admit I was tempted years ago to claim the 732 design was 'current dumping' on the basis that the drivers were the 'class A amp. and the main output devices 'dumpers'. But I decided it was too cheeky. 8-]

 

[AndrewM]

............You can see that the analogue class A stage is at the heart of the amplifier. I wonder where they get that 'magic wire' from?

Cheers,

DV

It must be that fabled “straight wire with gain” that we’ve all heard of but never actually met

 

[Tim F]

Possibly a nonsense question but what are the key differences between amplifiers other than the obvious class A / class AB etc. implementations (and the power each amp has)? Can these amplifier differences be grouped in a more granular way i.e. are there different types of class A? (particularly interested in this class).

If there are no sub groups, do the differences in sound come down to the quality of components in the amps? (assuming identical power output).

 

[martin clark]

It must be that fabled “straight wire with gain” that we’ve all heard of but never actually met

I suspect a lot of people who inhabit hifi forums, if they did meet such a thing, actually wouldn't like it much.
At least you could expect them to appear in the small ads in droves about 3-6months after teh initial rave reviews, at least.

 

[GT]

The whole chassis/chrome lid is millied for a solid block of alloy, its c7-10mm in the middle/general depth, there's 40mmx30mm around the perimeter and even bigger section in the corners. Temp on my then 220 pro reached around 42-43c so should be good for the 2x7w class A. Also the base plate is cast alloy and transfers heat from the chrome top. Again a clever design.

If you know anything about amp design, Class A, and heat dissipation, then you will know that a plain slab of metal will not dissipate heat very well. You need a large surface area plus lots of airflow which is why heatsinks have large fins and lots of them. Alternatively, you have to consider fan cooling. Hot air rises so having a substantial base won't do a lot to dissipate heat apart from holding the heat inside the amplifier. You need to get the heat quickly away from inside the case where the electronics are, otherwise, the heat will cause many problems.
Take a look at the Tron Antares Headphone amplifier. The whole of the top plate is machined from a 16mm thick alloy billet with raised square fin sections to increase the surface area. This top plate reaches about 50 degrees C with only 2 x 2.6 watts of power into 8ohms and 2 x 0.65watts into 32ohms!!! This is a true Class A amplifier design.

To make a proper class A amplifier is not easy and 99% of manufacturers exaggerate or over-egg their specs to gain sales. Unfortunately, a lot of reviews today just refer to manufacturers specs, instead of actually measuring and working out if their specs are accurate.
Hi-Fi News and Stereophile magazines actually, a good job of measuring equipment and publishing the results.

 

[Cereal Killer]

In the vid above Devialet describe it as class A voltage/gain aided with class D current. FF to 1:00m in and they go all tech.

 

[Darth Vader]

Possibly a nonsense question but what are the key differences between amplifiers other than the obvious class A / class AB etc. implementations (and the power each amp has)? Can these amplifier differences be grouped in a more granular way i.e. are there different types of class A? (particularly interested in this class).

If there are no sub groups, do the differences in sound come down to the quality of components in the amps? (assuming identical power output).

Yes. The types I know are a) single ended b) push-pull and c) cascode. However this is really for the purists. Type a) is considered to be the best and is used in low power designs however when you really want a lot of power say 100W plus the other types can help reduce the size, weight and cost with very little degradation. So if you have the dosh and the space and servants to lug the stuff type a) is the way to go. To give you an idea 100W class A single ended will come in at 100lb plus, as large as a regular floor standing speaker and dissipate around 500W and thats just for a mono channel so you need to double up for stereo. Don't ask the cost as you'll be able to buy one or two new cars for the price!

Cheers,

DV