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In Reply to: RE: Its not important! posted by Ralph on March 30, 2022 at 10:52:13
This approach seems like the best of both worlds. The voltage is Class A, while the current is sourced via Class D. The measurements achieved with this approach are outstanding. It looks like a variation of the current dumping approach.
The DAC being integrated into the ADH amp also helps. No interconnects required. I'm surprised no one else has tried to emulate this topology.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
Follow Ups:
I took a look at the website where they push this idea.
There's a lot of misinformation. I'm guessing its written by the marketing department, by someone not having a grasp of the actual engineering.
The most obvious example is stating that a class D amp is digital and conflating the two. Class D amps are analog and employ switching. They are not digital; if there is a digital amplifier its not class D. Just so we're clear on that.
Its an interesting idea but one question coming to mind right away is since the class D is providing the current, it therefore has to be providing the voltage as well, so the class A portion would be doing nothing! So I have to assume that the explanation is simply incorrect.
I think it's more involved than that. I get the fact that Class D is analog, but when the engineers demonstrated the amp, they disconnected the Class D section, and just use the Class A portion. That only outputs a few watts. The claim is that the Class D provides the current, while the Class A supplies the voltage. It does seem like the Class A does switch the current source.No other amp I'm aware of uses this approach. I can report that it sounds outstanding, and seems to have lots of power.
I'm not sure how it actually works, but it sure sounds better than most any setup I've come across. I agree the write up is likely written by marketing, but I think the approach is unique, to be sure.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
Edits: 03/31/22
There are two amps: a high power but lower accuracy amp and a low power but very hi accuracy amp. The low power amp is driven with a correction signal and it's output is added to the output of the high power amp such that the combined output is as precise as that of the low power amp alone. Or something like that. I've heard it described as a form of feed-forward.
Edits: 03/31/22
Peter Walker must have been born on another planet. I have Quad 57's and a current dumping amp for the quads as well as a few different amps.I remember something like the low power amp is class A driving 2 class C amps, one + the other - , and the waveform put together to then drive the speaker. That's a lousy explanation and I forget how it's done exactly but it sounds quite good. If I also remember correctly, he also invented tertiary windings on output transformers that was later used by McIntosh but received no credit for that.
I once mailed Quad across the pond for help restoring my Uncle's 1957 57's and he personally mailed me guidance and original picture manual of the Quads and how to update them. Back then at 21 Y.O. I didn't recognize the significance of that, what can I say.
edit - I was wrong, it's 2 class B sections not class C
Edits: 04/03/22
Best sound I ever got out of my partially refurbed 57s was with a passive attenuator driving a pair of completely refurbed Quad II tube amps. Never seriously tried them with anything solid state.
NT
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
over the last 40 years of playing music thru them with different amps, they can be extremely revealing. Back then I tried a Phase Linear 400 through them and that was bad. The usual import receiver with loads of feedback was bad. I don't know anybody local with Quad tube amps, my Uncle had a Dynaco Stereo 70 and I have a few different including Mark III's.
Quads have euphonic qualities, at least the 57's. They also throw a wide spacious soundstage beyond the left and right and have a good sense of depth. You can't tell where the mid/tweeter panel is, even with my plain speaker cloth and metal screen long gone. Revealing of sources, yes, so much so that deficiencies in recordings are plainly evident. My quest is over except for music where the money should go.
and not an actual class of operation.
Here is the power formula (which is an extraction of Ohm's Law):
1 Watt= 1 Volt times 1 Amp
From this you can see that if you have a voltage, you also have an amperage. The two cannot be separated, else you cause a new branch of physics!
So if you are driving an 8 Ohm speaker with 10 watts (solving for current first):
10 = 8 times the current squared.
Thus the current is about 1.12 Amps. That means the voltage is about 8.93 Volts. Quite literally you can't have one without the other. I don't know what those 'engineers' did but they didn't switch back and forth between just current and just voltage.
Again, I'm not contesting how the amp sounds nor that it works. I am contesting the explanations I've seen, which fly in the face of basic electrical laws.
Understand your point. They are not very clear on how it actually works.
I think Steve O is onto something with the current dumping/feed forward concept. I had read that one of the Devialet engineers at a demonstration initially played a track with only the Class A amp, then connected the Class D stage.
However it actually works, can't argue with the results. Would have thought by now some other manufacturers would have come up with a similar approach. Maybe it's because it's trademarked?
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
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