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Class A?  Really?
Class A?  Really?
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Old 17th September 2021, 02:59 PM   #111
mocenigo is offline mocenigo  Germany
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Quote:
Originally Posted by andyr View Post
OK, Jan ... perhaps you can explain how FFT techniques will explain what is going on when 2 different amps produce the following results - using the same source and into the same pair of spkrs. The amps are:

1. a Purify 452 (I think the model is) stereo amp.
2. A pair of Audio Research 250SE tube monoblocs.

#2 produced a deep soundstage, from the plane of the spkrs to waaay back.
#1 had a flat soundstage.

This difference was easy to hear ... I'm curious to know what measurements would explain the difference we heard.

Andy
Maybe a #2 had some small amount of negative H2?
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Old 17th September 2021, 03:05 PM   #112
mocenigo is offline mocenigo  Germany
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Quote:
Originally Posted by andyr View Post
Yes, it is not your average Class A. It sounds absolutely wonderful, though! I built 2 of the 4R version, as they needed to power the 3ohm mids and 2 ohm ribbons of my active Maggies.

Here's the link: Alpha Nirvana 39w 8ohm Class A Amp - diyAudio
AAAAAAH! Ok, that one. Well, that's an intentionally voiced amplifier. Never heard of it but many people like it a lot. It must be good, I would say.

It is single ended because it generated only one hot signal wrt ground.
It can be called a push pull because it uses two Mosfets (one PNP, one NPN) to simultaneously drive the signal from "both sides" and
It is in Class A because the two mosfets are always conducting.

At the same time, it is a bit weird because if I understood correctly the two mosfets do not work in a completely symmetric way in order to not completely cancel even order harmonics. And it still has a subjectively pleasant sequence of decreasing harmonics.

Never heard it, but I am quite sure one can prefer it and it can also get a perception of deeper soundstage and higher dynamics (the latter because of the distortion as well).

Nothing that could not be emulated with some digital processing and more neutral components, of course, whereas to "fix"it in order to make the result more neutral would be more difficult. However, at the end we choose what we like and often we choose what to choose to like, which is absolutely fine.
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Old 19th September 2021, 04:42 AM   #113
wirewiggler is offline wirewiggler  United States
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The reality is you can build a pretty simple class A amp and it will sound pretty good. To achieve the same perceived quality of sound in AB is a considerably more complex design. Then you have to add we come with one of the most sophisticated DSP processors (our brain), when your brain knows what it should sound like it will attempt to adjust. I can remember ( this will date me) getting in my old truck with a factory AM radio and turn it on and it will sound horrible for half a second then the brain kicks in. I think one of the most difficult part for designers and reviewers is to turn off their internal DSP.

Bill
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Old 19th September 2021, 06:56 AM   #114
jan.didden is offline jan.didden  Europe
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Peter Walker from QUAD fame used to say that he never listened to prototypes, only to the final product. That didn't stop him from turning out first-rate products.

Jan
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Old 20th September 2021, 04:41 PM   #115
wirewiggler is offline wirewiggler  United States
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It is kinda of funny 40 years ago I just thought I had bad hearing then I went to work at a Hifi store and realized I just had bad equipment. I have been pursuing better equipment since.

Bill
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