By the way, this is what I was talking about regarding the lack of a zero crossing spike in a properly adjusted AB amplifier (stolen out of an old review of @Kal Rubinson of a very non-exotic Adcom home theater amp).
+1The guy I was visiting last night is a fan of Wilson speakers, which are infamous for that. In my mind, that's a pathologically bad design, but if one is committed to them, yes, a more elaborate power amp is needed than for driving what I would consider better engineered speakers. The amps I use wouldn't hack it.
With speakers having a non-pathological impedance curve, Aczel's maxim remains true.
Maybe it is because in the Swedish LTS series amplifier testing only one amplifier has ever been straight wire transparent in both sighted and blind listening and that amplifier is a Bryston SST.
http://mjaudiolab.pl/images/stories/Bryston/swedish14bsstreview.pdf
y the way, this is what I was talking about regarding the lack of a zero crossing spike in a properly adjusted AB amplifier (stolen out of an old review of @Kal Rubinson of a very non-exotic Adcom home theater amp).
I'm not questioning the excellence of Bryston's SST. Rather I'm trying to reconcile why an owner of such an amp would advance/repeat the facile assertion about amps of certain equivalences sounding the same.
If this is Daverz view (and I'm not saying it is because I get the sense he's just trying to be provocative), perhaps he could provide a contrasting series of views to those presented by John Siau on how micro acoustics (my expression, offered as a way of framing many of the issues carefully articulated by Mr. Siau) can be captured though curiosity-discovery when the characteristics fall outside the common metrics captured and presented by the industry?
I think Daverz understands this unless his choice of amp was purely by chance. Either way, he's a fortunate person...
Here's a Pioneer brochure from July 1985...
Take another look. The transients occurs about half way between the zero crossing and the peaks of the sine wave which is 2.83 Vrms which is 8 Vpp. The transients are occurring at about +/- 2 V.@John_Siau Not sure if my question got lost in the morass. Am I looking at this incorrectly?
I would add one more: The phase response needs to be linear. You can have a flat frequency response without having a linear phase response and the non-linear phase response will change the way transients sound. A non-linear phase response will have no impact on a continuous set of tones, but it will change the apparent frequency response of transients.Found the full quote:
As I have said, and written, innumerable times, any two amplifiers with high input impedance, low output impedance, flat frequency response, and sufficiently low distortion and noise will sound exactly the same at matched levels if not clipped.
http://www.biline.ca/audio_critic/audio_critic_web2.htm#ba
If "sufficiently low distortion" means as low as the ABH2, then in practical terms all amps will sound different.
Take another look. The transients occurs about half way between the zero crossing and the peaks of the sine wave which is 2.83 Vrms which is 8 Vpp. The transients are occurring at about +/- 2 V.
Adjusting the bias could reduce these transients at a given operating temperature, but like most class-AB amplifiers, the bias drifts somewhat with temperature.
Thanks for pointing this out. I will add that note to the feed forward application note. Not trying to be deceptive. Our goal is to present accurate and useful information.OK, there are two articles, the first watt mentions the 60db gain, the feedforward article does not.
https://benchmarkmedia.com/blogs/application_notes/feed-forward-error-correction
The distortion differences are amplified. It's not like they produce 10% or more distortion. It's not easy to adjust out. Or it's not able to be adjusted out completely. Most rely on better designed gain stage and feedback techniques to obtain higher ol gain at high frequency to reduce this. Unless it's class A it's always there at the class b/class ab output stage.Thanks for the response, John. To my eyes, the spikes look pretty close to zero crossing, which would be consistent with your claims about crossover distortion:
View attachment 27010
But as you say, it's easy to adjust out, which is the case for the engineered AB amps I have on hand and have tested. This sort of graph is indeed traditional, but I think it's not exactly representative. Even with thermal drift (which for bipolars and most MOSFETs at the current ranges they're run will take them to HIGHER idle current), an engineered AB amp that isn't misadjusted doesn't show that phenomenon.
Thanks for pointing this out. I will add that note to the feed forward application note. Not trying to be deceptive. Our goal is to present accurate and useful information.
TIt's not easy to adjust out. Or it's not able to be adjusted out completely.
Perhaps a bit of reading of Self and Cordell's books, along with some bench time with power amps and trimmer adjustments, might convince you that this assertion is entirely incorrect.
The theory is good, but a lot of things have to be done correctly. The reality is that most class-AB amplifiers don't live up to what is theoretically possible, nor do they stay perfectly trimmed over temperature, varying loads, and time. This is why it is so important to run low-power THD measurements, before and after heating up the amplifier. It is also a good idea to measure an amplifier that has been in service for a number of years.Perhaps a bit of reading of Self and Cordell's books, along with some bench time with power amps and trimmer adjustments, might convince you that this assertion is entirely incorrect.
The theory is good, but a lot of things have to be done correctly.
As a layman, I am trying to understand this. Every crossover distortion graph for classic feedback Class A/B amps I have seen show crossover distortion in their notched out charts.
Staying contemporary, here are some of the Constellation Performance Centaur II 500 (500 WPC, $55,000) charts from Stereophile: