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  #21  
Old 02-25-2022, 10:15 AM
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From an engineering standpoint class AB is not that far off from class A (depicted on a load-line showing percent conduction at various bias points). However the alure of class A is undeniable. Esoteric's F03 (30w class A) is wonderful and fits in this discussion perfectly. My personal choice will always be an AB biased amp. I prefer my equipment left on 24/7 and class A amps simply run too hot.
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  #22  
Old 02-25-2022, 10:42 AM
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Quote:
Originally Posted by tdelahanty View Post
From an engineering standpoint class AB is not that far off from class A (depicted on a load-line showing percent conduction at various bias points). However the alure of class A is undeniable. Esoteric's F03 (30w class A) is wonderful and fits in this discussion perfectly. My personal choice will always be an AB biased amp. I prefer my equipment left on 24/7 and class A amps simply run too hot.
You neglect to mention the small matter of crossover distortion !
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  #23  
Old 02-25-2022, 02:31 PM
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Originally Posted by Iansr View Post
You neglect to mention the small matter of crossover distortion !
Crossover distortion in today's amplifiers is over blown!!!!! Modern transistors are much more linear during small signal conditions (the period when the device first begins to conduct)
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  #24  
Old 02-25-2022, 03:19 PM
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Au contraire. Crossover distortion is still a 'real' problem when transistors in the output stage are not well matched and one of the cost drivers of our high-end solid-state gear. The time & expense of finding good matched sets is non-trivial. Especially when one has a dozen or devices for each channel. Sorting, testing and matching is a expensive.
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  #25  
Old 02-25-2022, 03:24 PM
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Quote:
Originally Posted by audio bill View Post
I only pointed out that operation is only specified as being in 'Class A' for the rated power into 8 ohms and you can see that in their specs as the ratings into lower impedances are not designated as 'Class A'. The class of operation goes into AB into impedances lower than 8 ohms at the rated power levels.
Sorry again, but no again.
The class of operation does not go into AB into impedances lower than 8 ohms at the rated power levels.
Rated power levels are all class A.


Download the 'technical information from their homepage
https://www.accuphase.com/technical_...nformation.pdf
and have a closer look at the power specs:

The rated class A output power (marked in red) is 30W@8Ω / 60W@4Ω / 120W@2Ω and 150W@1Ω.
The maximum output power (marked in orange, class AB) before clipping is 75W@8Ω / 125W@4Ω /190W@2Ω / 220W@1Ω.

This means:
@8Ω it's up to 30W in class A and from there further up to 75W in class AB
@4Ω it's up to 60W in class A and from there further up to 125W in class AB
@2Ω it's up to 120W in class A and from there further up to 190W in class AB
@1Ω it's up to 150W in class A and from there further up to 220W in class AB

Martin
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  #26  
Old 02-25-2022, 04:40 PM
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Transistors are not BETA (gain) matched to eliminate cross-over notch distortion. They are matched to ensure equal conduction of the pos/neg signals and that no one transistor will conduct more or less than any other in the output stage. Class A and AB are biased "on" enough to eliminate notch issues.
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  #27  
Old 02-25-2022, 04:52 PM
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Quote:
Originally Posted by tdelahanty View Post
Crossover distortion in today's amplifiers is over blown!!!!! Modern transistors are much more linear during small signal conditions (the period when the device first begins to conduct)
It is extremely misleading and frankly irresponsible to suggest that cross over distortion is not an issue given that there may be people with little or no technical knowledge reading this. Try posting such an assertion on DIYA and see how long you last.

Hugh Dean is a hugely respected amplifier designer. He openly admits that he has spent the last 25 years or more trying to design a class AB amp that sounds as good as a well designed class A amp. (He dislikes the inefficiency of class A). Perhaps you should contact him and tell him where he is going wrong.
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  #28  
Old 02-25-2022, 08:08 PM
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Quote:
Originally Posted by meltemi View Post
Sorry again, but no again.
The class of operation does not go into AB into impedances lower than 8 ohms at the rated power levels.
Rated power levels are all class A.


Download the 'technical information from their homepage
https://www.accuphase.com/technical_...nformation.pdf
and have a closer look at the power specs:

The rated class A output power (marked in red) is 30W@8Ω / 60W@4Ω / 120W@2Ω and 150W@1Ω.
The maximum output power (marked in orange, class AB) before clipping is 75W@8Ω / 125W@4Ω /190W@2Ω / 220W@1Ω.

This means:
@8Ω it's up to 30W in class A and from there further up to 75W in class AB
@4Ω it's up to 60W in class A and from there further up to 125W in class AB
@2Ω it's up to 120W in class A and from there further up to 190W in class AB
@1Ω it's up to 150W in class A and from there further up to 220W in class AB

Martin
I'm afraid we're interpreting the specs differently but I have to respectfully disagree with your assessment. In the document you linked to as well as the specs I provided they consistently specify the rated output power as being in Class A only in its 8 ohm rating. I don't see anything stated in either document or even any implication that it maintains pure Class A operation into the lower impedances. The higher power output shown in orange is additional headroom available beyond the rated power before clipping, but I don't see anything stated there relating it to the Class A or AB power bias points.

This is common in what are referred to as Pure Class A bias (fixed bias) amps since the output devices and heat sinks cannot dissipate the amp's full rated power into lower impedances. I don't intend to get into a long winded dispute on the topic, so I'll respectfully bow out of the discussion at this point. For the record I love the sound of Accuphase gear having owned one of their Class A amps in the past and have nothing but respect for their design quality and sonic performance.

Last edited by audio bill; 02-25-2022 at 08:54 PM.
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  #29  
Old 02-25-2022, 10:10 PM
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Quote:
Originally Posted by Iansr View Post
It is extremely misleading and frankly irresponsible to suggest that cross over distortion is not an issue given that there may be people with little or no technical knowledge reading this. Try posting such an assertion on DIYA and see how long you last.

Hugh Dean is a hugely respected amplifier designer. He openly admits that he has spent the last 25 years or more trying to design a class AB amp that sounds as good as a well designed class A amp. (He dislikes the inefficiency of class A). Perhaps you should contact him and tell him where he is going wrong.
I assume you are one of the people reading this thread with little or no technical knowledge.
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  #30  
Old 02-25-2022, 10:21 PM
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I don't quite understand these technical descriptions between the Class A and AB versions of Accuphase amplifiers.

What I have been playing with are the E380 (directly to a pair of Amati Traditions) and using the E380 as a preamp to the A48 (again to the Amatis). Source is a dCS Bartok. Wireworld Silver 7 cabling.

I definitely prefer the E380 driving the Amatis. There's just better control to me especially of the Amati's bass drivers.

Also, the A48s benefit greatly from using the E380 as a preamp. I had the dCS directly into the A48 and it sounded drier and more lifeless. The E380 (as a preamp to the A48) just gave it such a breath of energy and realism
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