2. amps-preamps
  3. 162022-139155

When does my class Atoll IN200 A/B integrated switch from class A to class B?

I have an Atoll IN200 integrated amp (earlier version of this: https://www.atoll-electronique.com/en/products/integrated/integrated-in200sig/)

Having read a lot of praise about class A power, I’m wondering how to tell from specs when my integrated likely needs to switch from class A to class B?

The reason I’m curious is that I’m still wondering how my speakers might sound with a pure class A amplifier (such as Pass, etc.) but perhaps the integrated I have is already demonstrating much of that if there is a long enough delivery of class A power from it already? My speakers are 8 ohms, 87 db sensitivity, standmounts.

I apologize if this question is too simple; I hope I’ve posed it clearly.

P.S. This is not about dissatisfaction with my integrated or other gear (I have tubes, too). It's really just part of a longer term attempt to understand how different power sources change the character of a system, particularly the speakers.
128x128hilde45
twoleftears's avatar
twoleftears
5,318 posts
 
https://positive-feedback.com/audio-discourse/leaving-class-a-2019-redux-a-biased-opinion-from-nelson-pass/
Unless the manufacturer specifies the transition point or some magazine has done the measurements, I don't think there's any way of knowing exactly.  Manufacturers tend to boast about amps that run well into A before leaving and going into AB. So if a manufacturer doesn't specify, it's probably very low.
Still, the difference in sound that you might hear between your Atoll and a Pass or a Sugden isn't all attributable to class AB vs class A operation.
hilde45's avatar
hilde45 OP
4,974 posts
 
Thanks, @twoleftears 

I'll try to track down reviews to see if this was measured.
oldhvymec
5,101 posts
 
I know this the higher, the transition point, the hotter the box runs..
Normally until they hit that tipping point they start cooling off. Idling they would run hotter, why the bias is set higher, the tipping point..they cool off until you REALLY push them...they heat up again.. Get yourself a cheap thermal gun, you might be surprised what you can learn from one, and if the left and right are biased the same... Could be load induced, but interesting, none the less.

Regards
hilde45's avatar
hilde45 OP
4,974 posts
 
Thanks, oldhvymec.

I think you all can see the direct interest in this question. Many people on this forum debate different classes of amp, including Class A vs. Class A/B.

If, for a given set of speakers/usage, a Class A/B amp is running nearly all the time in Class A mode, then there would be little reason to investigate pure Class A amps, except for whatever interest their design might offer the music.

As an aside, I know that certain old Adcom amps such as the GFA555 are still prized on the used market; one reason is the famous designer, but another is because this design supposedly ran longer in class A mode before switching to class B.
hilde45's avatar
hilde45 OP
4,974 posts
 
I wrote to Atoll and they responded right away. They said, 

"The IN200 works in Class A up to about 40W under 8 Ohm. The switch to Class AB is quite slow."

Does anyone here have a sense of what that might mean in practical listening terms?
More to discover