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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
rockrider
181 posts
 

Hi @hilde45,


Maybe you’ve already read this interesting article about class A by Nelson Pass:  https://positive-feedback.com/audio-discourse/leaving-class-a-2019-redux-a-biased-opinion-from-nelson-pass/


So, if you know the idle power draw of your Atoll IN200, you could infer somewhat where the class A bias is set. 


(Idle power draw is with the amp fully powered up and ready to play music, NOT “standby” power which might only be enough circuitry to receive a remote power-on command.)


For example, the Luxman L-590AXII is rated at 30 WPC class A, and burns 260 watts at idle. Assuming 40 watts of the 260 is the PreAmp section, that leaves 220 watts idling to drive 60 watts for 2 channels of class A. In this case the power amp idle draw is about 3.7 x the class A power rating. 


Since Atoll does not appear to publish their idle power draw, you could use something like an inexpensive Kill-a-Watt power meter to get you in the ballpark. If it only draws 30 watts at idle then you probably have trivial class A after accounting for the PreAmp. 


I built a little Pass designed Amp Camp Amp, but found it wasn’t up to the sound quality I’m after, and I would not recommend judging any other class A amps based on this small amp’s performance. But it was fun to make, and I’ll probably never sell it.


I find this stuff interesting. Happy holidays!

hilde45's avatar
hilde45 OP
4,974 posts
 
@rockrider Thanks for the suggestions!
The relevant Atoll technical specs I can find are:
Power Wrms/channel/8Ω = 120 W
Power Wrms/channel/4Ω = 200 W
Impulse Power = 200 W
Power supply (VA) = 670
Total of capacitors (µF) = 62 000
Input Impedance (kΩ) = 220
Sensibility (mV) = 100
Rising Time (µs) = 2,5
Signal/Noise Ratio (dBA) = 100 dB
Bandwidth = 5 Hz – 100 kHz
Weight (kg) = 12

If those aren't enough to answer the question (I presume they are not) maybe I can do some measurements.
rockrider
181 posts
 
Correct - not enough info there. 
I should mention, we are talking about “traditional” class A with respect to the idle power. If Atoll is using some variable bias scheme (like Krell’s iBias “sliding bias”), then all bets are off. But that’s not traditional class A like I think you are asking about. 
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