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

Showing 12 responses by hilde45

So, guys, all I can tell you is this is what they told me. It has dual toroids but...I'm just a lowly humanities guy. If they're lying directly to a customer, that would be pretty wild. Of course, their native language is not English, but they're an international company. Whatever. Another mystery.
Thanks, @twoleftears 

I'll try to track down reviews to see if this was measured.
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?
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.
I wrote to Atoll and conveyed the skepticism posted here about the Class A operation of the Atoll. They replied:

From Atoll engineers:
"Hello, Thank for for this information.
This is one of the most current mistakes people make about our amplifiers; they compare the size of our heat-sink to a single one; this is nonsense regarding to thermal dissipation because when you use a single, big heat-sink you have to put in isolation components that increase (a lot) the thermal resistor. For that reason, and on that point they are correct -- in order to have the same dissipation you would require an almost 10 times bigger heat sink for each channel; but with our trick, the transistors are transferring about 100% of their heat to the heat-sink with no waste of energy. You'll find attached a measurement that shows the distortion when power is rising; as you can see (in the picture), the distortion is under 0,002% up to 50W on both channel. Best regards. ATOLL Team"

I don't think I can post pictures here, but anyone who'd like to see it can P.M. me.
Thank you George and others. You have told me what I wanted to hear, namely the truth with explanations. I did not buy this amplifier with the expectation that it would be class a for very many watts.

I think this inquiry has taught me something also about what this company is willing to say even when they know that it is being repeated into a forum.

If I have more dialogue with them I may just share it with you because it's kind of amazing how long they are willing to stick with this line of bs.
Quick follow up. I discovered this comment about their more advanced amp and I sent it to Atoll:

What I found said,

“The high bias allows the IN400SE to operate in a Class A for the first ten watts before going into Class AB operation."
http://www.theabsolutesound.com/articles/atoll-electronique-in400se-integrated-amplifier/

And I asked Atoll if they were claiming the my IN200SE operates to 40w in class A while a later and more expensive model only operates in Class A for the first 10 watts? If that is true, why did you not employ this technology in the later amp?""

They replied: "The IN400se use almost the same technology as the IN200se so both work in class A up to the third of the maximum power."

So, they're in contradiction. Is it Class A up to 10w or to 40w? They seem to say both but insist (to me) that it's 40w in Class A. Despite the lack of heat, fins, etc.

They're just jerking me around at this point, right?
It seems proved as BS. What I'm amazed at is that I confronted them via email with the evidence it couldn't be true and they just repeated the BS. I may give them one more chance to come clean but nothing really hangs on it -- I'm just a berserker-against-BS.
@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.
George, I’ve quoted them verbatim. They claimed it twice. 
I like their product. That’s not in question.