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Pass Amps Class A operation

I just started using a Pass Labs X150.0 power amp. Love it so far. I know that it operates in Class A mode up to a certain point - I think 10 or 15 watts. How does that translate into approximate volume level? Is 15 watts coming out of this amp (into Sonus Faber Grand Piano speakers) generally enough to drown out all conversation in a 20 x 15 room? Or is 15 watts a volume level that is easily and typically surpassed, except when listening at midnight in an apartment with thin walls. In other words, I am trying to gauge how much of what I am listening to is Class A mode and to get a general sense of where the Class A/B transition point is. Is there a way to tell? The meter on the amp never seems to get more than approx 25% towards pegged (or move much at all for that matter). I also have read that this amp actually puts out much more than 150 watts (200-250?), even though 150 is the published rating. Is the Class A crossover similiarly conservatively rated, or is that a more precise number?
gipp
studio68
17 posts
 
From my recollection, I believe once the meter needle starts to wiggle, that means the amp is not in Class A mode anymore and is in A/B mode. To be in Class A mode, the meter needle would be still. Hope that helps.
stanwal's avatar
stanwal
3,147 posts
 
The sensitivity rating of the speaker is it's output with one watt input. To find out how loud 15 watts would be add 3 db for every doubling of output. IE, 2 watts would be 3 db higher. These are generally measured at one meter so room size and shape will determine your perceived level. 15 watts is usually quite loud. Under the conditions you describe I would think that virtually all of your listening would be in class A.
marakanetz's avatar
marakanetz
5,473 posts
 
If you filter out the bass freequencies, than 10...15 watts will be pretty loud.
Otherwise it would mostly work in class B.
Typically the most of power goes towards bass freequencies and crossover point so even playing 1-st 2nd octave piano notes at moderate volume level(similar to natural loudness of the instrument) may cause switching to class B.
dne
141 posts
 
As an owner of a Pass 150.5, it transitions from Class A to A/B at 15 watts. It's just as Studio 68 said above -- the needle doesn't move in Class A, and moves up from rest when the amp goes to A/B.

So, the answer to your question, since you already own the 150.5 and the SF speakers, is simply to try play it and watch the meter. Question answered.

BTW, I'm always surprised at how much volume those 15 Class A watts can produce, even on my Magnepan 3.6's (85db sensitivity). For most material, it's reasonably loud.
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