Accuphase" A" line amps, are they pure Class A and nothing else?

R

robhifi

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"Stereo Sound" is a reputable magazine in Japan.
I haven't read every single issue but for few times,I read reviewers （well known figure in the Japanese audio industry) mentioning something like this about A45 and A65:
" Dont' worry about A45/A65's speaker driving capability, it is class A before reaching 45w/60w and there is class AB picking up afterwards....."

That bothered me a little.

It's worth mentioning the magazine uses Accuphase gear (A200,A65.E460 etc) as their reference system so they should know what they are talking about.

I am not saying I have a problem with class AB. It's jus tthat my previous understanding of Accuphase "pure Class A" amp isn't really that pure.

One more thing, I own only A35 which outputs 30wx2 in Class A. However, when running in bridged mode, it turns itself into a 120w mono amp.
So is that 120w pure class A too?
 
Rob, at some point based on increasing load and demand, all class A amps CAN leave Class A and go into AB. That being said, most people never get this far if they match their amp to their speakers properly. If your speakers are efficient or if you don't drive the hell out of the amp by pushing it too hard on lesser efficient speakers, than you should always stay in class A.

I've heard the A65 pushed too hard and when it leaves class A, you'll know. It sounds downright nasty (because distortion goes way up).

If you're looking at A65 (now replaced by the A70 I believe), make sure your speakers are at least 92db efficient, preferably higher.
 
I believe that Accuphase Class A power amps do indeed maintain their Class A bias up to their stated ratings, and then may provide some additional headroom in Class A/B. Since you stated that Stereo Sound's "quote" above was "something like this", I suspect that there may be a slight difference in what you stated and their intended meaning, possibly from a translation issue. As far as maintaining Class A bias when operating in bridged mode you raise a valid point. Since true Class A biased amps run at their full rated power at all times, any unused power (which is not delivered to and used by the speaker load) must be dissipated as heat in the amp's heat sinks. That's why they run their hottest when idling and not delivering power to the speakers. When powering speakers only the unused portion of their rated power has to be dissipated in the heat sinks since the speakers are dissipating the balance. The heat sink's dissipation capacity is usually maxed out in standard (non-bridged) operation, so that when an amp is bridged it cannot maintain pure Class A bias under the additional current demands that bridged operation presents. With your A35 for example, it runs at 30 wpc or 60 watts total in Class A bias. It cannot handle the heat dissipation of 120 watts when bridged, so it will resort to Class A/B bias when bridged at its higher rated power levels. There are likely some exceptions to this, but most 'Class A' bias amps operate this way when bridged.
 
I own an A-70 and with Focal Scala speakers, 20 watts on the output meters is ear splitting loud. with reasonably efficient speakers you never need more than the rated 60 watts, even with rock music.
 
Thanks guys for all the useful info and they are highly appreciated.

I still think the term "pure class A“ is a little misleading.

Common sense was telling me that A35 wouldn't do 120w in class A when bridged, not with that headsink in that size.
A full class A mono amp would requrie heatsinks the size of a refrigerator.

For now, my small room(3x4.5 meters) is the biggest constraint. I could only stick to 2 way monitors (I have 6 pairs of them and the 7th pair Raidho x1 is on the way).

Full range floorstanders just couldn't accommodate. Believe me I tried, even "big monitors" like ProAc D2 produced too much bass in my room(with 4 bass tubes installed).Not mentioning the complaints from the neigbors. To my limited knowledge about speakers, almost no monitors has sensitivity above 90db.

Anyway, I guess my next upgrade would be either P6100 or A70. The 'pure class A" thing shouldn't bother me anymore.

Thanks again guys.:rolleyes:
 
dfwmediagroup said:
I own an A-70 and with Focal Scala speakers, 20 watts on the output meters is ear splitting loud. with reasonably efficient speakers you never need more than the rated 60 watts, even with rock music.
Click to expand...

df, how hot is your A70?
I had always heared that class a amp is extremly hot(fry egg)but that's not the case with my A35. Even in summer, it is just "very warm".
Nowhere as hot to touch as say Krell 400xi(200w x2)intergrated I owned many years ago.

And any plan to upgrade to 2820 soon?:rolleyes:
 
My A-70 is warm, but never hot, even when turned on for hours at a time. The Krell, BAT and Pass I have had run much hotter. And FYI, I just upgraded my preamp from 2420 to 2820. Quite a difference.
 
dfwmediagroup said:
My A-70 is warm, but never hot, even when turned on for hours at a time. The Krell, BAT and Pass I have had run much hotter. And FYI, I just upgraded my preamp from 2420 to 2820. Quite a difference.
Click to expand...
Df, great move and the right move:P.
How different is 2820 to 2420?
would u be so kind to describe briefly?
 
A more explicit presentation with more detail, more dynamics and better extension at both ends of the frequency spectrum in the bass and in the treble. Also a quieter background.
 
dfwmediagroup said:
A more explicit presentation with more detail, more dynamics and better extension at both ends of the frequency spectrum in the bass and in the treble. Also a quieter background.
Click to expand...

Thanks DF,very tempting comments.
I guess your SCALA plays a major role in revealing of all the positive things mentioned.
 
I've had both p-6100 and A-70 in here. The A-70 is superior in all respects and sounds more powerful than the class AB amp.
 
agree as well, id take the class a accuphase if funds permit over the a/b counterpart... it may look in paper small wattage but its very conservatively rated... its quite powerful really.
 
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