[Adarsh]

Is there anyway to tell if an amp is class A?

[Adarsh]

Can you tell by the heat?

[Rocket]

Hi,

Yes you can fry an egg on it   .

Regards

Rod

[Florian]

What does it mean anyways. I know my Jolida Pre and my Krell KSA are class A. Is it like a "QA" thing. Sorta like saying "its grade A meat" ?!?!?!

[Taz13]

A linear electronic circuit such as a gain stage of an amplifier is said to be in Class A if the device is operating within its nominally linear region at all times.

This contrasts with class B where (typically a pair of devices operating in push pull each) only operate in the linear region some of the time.

The primary advantage of class A is that it does not suffer from transient distortion that occurs in class B devices when passing out of the linear region, and for this reason class A circuits are often preferred for small signal circuits, it being normally the case that linearity (excluding noise) increases as the signal amplitude is decreased. The main disadvantage with class A is that it is not very efficient, a substantial amount of the power drawn by the circuit being wasted as heat (which also increases the size of the designers problem of getting rid of this heat in some cases - high power class A circuits are as much engineering challenges as circuit design problems)

As a comparison, circuits operating in class B, best performance occurs at high power levels (typically just below clipping), but since the distortion products due to leaving the linear region are constant, these become relatively larger as the signal is made smaller, such that at very small signal levels the distortion levels are very high.

For these reasons most small signal circuits requiring accuracy tend to use class A, whereas high power circuits almost always use class B

Class A circuits are often single ended but a classic application for a pair of class A devices is differential long tail pair, which is exceptionally linear, and forms the basis of many more complex circuits, including many audio amplifiers and almost all op-amps

Does this help?

[Adarsh]

So how do you tell? Can you verify by observation?

-A

[Florian]

That explains a lot. So its true that the High Powered Class A amps are basically the non-compromise solutions. They are highly inefficient but produce the best sound ?  

I dont think it says on the units what class it is. I read in my manuals that it is class A. And my Krell modell number is "KSA"  

[Taz13]

I can't say best sound, only your ears can. But it will produce the cleanest sound as there is no switching noise. Also a class A output device is always conducting current, and in class AB the output device switches off for 1/2 the cycle, hence a push pull output. One way that might give a clue if you have a class A is low audio power out with high AC power in. Most pre amps I have worked on are class A. Low output very clean. Class A normally means quality or best.

[Florian]

Great to know. My Jolida and Krell are both Class A. The Krell puts out 150@8ohm and 1200@1ohm and can drive below 1ohm loads    

[guest1632]

Great to know. My Jolida and Krell are both Class A. The Krell puts out 150@8ohm and 1200@1ohm and can drive below 1ohm loads    :D

Hi, Well that Krell might be class A probably to a certain point then switches to Class A/b or Class B. To have a fully Class A power amp, would mean a rather expensive power supply, let alone the current draw from your wall socket.

Ray

[Florian]

It says its pure class A. This was the pure class A series from Krell back in the Apogee days. The PSU etc are huge......He weighs 100lbs  

I can post a picture of his insides, its really cool !!

[Adarsh]

If you can also post one of the exterior.

-A

[ted_b]

There's a poor sideview of my Krell KSA 100 in my gallery (sitting on floor in front of my room with a couple of VPI bricks on it).  It's a 17 yr old space heater, but it drives the RM/X's beautifully. Eventually it will be replaced, but I keep hearing great things from it (single amp driving full-range) so I keep putting off that purchase.  Class A and loving it.

Ted

[Florian]

Ok here we go      Good?

[dado5]

First this only applies to the output devices. Small signal portions of amplifiers are nearly universally run in class A.

Secondly, anything single ended has to be in class A operation. This is the only real dead give away. This is almost exclusively the domain of the SET tube amp.  Nelson Pass is the only guy I know to have successfully produced a line of single ended solid state gear.

Aside from that, heat is probably the best external guage of operating class, though it is far from perfect.

If an amp operates in  class A, it will produce a lot of heat. In fact, maximum heat dissipation will occur when  no signal is present - yep it will be hotter idiling than when playin' music. It's pretty obvious with tube gear. AB class PP stuff is hot to the touch for the most part, but class A is extremely hot - you can feel the heat radiating for a good distance away. Touch a halogen light bulb and you will get an idea of class A tube heat.
Solid state is more difficult to guage, but if it has big fins and they get hot quick when the amp is idle, it is likely operating in true class A.

Of course lots of manufactures technically overstate the case for class A in their equipment. This is most common among solid state and tube OTL makers. The equipment actually operates in a high AB condition, with the idle current still  lower than the signal current. In these cases all but the highest peaks of the music signal are passed by both PP output devices without clipping, hence they are operating in a class A like condition most of the time without technically being biased for class A operation.  Again if it runs cooler in idle than when  it plays, it aint true class A.

Hope this helps.
Rob

[Florian]

Sure does, i now know its a true class A. The little bastard gets really hot.  

[Adarsh]

How many watts does it produce? It looks like a Public Adress system.
How much does it cost?

-A

[Florian]

It produces as follows ///    say what do you mean by public adress?

150@8ohm   (220 actually)
300@4ohm
600@2ohm
1200@1ohm
and goes below 1ohm according to Krell

[lcrim]

My Decware Select SET amp runs completely in Class A but only produces 1.8 Watts so the amount of power has nothing to do with what Class a component runs in.  As stated earlier, this has to do w/ the design topology.
Just how good a component sounds is a very subjective thing and has nothing to do with what class it runs in.

[Florian]

I didnt buy my Krell cause of the Class A thing. There are several reasons why i bought it.

1. I always wanted a Krell
2. I wanted the option to buy any speaker i want whithout having to buy a new AMP
3. It has sooo many deatils, and its cold and brutal (great for my music)