Rotel amp classification?

[doodleboytoy]

Just wondering how are Rotel amps classified? Class A? A/B? B? :?:

[greggz]

I know the 1075, 1090, and 1095 are Class A/B. I'm not sure about the rest.




Gregg

[Aeromos]

Can someone please clarify for me the differences that specifies an amp to fall in each class? Thanks!!




Aeromos
Enjoy life, it's too short to waste!!
My Collection

[Danbry39]

From audiofaq.

11.18 What is Amplifier Class A? What is Class B? What is Class AB?
What is Class C? What is Class D?

All of these terms refer to the operating characteristics
of the output stages of amplifiers.

Briefly, Class A amps sound the best, cost the most, and are the
least practical. They waste power and return very clean signals.
Class AB amps dominate the market and rival the best Class A
amps in sound quality. They use less power than Class A,
and can be cheaper, smaller, cooler, and lighter. Class D amps
are only used for special applications like bass-guitar amps and
subwoofer amps. They are even smaller than Class AB amps and
more efficient, yet are often limited to under 10kHz (less than
full-range audio). Class B & Class C amps aren't used in audio.

In the following discussion, we will assume transistor output
stages, with one transistor per function. In some amplifiers,
the output devices are tubes. Most amps use more than one
transistor or tube per function in the output stage to increase
the power.

Class A refers to an output stage with bias current greater than
the maximum output current, so that all output transistors are
always conducting current. The biggest advantage of Class A
is that it is most linear, ie: has the lowest distortion.

The biggest disadvantage of Class A is that it is inefficient,
ie: it takes a very large Class A amplifier to deliver 50 watts,
and that amplifier uses lots of electricity and gets very hot.

Some high-end amplifiers are Class A, but true Class A only
accounts for perhaps 10% of the small high-end market and none
of the middle or lower-end market.

Class B amps have output stages which have zero idle bias
current. Typically, a Class B audio amplifier has zero bias
current in a very small part of the power cycle, to avoid
nonlinearities. Class B amplifiers have a significant advantage
over Class A in efficiency because they use almost no
electricity with small signals.

Class B amplifiers have a major disadvantage: very audible
distortion with small signals. This distortion can be so bad
that it is objectionable even with large signals. This
distortion is called crossover distortion, because it occurs at
the point when the output stage crosses between sourcing and
sinking current. There are almost no Class B amplifiers on the
market today.

Class C amplifiers are similar to Class B in that the output
stage has zero idle bias current. However, Class C amplifiers
have a region of zero idle current which is more than 50% of
the total supply voltage. The disadvantages of Class B
amplifiers are even more evident in Class C amplifiers, so
Class C is likewise not practical for audio amps.

Class A amplifiers often consist of a driven transistor
connected from output to positive power supply and a constant
current transistor connected from output to negative power
supply. The signal to the driven transistor modulates the
output voltage and the output current. With no input signal,
the constant bias current flows directly from the positive
supply to the negative supply, resulting in no output current,
yet lots of power consumed. More sophisticated Class A amps
have both transistors driven (in a push-pull fashion).

Class B amplifiers consist of a driven transistor connected
from output to positive power supply and another driven
transistor connected from output to negative power supply.
The signal drives one transistor on while the other is off,
so in a Class B amp, no power is wasted going from the
positive supply straight to the negative supply.

Class AB amplifiers are almost the same as Class B amplifiers
in that they have two driven transistors. However, Class
AB amplifiers differ from Class B amplifiers in that they
have a small idle current flowing from positive supply to
negative supply even when there is no input signal. This idle
current slightly increases power consumption, but does not
increase it anywhere near as much as Class A. This idle current
also corrects almost all of the nonlinearity associated with
crossover distortion. These amplifiers are called Class AB
rather than Class A because with large signals, they behave like
Class B amplifiers, but with small signals, they behave like
Class A amplifiers. Most amplifiers on the market are Class AB.

Some good amplifiers today use variations on the above themes.
For example, some "Class A" amplifiers have both transistors
driven, yet also have both transistors always on. A specific
example of this kind of amplifier is the "Stasis" (TM) amplifier
topology promoted by Threshold, and used in a few different
high-end amplifiers. Stasis (TM) amplifiers are indeed
Class A, but are not the same as a classic Class A amplifier.




Keith

[greggz]

There is also a Class G starting to show up more and more as space gets tighter and tighter. The new Outlaw Audio slimline Monoblock amps are Class AB/Class G.

Class G amplifier - Class G operation involves changing the power supply voltage from a lower level to a higher level when larger output swings are required. There have been several ways to do this. The simplest involves a single class AB output stage that is connected to two power supply rails by a diode, or a transistor switch. The design is such that for most musical program material, the output stage is connected to the lower supply voltage, and automatically switches to the higher rails for large signal peaks. Another approach uses two class AB output stages, each connected to a different power supply voltage, with the magnitude of the input signal determining the signal path. Using two power supplies improves efficiency enough to allow significantly more power for a given size and weight. Class G is becoming common for pro audio designs.

Gregg

[Zzap]

Class D amps are only used for special applications like bass-guitar amps and subwoofer amps

Apparently there is a Danish company that has produced a class-D digital amplifier.

For the curious:

http://www.soundstage.com/revequip/robert01.htm

but don't get too excited - it costs $10k!

(Edit
Bang & Olufsen have a variation they call ICEpower:

http://www.icepower.bang-olufsen.com/sw1059.asp

These have shown up in various products

[doodleboytoy]

Sorry... kinda getting confused with all the classes :LOL:

Are you saying that a class AB will sound better than a class A for stereo/HT or is it just better value with marginal benefits? I am comparing the Rotel 1080 (200w) or 1090 (300w) with 1055 as receiver pre pro vs. Musical Fidelity A3.2 pre-amp plus two A3.2 amps (at 130w each - bi-amped).

Musical Fidelity's A3.2 is class A and from another forum they said that it would be better than the Rotel set-up.

:?:

[Danbry39]

Here's what I would say. Class A amps are the best overall sonic performers, but with the downside of the amps getting very hot and being energy hogs. A class A/B amp usually will sound just as good at low to moderate volumes due to the fact that it is running like a class A amp before the class B kicks in. For instance, my Parasound amp runs class A for the first 5-10 watts, which means that it will be running class A up to and above 90 decibels, afterwhich class B kicks in.

I should mention that I'm not the authority here and could well be off in what I'm saying, but this is my understanding (misunderstanding?) My impression is that Class A/B amplifiers try to take advantage of the positive aspects of both Class A and B amplifiers, which eliminating or reducing the negative aspects of these types of amps. The definition I cited above said:

Briefly, Class A amps sound the best, cost the most, and are the
least practical. They waste power and return very clean signals.
Class AB amps dominate the market and rival the best Class A
amps in sound quality. They use less power than Class A,
and can be cheaper, smaller, cooler, and lighter.

All that said, Musical Fidelity has an outstanding reputation and people here at HTGuide have spoken highly of Musical Fidelity components that they've owned.

Is it possible for you to audition both and also to compare the performance of each to your Rotel pre-pro? Again, I'd want to do so personally before buying as I'd want to make sure the improvement in two channel sound justified the expense. The performance of Rotel pre-pros in two channel is generally excellent as is.




Keith

[Danbry39]

Just found an explanation that simplifies the understanding of the categories. It states:

Think of three cars at a stop light. The class A car keeps the engine running at full power and full RPMs ready to take off at any time. The class B car shuts off the engine entirely and must re-start and get in gear before it can take off at the green light. The class AB car keeps the engine running at idle with the gear in drive using some power but not as much as the class A car and being much quicker off the line than the class B car. Class AB amplifiers are the most commonly used amplifier designs thanks to their attractive blend of reasonable efficiency and high-quality output (low distortion and high linearity close to but not equal to class A amplifiers).

Keith

[Scarp]

So, if its a B class amp, there would not be much idle power comsumption right? If its A it would be half of its power rating. If its AB it would be somewhat less than half.

Look at the idle comsumption figures then:
http://rotel.com/support/techups/techup-10-2.htm