Onemug
I agree with you that in the end its the music not specifications or circuit toplogy that we listen to. And one must keep ones eye on the ball when reading and comparing specifications when trying to make a purcahse decision. But it does lead to some interesting conversations and I really enjoy the learning that goes along with it.
Chuck |
Unsound, just so you know, Class A has nothing to do with push-pull vs single-ended. Also, a Class A amplifier's peak power will always be the same as its continuous power, IOW the 'headroom' rating will be 0db. An amp that has more that 0db headroom is likely an AB amp.
Krell's sliding class A approach (a similar form of that being first used by Brooks in the 50s if I recall right), allows the amp to run cool at low power. On account of its power supply regulation it should exhibit 0db headroom.
Changing the load impedance changes everything! Contary to popular belief it is not always a good thing that the amplifier power changes as the load impedance changes. There are speakers that are of course designed for this, and there are other speakers to which this behaviour is unacceptable (i.e. electrostatics, horns and full-range high efficinecy drivers to name a few).
This ability of transistor amplifiers has to do with feedback just as much as the fact that they are solid state. The effects of Negative Feedback in an amplifier runs counter to the way our ears have evolved over millions of years. As a result it is one of those things that we should always question. Once you do so *honestly*, a lot of other things get questioned too, but ultimately the right answers also yield better sound. BTW these comments have nothing to do with transistor vs tubes! -although many will think that they do. The underpinning issue is more fundamental. |
Atmasphere, thank you. I was aware of the above. I think your point about amps increasing power not necessarily being a good thing is well taken. As you well know as an amp may increase its power out-put into lower impedances, it will also decrease its power out-put into higher impedances. As you pointed out with some speakers that vary a great deal in impedance load this will have a rather negative effect. On the other hand speakers with steady low impdeance loads will benefit from such an amp. Once again its about using the right tool for the job at hand. |
Atmasphere, thanks for your informative comments. But I'm not clear on why it is unacceptable for some speakers to have an amp that increases power into a lower impedance load. My Martin Logans are superb, but among their very few weaknesses is the fact that they roll off the topmost treble...and the impedance in the treble is 1 ohm or less. Surely an amp that can deliver more power into this tough load has the potential to provide better treble performance...? |
Calanctus, I use Martin Logan clsiiz and Krell 350mcx. What a coincidence to this thread topic. What speakers do you use? I was wondering the same thing as you after reading this thread! |
I hate answering my own questions but after several attempts to get Klipsch to answer with regards to my Palladium 1Ks running 125 watts in class A (and threatening to call Mondial directly). I finally got a response. A completely unqualified yes its absolutely the truth. I still find it kind of hard to believe given the amps' weight (each monobloc is about 70 lbs) and temperature, but that was a major company going on record by e-mail that it is true. No mention that you need to be playing them into 8 ohms but I'll save that for another day. Thanks for your patience and to you other secret Palladium owners out there in audioland now you know. |
Atmasphere,
Careful here. The ability of the ss amp to "double down" is
really a function of the regulation of the power supply in
conjuction with its power reservers. This is not really
negative feedback.
Additionally, it's the feedback on the gain stages for the
signal that can have a deleterious effect on the sound
quality.
One can design a zero-feedback gain stage that is fed by
a well-regulated power supply that has, in essence feedback.
However, the sound of such an amp won't be compromised.
The only drawback is that the amount of headroom in such
an amp is not dynamic. As you pointed out, it doesn't
increase in power for short transients.
However, I'd wouldn't count on the dynamic headroom in any
case - I'd size the amp so that the continuous power level
meets my needs.
Dr. Gregory Greenman
Physicist |
Calanctus, Your speakers are a good example of what I was talking about. ESLs in general, regardless of their particular impedance curve, want to see the same power for a given sound pressure regardless of what their impedance is at a particular frequency.
In effect, they are driven by power.
If an amplifier driving speakers like this puts out a different amount of power into different impedances, the effect is a shift in tonality. This is why transistor amplifiers (in general) tend to be very bright on ESLs, as their 'constant voltage' characteristic causes them to put out a lot of power into the low impedance of the ESL at high frequencies. Some speakers (for example B&Ws) are designed to expect a 'constant voltage' amplifier, and so will have flat response in the room. This is much trickier with ESLs!
In essense, there are two paradigms competing in high end audio today- the 'voltage paradigm' and the 'power paradigm'. No-one talks about this!- but we see it all around us:
The Voltage Paradigm is the reigning test and measurement paradigm. It is only concerned about voltage, and so when measuring an amp or speaker, voltage is the only thing considered. 'Constant voltage' output refers to an amplifier that puts out constant voltage regardless of load (contrary to morbious' comments, this does not require power supply regulation to accomplish this- merely enough feedback). Such an amplifier is regarded by these rules to be 'load impervious'.
The problem lies in the fact that negative feedback runs counter to how our ears detect volume (higher odd orders being the key- these are enhanced by negative feedback). Additionally there is the question of whether or not a speaker is driven by voltage or power, and of course the answer is power. So the 'power paradigm' says that the amplifier will have little or no feedback to reduce the odd ordered harmonic that the human ear dislikes, and that the amplifer will produce (or attempt to produce) constant power into all loads. This, BTW, is very nice for ESLs, horns and magnetic planars. Amps that fall into this category are SETs, some OTLs, transformer coupled push-pull tube amps and a very small number of transistor amps with zero feedback. Such amplifiers typically have higher output impedances, and nearly all will be unsuccesful at the goal of constant power (in fact many designers of such gear may not even acknowledge that they even *have* such a goal).
A parallel controversy is the subjectivist/objectivist debate. Roughly, the power paradigm is more subjectivist and vice-versa, but this is *not* by any means cast in concrete!
The power paradigm has its roots much further back than the voltage paradigm (1920s), and only seemed to resurface in the last decade or two. The obvious proliferation of advanced SETs (and tubes in general), horns, single driver full range speakers and the like are an indication that no-one has all the answers. |
Atmasphere, thank you for your explanation. Although I'm no EE I think I understand what you're getting at. I will have to try a suitably high quality and high power SS amp on my panels to see what it does to the treble.
Yada, currently I am using the Odysseys; their midrange is simply excellent, and they have good dynamics, but (as mentioned) they are not the equal of my previous ribbon speakers in the topmost treble. (Overall a much more musical experience; it's the midrange that counts the most!) |
If an amp is rated 200watts @ 8 oms and 400 watts @ 4 oms what is the 3oms rating.
The reason I ask is Im trying to match components with Thiel CS 2.4 speakers I just purchased.
Thanks,
Dave |
Charlot
To keep it simple - the benefit of the Class A amplifier is in it's sonic product! This is one of those things that is ineffable and must simply be heard and compared.
I have been listening to Class A amplification since the late 1990's and have no complaints. In 2005, I built a 1 watt SET that currently supplies my sonic entertainment.
Keep in mind that transistors as well as tubes can run in Class A. In fact, transistors in Class A come pretty close to doing tube-like stuff sonically.
Hope this helps.
Studio1 |
It depends on the amp. In theory if it is a solid state amp we would hope to see 600 Watts @ 3 Ohms if the amp is rated as 200 watts @ 8 Ohms. This generally doesn't apply to tube amps. Not all (in fact few) amps are capable of this kind of power delivery. Don't assume an amp is capable of this. |
Spear11,
It depends on the amplifier; the regulation of its voltage and its current output capacity.
We've been discussing amps that "double down" - those that will double their power
if the load impedance is halved. If we let V be the RMS voltage; then we can use
equations for power that look like the DC equations - but the use of the RMS values
make them applicable for AC power.
For a voltage source, the power P = V^2 / R; or P*R = V^2 = a constant if V is strictly
regulated. If the amp is rated at 200 watts at 8 ohms, then V^2 = 1600 volt^2. For
your 3 ohm speakers, P * (3 ohms) = 1600 volt^2.
Therefore, P = 533.3 watts.
Now this also presupposes that the amp has the current reserves to fulfill this. For
200 watts at 8 ohms; the current is given by P=(I^2)R; so that the current I = 5 amps.
For 533.3 watts at 3 ohms, the current will be 13.33 amps.
IF [ big IF ] the amp has the current reservers to output 13.3 amps, and the voltage is regulated to be the same irrespective of load impedance; then this hypothetical amp
can put 533.3 watts into the 3 ohm load.
Dr. Gregory Greenman
Physicist |
The Pass XA.5 series is single-ended, class A, and doubles down going from 8 ohms to 4 ohms. |
>> 01-19-06: Aball
>> No. The sonic benefit is that the entire signal is
>> swung by a transistor (or several in parallel) instead
>> of individual halves of the signal being split up by
>> two different transistors. Since there is no "handing
>> off" of the signal to another transistor, there is
>> potentially less distortion.
I hate to say this Aball - what you have explained above is single-ended operation & not class-A operation!
it just so happens that many/all single-ended tube & s.s. amps are class-A.
For class-A operation the transistor is biased along the load line in such a way that it always has max current flowing thru it whether a music signal is input into it or not. hence the heat dissipation.
s.s class-A amps can be single-ended (Aleph series) or can be push-pull (almost every other model).
In push-pull you will have P & N type transistors but it is not necessary. For example the Plinius SA-250 has N type push & N-type pull. Slightly higher output impedance i.e. lower damping factor but all N types can be matched better.
I'm sure that you know all of this as you are trained as a EE, I think? Probably wrote your post in a hurry or while cramming for an exam the next day?
FWIW. |
