[RDavidson]

The obvious answers which come first to mind are the XA.5 and XA.8 series amplifiers from Pass Labs, and Clayton amps.  MSB's big monoblocks appear to be fully class A.
One brand I have not seen mentioned in this thread is Vitus; they make some glorious sounding amplifiers, both pure class A models and higher power class AB models.
If one is really concerned with power consumption, my advice would be to either get some efficient speakers and go with something low power like a Pass XA 30.8, or, go to the other extreme, and end up with a well implemented Ncore class D amp.  With good system matching, a well massaged Ncore amp can sound very, very good.

Actually, at idle, 30 watt Class A amps like the 30.8, will consume 200 watts or more continuously from the wall. Not green by any stretch, but not bad either. To me, the sound is worth the power sacrifice. As has been said earlier, people use FAR more energy on other things daily without a second thought. I very much agree that there are some fantastic sounding Class D amps out there, if you're really concerned about energy consumption.

I know Class D amps are mostly known for their massive power while being very efficient. I'd personally like to see more development in the realm of lower power (no more than 50 wpc), simple circuit, Class D in an effort to get to the sound and low distortion specs of Class A. That'd be sweet, wouldn't it?

Given my room size and typical listening levels, I have found (exactly as Roger has been saying), that I absolutely don't need 100+ watts whatsoever. My speakers are average sensitivity, if not somewhat low sensitivity and I have yet to see the bias needle on my Pass 30.5 budge more than a hair, and that's at LOUD levels. Note I'm using a passive preamp too (zero gain buffered passive actually), as my source voltage (which Roger also mentioned) is enough to drive the amp to full output, easily.

With all this said, it'd behoove people to really take more things (ie room size, listening levels, speaker sensitivity, voltage gain) into consideration when buying gear to really map out their true needs in an effort to optimize system performance and synergy.

[FullRangeMan]

Now is too late to save energy, when Nikola Tesla purpose Free Energy and wireless transmission he was deleted.
This eco green stuff is a way to blame the people for the mistakes of past leaders.

I stick with Class A and tubes;

[RDavidson]

A note some may find interesting, the realization that I don't "need" a ton of power came when I was using my trusty old NAD 3020 to break-in a pair of vintage speakers I rebuilt. If you're familiar with the 3020, you'll recall the power meter on the front of the amp. I had to totally CRANK the volume to make the 35 wpc light even flicker on heavy bass. I didn't blow myself out of the room because I had the speakers facing each-other, out of phase.

After that, I started looking into the highest quality lower powered amps I could afford.....which naturally lead me to Class A solid state and lower powered tube amps.

[bardamu]

Hello,
It is obvious that you need a device that is well constructed. A beefy power supply and you need high efficiency speakers. In this link you can read about some test( that is if you can read French) The man who did write is rather famous in France.The test were done with hhigh effiency drivers but still he states that you will need an amp of about 30 to 50 watts capable of delivering enough headroom. Joni Mitchell and an acoustic guitar will do with a 300b single ended but if you listen to Duke Ellingtons big band you need more. Your device that runs out of power will function as a compressor. Happy reading, Edward
http://www.petoindominique.fr/php/puissance.php

[RDavidson]

Hello,
It is obvious that you need a device that is well constructed. A beefy power supply and you need high efficiency speakers. In this link you can read about some test( that is if you can read French) The man who did write is rather famous in France.The test were done with hhigh effiency drivers but still he states that you will need an amp of about 30 to 50 watts capable of delivering enough headroom. Joni Mitchell and an acoustic guitar will do with a 300b single ended but if you listen to Duke Ellingtons big band you need more. Your device that runs out of power will function as a compressor. Happy reading, Edward
http://www.petoindominique.fr/php/puissance.php

While I generally agree that higher sensitivity speakers are the way to go (and most speakers today are reasonably high sensitivity) there are some wonderful speaker designs out there that just don't come alive without more power than 30-50 watts without audible compression. Again, this all greatly depends on the size of one's listening room and average listening levels. This is just as important a factor as amp power and speaker sensitivity, and is sometimes forgotten. One could easily have what many would consider insensitive speakers by today's standards (maybe 85 db at 1 watt at 1 meter) and a somewhat low power amp (30-50 wpc), but have plenty of headroom if they sit rather close to the speakers (maybe no more than 2 - 2.5 meters away).

[jupiterboy]

Sudgen makes some Class A SS amps. Audio Note makes some single-ended Class A valves.

[Roger A. Modjeski]

Wasn't it Jim Salk that showed how transients were clipping a lower powered amp and when matched with a bigger amp, consumption soared to 300w during intense passages?

That and I hear a clear difference between using the 75w from my receiver and my 360w Rotel amps.  Even though my line arrays are around 99db/1w efficient.  Any explanation for this would be great.

This is interesting. I don't know Jim Salk. If you find the article I will be happy to read it and comment. In the larger amp the consumption from the wall could soar because it is a big amp and that is what big amps do. Unfortunately most of that power was turned into heat. Another possibility is the amp became unstable or the bias went way up briefly which I have seen in some big amps. In any event looking at the power consumption from the wall is not the way to look at this.

I do know my own system and I have an oscilloscope which is one way to see the peaks. The other is a peak and hold digital meter as I have suggested.

Unless you listen very loud the difference in the receiver and Rotel amp is likely in their circuitry not their power. Receivers tend to run low bias, have aggressive protection circuits and not the best designs. It is a matter of economy.
 
We need to know four things to answer your question sensibly. I am putting these in MY order of importance.

1. How loud do you listen peak and average? (mandatory to answer this post)
2. How far are you from your speakers. 
3. What is your speaker efficiency and type (point or line source)
4. Does you speaker have any severe peaks or dips in the impedance curve.
5. How large is your room. (optional)

[jtwrace]

1. How loud do you listen peak and average?
2. How far are you from your speakers
3. What is your speaker efficiency and type (point or line source)
4. Does you speaker have any severe peaks or dips in the impedance curve.

I'd also add


5. How large is your listening room?

[Roger A. Modjeski]

While I generally agree that higher sensitivity speakers are the way to go (and most speakers today are reasonably high sensitivity) there are some wonderful speaker designs out there that just don't come alive without more power than 30-50 watts without audible compression.

RD, I have experienced what I believe you are expressing, however, what is wonderful about a speaker that compresses at low levels? How loud is it going to get at 30-50 watts? What is going to happen to your ears? What is causing the speaker to do this?

I love Electrostats because they are lively at low levels and I can enjoy dynamic music without the fatigue of high levels. Perhaps you are saying what I believe to be true: Some speakers have to be played loud to hear all the music because at low levels they do not play the details of the music well. I call this property "sticktion". When one electron goes through a voice coil does it create enough force to get past the "stuckness" of the mechanics of a cone speaker? However if one electron goes on the stator of a Electrostat it indeed alters the force on the diaphragm and the diaphragm is much more free to move than the rubber surround and treated cloth of the surround.

Another analogy is static vs sliding friction. If you want to push anything there is a certain force it takes to get it started ( to overcome the static friction) once it is moving the sliding friction is less so less force is required. Perhaps this applies to cone speakers, more to some than others.

[Roger A. Modjeski]

I'd also add


5. How large is your listening room?

We can and I will though I find it is not a big effect unless there are lots of reflections which a good room should not have. Unless you are very far from the speakers it won't make much difference for this determination. What really gets me is hardly anyone mentions their SPL, so that gets us nowhere.  In my study of this subject I have found that there is a much greater difference in people's listening level than there is typical speakers. For some numbers: Average speakers vary from low 80's to low 100's thats 20 dB. My survey of listeners gave reports from 70 db to 110 dB SPL. that is 40 dB. This is why I ask everyone what their listening level is.  If I turn it up really loud I get 95 dB peaks and I can't imagine listening any louder. Most of my listening is at 60 dB average, 75 peak.

I am waiting to hear some voltage measurements.  Saturday is a great day for experiments, get those meters out. Any kind will do.

[jtwrace]

You might find this thread interesting. 

[RDavidson]

RD, I have experienced what I believe you are expressing, however, what is wonderful about a speaker that compresses at low levels? How loud is it going to get at 30-50 watts? What is going to happen to your ears? What is causing the speaker to do this?

I love Electrostats because they are lively at low levels and I can enjoy dynamic music without the fatigue of high levels. Perhaps you are saying what I believe to be true: Some speakers have to be played loud to hear all the music because at low levels they do not play the details of the music well. I call this property "sticktion". When one electron goes through a voice coil does it create enough force to get past the "stuckness" of the mechanics of a cone speaker? However if one electron goes on the stator of a Electrostat it indeed alters the force on the diaphragm and the diaphragm is much more free to move than the rubber surround and treated cloth of the surround.

Another analogy is static vs sliding friction. If you want to push anything there is a certain force it takes to get it started ( to overcome the static friction) once it is moving the sliding friction is less so less force is required. Perhaps this applies to cone speakers, more to some than others.

Yes. This is EXACTLY what I'm talking about. And, yes, my experience with this applies to cone speakers. That's not to say that some of these mechanically "stuck" speakers don't sound good or aren't enjoyable, it's just that they have to be fed more power (ie played louder to breathe). I'm not a fan of this. Like you, I'd much rather listen / hear all the music at reasonable (relaxing / ear preserving) levels.

[Roger A. Modjeski]

You might find this thread interesting.

Thank you for that link. Readers should see that the majority of poll responses is below 2 volts. THe only thing I dont like about this test is it doesnt use music. How do we compare a single frequency to music?

Come-on guys,  Get out those meters and measure your MUSIC, Hey Music is our reference here at Music Reference

[jtwrace]

Thank you for that link. Readers should see that the majority of poll responses is below 2 volts. THe only thing I dont like about this test is it doesnt use music. How do we compare a single frequency to music?

Come-on guys,  Get out those meters and measure your MUSIC, Hey Music is our reference here at Music Reference

There is another thread that he did where you would use music and then measure it (which I did).  The problem was that the music was very dependent on the results.  This is just a more controlled way.  However, you can do both!   

[bardamu]

Hello,
Just take a closer look at the link thjat i did post and you will see that this electric engineer did use music to explain his theory. A pity for you it is in French. You can try to read between the lines and look at the scope pics. Greetings, Edward

[Roger A. Modjeski]

Hello,
Just take a closer look at the link thjat i did post and you will see that this electric engineer did use music to explain his theory. A pity for you it is in French. You can try to read between the lines and look at the scope pics. Greetings, Edward

I did take a closer look and translated the page. I put in my statistics

peak listening level 95 db
2 speakers
distance at listening 3 meters
speaker 93 db/watt

the result was 3.2 watts.

[Carl V]

1. How loud do you listen peak and average? (mandatory to answer this post)
65-85 most of the time.  Occasionally 95+

2. How far are you from your speakers.
9 feet nearly equilateral triangle

3. What is your speaker efficiency and type (point or line source)
85.5 & Point source. (MTM)

4. Does you speaker have any severe peaks or dips in the impedance curve.
4ohm. 58ohm at20Hz saddle at 50Hz next valley peak is 36ohm at 80Hz then the next at 1800
no idea about phase angles. 85.5 @ 2.83

5. How large is your room. (optional)
1st 13x21x8
2nd 22'x32'x8'


I will locate my Volt meter and run some numbers.
around 2.1 volts @ 85~ish dB
2.7 volts is a peak at 95dB
** ??
I have had had  Snell active X-overs, marchand Bassis
and Feedback destroyers, Ranes etc., handing off to two Tumults.
Abd have also utilzed Powered bass cabinets...e.g., two Aurasound
10" drivers with Hypex plate amps with a passive High Pass for the MTM.



(another MTM is 93.5 4 ohm & more benign)

[RDavidson]

Hello,
Just take a closer look at the link thjat i did post and you will see that this electric engineer did use music to explain his theory. A pity for you it is in French. You can try to read between the lines and look at the scope pics. Greetings, Edward

Actually, Google can translate the link to English (and other languages).
I tried using the calculator, but don't understand what is meant by "critical distance." I admit that I haven't carefully read everything. A number has to be typed in the blank for critical distance or the calculator won't provide a result. Is the critical distance, essentially the maximum listening distance to consider? Layman's terms, please. It's Saturday. 

[bardamu]

Hello,
If i am right if you are sitting to far away from the loudspeakers most of the sounds are reflected sounds having the same spl. If you move closer you will hear reflected plus the sound coming directly from the speakers.
The next under the calculations is important. They did connect a scoop with a good memory function and that did show that especially in the lower frequency range the power needed is much larger than expected. The man who did wrote this article did work in the professional field of installing/designing sound and image for movie theatres. I was this attend a meeting with a diy group in Paris in a movie theatre with a real good dolby surround system.
Sincere greetings, Edward

[Roger A. Modjeski]

Actually, Google can translate the link to English (and other languages).
I tried using the calculator, but don't understand what is meant by "critical distance." I admit that I haven't carefully read everything. A number has to be typed in the blank for critical distance or the calculator won't provide a result. Is the critical distance, essentially the maximum listening distance to consider? Layman's terms, please. It's Saturday. 

I used the Google translator to get an understanding of the calculator and run my numbers. I studied the graph and saw that the "critical distance" is where the SPL tends to level off after dropping 6dB/double the distance as point sources do. I used 2 meters as the critical distance for my first run. For my second run I use 3 meters, the same as my listening distance. The fun thing about calculators like that is to play with them and see what happens. That time the power came out at 7 watts. Still a low number.

As this discussion progresses I see that we are still in the low numbers for power. This post already has me thinking of how to make a good 10-20 watt Class A SS or possibly hybrid amp with a very simple circuit. What I am thinking about is single tube driving a pair of MOSFETS. I have made some of these before but had not considered making one class A at low power. At the time I was still in the 100+ watt camp with the rest of you. I'm not in that camp so much anymore.

The buying public should realize that they have a powerful effect on what we as designers do. When asked "why do you make a 100 watt/ch amplifier I say: I don't think anyone needs one but they think they do. A low power amp is hard to sell." Fortunately low power is getting some attention. There is a low power circle here. http://www.audiocircle.com/index.php?board=195.0

I don't agree with everything the low power people believe. I do not think single ended amps with high 2nd harmonic distortion are a good thing. No type of distortion is benign. However I appreciate that they do understand that with modern more efficient speakers less power is needed. I also appreciate that they have learned that a lot of reserve power is meaningless. That is the reason I got involved in this discussion.

I will say it again. A 100 watt amplifier with 99 watts of unused power does not control a speaker or make any difference. What controls a speaker is high damping and available current. What we need is an amplifier that sounds the same right up to clipping. The whole concept of headroom needs to be looked at. Shall we start a post on that?