Double down, good or bad?


I came across this article on Atma Sphere's website:

http://www.atma-sphere.com/papers/myth.html

In short, Atma Sphere believes having a power amp that is capable of doubling its power when impedance is half is not necessarily a good thing because speakers in general do not have a flat impedance across all freq range.

On paper, it does make sense. Though I am sure speaker designers take that into consideration and reduce/increase output where necessary to achieve the flatest freq response, that explains why most of the speakers measured by Stereophile or other magazines have near flat responses.

But what if designer use tube amps to design his speakers, mating them with solid state should yield higher bass output in general? Vice versa, tube amps yield less bass output at home?

I have always been a tube guy and learned to live with less bass weight/impact in exchange of better midrange/top end. Will one be better off buying the same exact amp the speakers were "voiced" with, not that it will guarantee good sound, at least not to everyone's ear.
semi

Showing 3 responses by audioquest4life

I am not a techie on the level of Nelson pass or Atmapshere (still learning), but I do have some experiences of my own, using a well built tube amp, one can use almost any speaker regardless of load, if the amps are built correctly. For example, many folks like to state that B&W or Magneplanar speakers are very hard to drive and require at least 200 watts or more. The tube amps I use drive these types of speakers easily and make wonderful music. I have been on the tube rolling circus and also discovered with the right combination, I can turn off my massive 15" subwoofer as these amps deliver deep enough to not have a sub. On some really stuff, such as deep pedal organ's, well I have to have the sub on, but the slam of the kick drum is all there.

From the reports that are starting to fill in on these amps, I think that those that state that tubes doen right are great with almost any speaker load. My amps are rated to handle loads as low as 2ohms.

http://www.octave.de/english/products/PowerAmplifiers/INFO-MRE130.htm

http://www.sixmoons.com/audioreviews/octave3/octave.html

Ciao,
Audioquest4life
This is a very enightening thread. I have followed along as I used to be real SS die hard, considering even to delve into ultra ML or Classe stuff until I heard a pair of excellant tube amps that were designed to operate on 4 ohms, and drive low impedence speakers:

Push-pull mono output stages with new driver electronics for the output tubes. This all-new design improves the transient response with complex loads and reduces distortion - particularly when low impedance speakers are connected. Ideal for critical loudspeakers such as Martin Logan, Avalon, Audio Physik, Caldera, Isophon Vertigo and Europa.

Clearly, I can agree with Atmasphere on how a design is capable of perforimng such tasks as driving low impedance speakers, it is most likely the topology in that implementation that needs to be considered. My amps, the Octave MRE 130 are rated at 130, tested and reviewed at 140, but 100 watts into 8 ohms.

All I can say is with technology like that, I can drive easily a pair of B&W 800's in my 25x18.5 listening room with thunderous bass and more than enough volume to make it concert level. The addition of the so called "Super Black Box" and their promised benefits in bass control and 2-ohm stability. The Super Black Box has an additional 100 plus amps of current and capacitance. I am not sure how other companies would implement such a feature, perhaps larger power supplies, but this concept works with these amps.

I believe that that tube amp builders who design amps capable of driving low impedance speakers from the start are actually doing the audio community justice.



Ciao,
Audioquest4life
Hi Atmasphere,

I do have some other thoughts from what you posted above about driving certain speakers with specific electronics, especially tubes. First off, I respect highly what you and others have to say in regards to the technical aspects of certain types of equipment. Granted, you design and sell tube amps; specifically of the Output Transformer Less variety (OTL). You even stated your self that certain electronics and speakers do not match well and the only way to know for sure is in real world listening tests. I am listening to some great music right now (vinyl of course) on my all tube setup and kicking the crap out of my B&W 800’s with live energetic and excellent sounds from a pair of little 140 watt mono amps and the bass, midrange and highs are all excellent. The 800‘s replaced the B&W 802’s I had before (gave them to the wife for HD TV). The reason I am letting you know this information is so that I can impart from you some real world conclusions about tube amps and speakers that contradict your statements, not that I disagree with in your electronics prowess; it is that I do not agree that phase angle distortion and wicked impedance curves are going to stop people from enjoying music with certain electronics, and these electronics you seemed to limit yourself to because you have not heard all of the combinations either.

From what I have read in this post alone, your amps cannot drive B&W 802 because your amps are designed for a certain paradigm that contradicts what B&W may be using for their design paradigms, so perhaps a mismatch there. While other manufacturers are designing tube amps that do work with low impedance speakers such as Martin Logans, Magnepan and B&W’s. Obviously these types of tube amps are designed with a certain paradigm to match the low impedance of these types of speakers.

Your statement as read below:

“The Power Paradigm amplifier is a 'power source', i.e. it will make constant power into any load. That is the voltage and current will both vary. I don't know of an amp that does this but that is the ideal, just as there are no true 'constant voltage' amplifiers out there either- that is the ideal. Does this clarify things?”

So based on your own admission that you do not know of any amps that do this, I think I am not off the mark by stating that perhaps there are some in production and being used now. I know this particular amplifier design is considered a “Power Paradigm” as it has an external 6x 3300 Microfarad capacitors (Elkos) power supply in addition to the regular on-board power supply. The amp is a class A/B with a pentode push pull design and very minimal negative feedback. It is somewhat of a hybrid amplifier as the owners manual states but the outboard power supply provides impulse power as you stated, perhaps in the 10ms realm that you mention and enough to give big speakers the additional current from the amps to drive them easily. Then I start to get confused when I look at your posts stating;

*tube amp with B&W 802 =>weak bass

“and other speakers (like the B&W 802) that are more effectively driven by transistors.”

“In all cases it is inappropriate power response. This is the major reason why you get mismatch between amps and speakers, although I would be remiss if I did not point out that distortion in both transistor and tube amplifiers also plays a significant role in what we hear as tonal aberration.”

Based on your statements and my real world experiences, I am not just an audio geek but an IT engineer by trade; I have to absolutely refute your statements and have conclusions quite the opposite from what you stated.

I am living with both tube amps and B&W 802’s and 800’s and know for a fact with the right combination of tubes, I have realized that my amps can drive these speakers both to extremely loud SPL‘s and with deep enough bass that in some music you would think a subwoofer is on. In fact I thought at first when I gave up transistors to go with tubes, the bass may have appeared weak, but when I did some tube rolling, I realized that the amps have the capability to drive these speakers with great dynamic swings and effortlessly. The bass I was hearing had a natural taught and dry feel. It was what they call in German “Knackig”.

From what I am gathering about the posts, it seems as if the discussion is getting wrapped up in distortion levels mixed with phase angles and impedance curves versus the reality of actually driving certain speakers with watts and discounting other factors. I have heard a true 1 watt at 1 meter test done with various speakers and amps in a test lab in Germany to compare 1 watts vs. loudness. With a distortion level of only .05 at a given phase angle, no one is going to hear it, even at 1% at 96DB with loud rock music, it is not much of an issue, with an all tube setup at that loud of a SPL, someone is more susceptible to hear tube rush instead of harmonic distortion and clipping. We are talking about some serious minor issues. When a gross mismatch occurs, then obviously it will become known, but I just happen to have experiences that are totally opposite of what you are stating and therefore I cannot accept that all of your explanations are conclusive to every tube amp and speaker combination that is possible. I do like your amp designs and logical feedback in these forums, however as a user of the referenced products above with different experiences, I feel the need to convey my thoughts on the subject.

When I look at the spec sheet of a particular type of amp, I do not see why anyone having this type of amplifier would have a hard time driving a pair of B&W802’s or 800’s for that matter as I do without any issues. These are the specs for you if you are interested, note that there is less power at 8 ohms versus 4 ohms.

Output 140 W into 4 ohms (100 W into 8 ohms) Frequency response 3 Hz - 100 kHz Input impedance 210 kOhm Signal-to-noise ratio > 103 dB Damping factor 12 - constant from 20 Hz - 15 kHz Minimum load impedance 2 ohms

Its circuit incorporates additional reservoir capacitors to increase the current delivery of the power supply, counteract fluctuations in the supply voltage and suppress low frequency mains supply 'noise'.

A description of the outboard capacitance increasing power supplies:
The external current increasing power supply, Super Black Box, always results in an improvement in sound quality. The sound becomes more relaxed without losing pace; the subtle timbres of individual instruments become more defined, and the soundstage extends further into the distance. The improved stabilization of the power supply increases the pulse output of the power amplifier, making loudspeaker efficiency less critical. The amplifier will also handle speakers with impedances as low as 2 ohms.

Again I appreciate all of your technical answers to some of the inquiries here. So in light of what all has been said, however can it also be true some of the mentioned parameters such as phase angle and impedance variations when minimal do not affect sound as much as people think, at least listening pleasure. I am not saying that a big phase angle shift would not, but how many people have actually heard what a big phase angle shift does to sound, outside of incorrect match of speakers and amps and discovering that it “sounds“ bad. Often people hear other things from what an electronic measurements report sheet states, in cables, tubes, amps and speakers.

A Short story:
At the end of the day, when I packed my amps up in a McIntosh audio shop and disconnected them from the B&W 802‘s after a shootout with the MC501’s and 1201’s, the Mac amps were not happy campers nor was the owner of the shop. The customers asked what tubes amps I was using and how I made the speakers sound so good compared to the transistors. Of course the dealer stated you will never hear what a system will sound like until you get it home, but if it sounds like crap in the store, who wants to even take it home for a demo. I am not bashing Mac stuff, it sounds different and for me would make a great home cinema system, but the fact is other people heard the B&W 802’s with tubes in a Mac shop compared to premium Mac gear and preferred the particular tube amps I brought up to do the test and demo comparisons. For me that whole experience only reaffirmed that each individual must hear for themselves what will work and what will not work. The 1 watt at 1 meter test works real well. It is an easy test. if there is a lot more room to increase volume, then you probably have a good match. You are either going to like what you hear or not and if the phase angle is not perfect, do not be fooled to think that an amp can’t handle the load, it just might fool you.

Ciao,
Audioquest4life