[yuri777]

I have a question for Hugh.
Will the AKSA 100 require any modifications to drive 4 Ohm speakers such as Magnapans 2.7s?

Thanks

[AKSA]

Hi Yuri,

Thank you for your question.

Maggies are no problem at all, in fact the 55W will handle them extremely well, as I discovered when I first listened to AndyR's Maggies about 18 months ago.

The 100W will go down to a 2.5R load without encroaching on SOAR issues.  It is reliable at this impedance, too.

Cheers,

Hugh

[pauly]

On the subject of what the AKSA 100n will drive , Hugh, how would it do with line source speakers like the gr research Alpha LS?





Paul

[andyr]

I have a question for Hugh.
Will the AKSA 100 require any modifications to drive 4 Ohm speakers such as Magnepan 2.7s?

Thanks

Hi, Yuri777, I am driving my Maggie IIIas in an active setup - so each AKSA module just sees the load of one driver.  I don't know what each driver on the 2.7s are but the IIIa ribbon is 3ohms, the mid panel is 3ohms and the base panel is 4ohms.

Absolutely no problem for the AKSAs!!

Regards,

Andy

[AKSA]

Pauly,

I really need to know how many drivers, impedance, and how they are configured.  Failing that, could you give me the URL and I'll have a gander and get back to you.

I have a pet peeve with loudspeakers of impedance less than 2R, I doubt these are that low;  usually four speakers or more are wired in series/parallel so that impedance is not too low.

Cheers,

Hugh

[jonwb]

Pauly,

I really need to know how many drivers, impedance, and how they are configured.  Failing that, could you give me the URL and I'll have a gander and get back to you.

I have a pet peeve with loudspeakers of impedance less than 2R, I doubt these are that low;  usually four speakers or more are wired in series/parallel so that impedance is not too low.

Cheers,

Hugh

I don't think there would be a problem from an impedance standpoint (they run about 8ohms).  I wonder about what might make one amp better than another at driver control (damping factor?) and if this many drivers might make it more difficult to manage?

Anyway, here's the link:
http://www.gr-research.com/AlphaLS/Alpha.htm

I currently have a set that is under construction and plan on initially driving them with a set of IRD MB-100's that I purchased from fellow forum member Nathanm.  I’m curious to see how these little amps manage those beasts.  

Its funny when you see all those drivers its counter-intuitive to think that all those drivers technically make you need less power not more (higher efficiency, especially with the vented enclosure).

Jon

[pauly]

thanks Jon,
Any advice Hugh re: damping factor etc.
 



Thanks           Paul

[AKSA]

If the GRs are around 8R, there can never be any problems with an AKSA driving them, even at high levels.

Let me give my thoughts on damping factor.    

When negative feedback was all the rage in the seventies, and amps produced very low advertized distortion at rated power into 8R resistive loads, feverish marketing departments discovered an impressive, marketable figure;  damping factor (DF).  They could measure the output impedance of the amp at a favourable frequency, usually 1KHz, and then divide it into the 8R load impedance and derive a most alluring quotient, often around 100 or more.  The truly 'impressive' designs pulled up to 400!!  My!!  This was almost as good as drag racing!!  

The assumption was that the amplifier could very easily control the exact position of the cone with DF this high.  Of course the truth is rather less impressive, since other factors intervene.  Dang, life is never simple...

A loudspeaker has, amongst other parts, a voice coil attached to a cone and a powerful magnet with thousands of intersecting lines of force through that voice coil.  When a current (notice the use of the word current, NOT voltage) passes through the VC, the flux lines react and push the cone forward or back.  However, as the voice coil is now moving through a magnetic field, a back emf is created across the voice coil which 'fights' the voltage applied by the amplifier to the voice coil.  It is the difference between these two voltages which is fed back to the amplifier as voltage feedback.  Of course, this voltage must also pass backwards through the crossover, but that's another story!!  This has spawned an argument about current feedback, which rages even today...  Now, this current is phase shifted over the initial input since it is a reaction after the [mechanical] event AND it must pass through the crossover, and this is the reactive kickback so touted which can destabilize amplifiers, particularly those using global negative feedback.  It's what makes a speaker 'hard to drive'.

It also turns out that a tube amplifier, with a damping factor of perhaps ten, sounds great, and in fact there are significant qualities to tube amp bass which SS amps don't have!  You've only to listen to a SET with a damping factor of 5 to scratch your beard in disbelief!     I recently listened to an 845 PP Class A amp of 35W, pulling a B+ of 1200V, and the bass of this amplifier, with a DF of about 10, was absolutely huge, just incredible.  (I confine my comments to bass here, say below 100Hz).  And it was intensely musical, too, so there's more to this ditty than meets the eye.....

Something amusing I read recently:

'The Titanic was built by professionals, the Ark by amateurs'.  

These desirable acoustic qualities of tube amps have to do with high levels of second harmonic at low frequencies.  They also relate to slightly loose control over the cone which promotes long decay (sometimes called reverberation, but that's generally added, whereas decay is natural), a quality, particularly in bass (and in human voice, but that's another story), which we humans very much like......

So, we expose yet another engineering compromise;  more DF means less decay, usually less H2, and a tight, controlled bass which however lacks the 'wetness' and 'humanity' we love in a tube amp.  What to do?

Well, we certainly need to have tight control over the cone, but not so much that there is no decay to bass notes, and after they are played, they don't die off immediately, leaving an acoustic void which is somehow unsatisfying.  Bear in mind that just about all drivers are actually designed for voltage feedback, since this suits more amplifier designs around the world, and we are stuck with this.  Interestingly, there are some instruments, notably the Bazouki from Greece, for which current feedback is more suited, but recording studios and speaker designers have been fixated upon voltage feedback for decades so that's what we work with.

It turns out that the AKSA solves this problem through its topology.  A bootstrap tends to 'wetten up' at low frequencies, at the cost of a little cone control.  But we need to give it good control, so that we have, for want of a better, less dissonant phrase, 'fast bass'.  (God help me for saying that....... )  This issue is also addressed in the AKSA, through the feedback network.

So, a high damping factor should be viewed with some suspicion, a low DF is certainly too woolly, around 60-100 is probably about right for a SS PP amplifier, but other steps should be taken to confer the qualities preferred by the organic lifeforms who listen to the system.  I venture to suggest an AKSA would sound terrible to a Venusian, but humans seem to like it.

Psychoacoustics is fundamental to a good high fidelity sound system, just as human anatomy is important to a clothes designer......

DF is not all it's cracked up to be - You can't describe a person's qualities by measuring his or her IQ - there's always more to it than that!

I trust this does not entirely confuse......   Ben and I are off to a working breakfast in an hour, and we will doubtless discuss this at length!

Cheers,

Hugh

[DVV]

Pauly,

I really need to know how many drivers, impedance, and how they are configured.  Failing that, could you give me the URL and I'll have a gander and get back to you.

I have a pet peeve with loudspeakers of impedance less than 2R, I doubt these are that low;  usually four speakers or more are wired in series/parallel so that impedance is not too low.

Cheers,

Hugh

Major, how does your stew cook with an impedance of 3R, but also with a phase shift of
-60 degrees? The amp effectively sees 1.5R.

Actually Hugh, I have seen this a few days ago, on one of Heco's newest speakers. It sounds very, VERY good, but is one nasty load to drive. On the other hand, it does 92 dB SPL 1W/1m, so you don't really need all that much power for normal listening, including fast and nasty transients.

The problem is usually not with stability or overheating (unless one is really overdoing it, but you can fry any amp that way), the problem lies with tonality shifts. This is a fancy way of saying that different amps will change in different ways when pressed harder into such complex and reactive loads. One amp will lose some of its clarity, for example, but will preserve its dynamics, while another might go flat on you altogether. Or anything in between.

This is why Hugh is so cautious about commenting some of the questions here, I think; he is aware there is no way under the sun any designer can anticipate every and all possible combinations, the number of which is the last thing before infinite.

But don't let me interrupt your pleasure, gentlemen, I daresay this is one of the more interesting threads on this site, and certainly a change from "wow, X has a new wahtever out, cheap, just $2K", etc.

Hugh, I don't know how you do it, but every time I drop in on your section, I find people asking really meaningful and thought out questions well worth answering. One of these days, I might move in here permanently.

Run my own school on all about amps.

Cheers,
DVV

[AKSA]

Dejan,

I was beginning to wonder where you were!  I'm glad you are back....

One point, I may be wrong, but impedance takes account of phase angle;  it's all a part of the reactance calculation, isn't it?

The good questions in this forum are entirely to the credit of the AKSAphiles here;  they seem to be much, much smarter than in other forums I've seen.  Ben and I try to keep the physics and psychoacoustics connected in our explanations, and we are bloody lucky to have such a crowd buying Aspen products!

Thanks, guys, for all the nice comments in the Support thread.  Saya sangat terharu.....  (I'm most touched)

Cheers,

Hugh

[DVV]

Dejan,

I was beginning to wonder where you were!  I'm glad you are back....

I never left. Just been busy lately, less time left to drop around.

One point, I may be wrong, but impedance takes account of phase angle;  it's all a part of the reactance calculation, isn't it?  [\quote]

In general terms, yes, it is. However, in practice, I find far too many people discussing the plain impedance without any side effects, and you can't disregard them because they are always there. The question is only by how much and in what way.

Hugh, we worked out behinds off while developing my 1041 monitors on precisely this aspect. To cut a long story short, eventually (as in 6 months and say 10-11 crossovers later) we managed to get it all down to a minimum impedance of 6 ohms with a worst case phase angle of -25 degrees. To the amp, this is about 5 ohms worst case all told, and that in a small section only (app. 80....150 Hz), after which it all stays just above 8 ohms, fairly constant.

The gruelling test was using the same amp to drive these, and then switching over to AR94s (volume adjusted for same loudness); most different behavior of the amp. A VERY interesting test.

The good questions in this forum are entirely to the credit of the AKSAphiles here;  they seem to be much, much smarter than in other forums I've seen.  Ben and I try to keep the physics and psychoacoustics connected in our explanations, and we are bloody lucky to have such a crowd buying Aspen pro ...

So I've noticed. What you do not mention, and what I like about it, is that along the way, you do manage to pass on an awful lot of level headed info, just what younger users need because, most unfortunately, they don't have much opportunity to read it straight, no dressing.

As I said, compare the questions here with the general circles and you'll see the difference; this is to the point, sane questions of relevance asked, over there it's mostly acquisition time, what do I buy.

Anyway, I don't want to party crash, just couldn't resist expressing my satisfaction, that's all.

Cheers,
DVV

[andyr]

Hi, Dejan,

Pleeze tell us more about these 1041 monitors of yours.

Regards,

Andy

[JohnR]

NOoooooooo.........

J/K DVV

[DVV]

Hi, Dejan,

Pleeze tell us more about these 1041 monitors of yours.

Regards,

Andy

Notwithstanding the omnipresent JohnR, a.k.a. The Ghost Who Walks, this is my very personal ego trip I saved from myself.

The hero is not he who saves the people from the villains, but he who saves the people from himself. Remember that, JohnR!

Profound thoughts done and written, my beef with the current industry is that it favors detail over the whole. My feeling is that speakers made 10-15 years ago were far better at reproducing the grand scale of things at the cost of some detail, whereas the current crop does detail better, but generally is very poor on the big picture.

The logical thought was - why do we not have both in a reasonably priced speaker? The answer was because there is none to find that I could dig up. The consequence was my pet project.

First I did some ugly people manipulation, and who else to, but a good and dear friend of mine, who just happened to be the chief engineer of a company now quite dead called B&M Acoustics. He was the M in the moniker. I challenged him to outdo himself and everybody else for about 1/2 the price of his best models at the time (which was a year and a half ago). One thing led to another, and he was game. Hard work, pushing a frog into water.

So I sat down and thought out the whole project. After some deliberation, I produced a design brief, outlining what was wanted, what was to be used to get it, and I added some pepper and spice, things I always wanted in speakers but could never get. Out of my own reverence for JBL's one and only 4312 monitor, I christened this one 1041 - 10" bass, 4" mid, 1" high.

That's the intro, for the rest of the story, plus the pics, read the review (not by me, of course, obvious conflict of interest) on my site, which is at http://www.zero-distortion.com .

The aftermath is that I have carted them to quite a few places and did A/B comparisons with quite a few speakers. Overall, they still lead the way by a nice margin.

Originally, they cost 1.200 euros per pair, FOB Belgrade. Not an insignificant price, to be sure, and remember that by the time it gets to you its price will be more like 1,800-2,000 euros. BUT, I challenge one and all to find a truly better speaker for the money, where "better" means at least three things another speaker does better.

Aha, you say, how can we buy a speaker from a defunct company? Well, the last I heard Mr M (which stands for Mirko) is seriously thinking about getting back into the business on his own, so it may just be that this model will be available once again.

Let me finish up by saying that other people generally concur with my views. For example, a friend from Belgium bought one, and another friend from Italy, and both are very happy with them. The Belgian actually had several of his friends wanting to order them, but the company broke up and this never came to pass.

If you want to discuss them further, concept and/or execution, fair enough, but let's think of another place to do so rather than misuse Hugh's hospitality here. If anyone opens a topic in say two channel audio, I'll participate.

Cheers,
DVV

[DVV]

I almost forgot (but not quite) ...

Hugh's diatribe about the damping factor is just as he said it. I'd just like to sort it out in a nice, neat list of factors which contribute to the damping factor:

1. Power supply (its output impedance, related to quality);
2. Output stage of the amp;
3. Drive of the output devices (predriver/driver is better);
4. Presence or absence of the output inductor (high range), and
5. Negative feedback (quantity AND quality).

As a general rule, any damping factor over 10:1 is deemed sufficient, but I admit to changing this to 20:1 on basis of what I hear in both cases. So, working backwards, if your worst case is 20:1 into 2 ohms, then it's 20/40/80:1 into 2/4/8 ohms.

Also, remember that it's almost never linear, always being higher in the lower registers (where it's required most) and lower in the higher registers. The difference could be anything, from say 2:1 low:high, to as much as 1:0,01 low:high. There are many reasons why this is so, so let's not try to bash them into a convenient quick form definition.

Cheers,
DVV